ALBERT

Description: The diagnosis of the conservation state of monumental structures from constraints to the spatial distribution of their physical properties on shallow and inner materials represents one of the key objectives in the application of non-invasive techniques. In situ, CRP and 3D ultrasonic tomography can provide an effective coverage of stone materials in space and time. The intrinsic characteristics of the materials that make up a monumental structure and affect the two properties (i.e., reflectivity, longitudinal velocity) through the above methods substantially differ. Consequently, the content of their information is mainly complementary rather than redundant. In this study we present the integrated application of different non-destructive techniques i.e., Close Range Photogrammetry (CRP), and low frequency (24 KHz) ultrasonic tomography complemented by petrographycal analysis based essentially on Optical Microscopy (OM). This integrated methodology has been applied to a Carrara marble column of the Basilica of San Saturnino, in Byzantine-Proto-Romanesque style, which is part of the Paleo Christian complex of the V-VI century. This complex also includes the adjacent Christian necropolis in the square of San Cosimo in the city of Cagliari, Sardinia, Italy. The column under study is made of bare material dating back probably to the first century A.D., it was subjected to various traumas due to disassembly and transport to the site, including damage caused by the close blast of a WWII fragmentation bomb. High resolution 3D modelling of the studied artifact was computed starting from the integration of proximal sensing techniques such as CRP based on Structure from Motion (SfM), with which information about the geometrical anomalies and reflectivity of the investigated marble column surface was obtained. On the other hand, the inner parts of the studied body were successfully inspected in a non-invasive way by computing the velocity pattern of the ultrasonic signal through the investigated materials using 3D ultrasonic tomography. This technique gives information on the elastic properties of the material related with mechanical properties and a number of factors, such as presence of fractures, voids, and flaws. Extracting information on such factors from the elastic wave velocity using 3D tomography provides a non-invasive approach to analyse the property changes of the inner material of the ancient column. The integrated application of in situ CRP and ultrasonic techniques provides a full 3D high resolution model of the investigated artifact. This model enhanced by the knowledge of the petrographic characteristics of the materials, improves the diagnostic process and affords reliable information on the state of conservation of the materials used in the construction processes of the studied monumental structure. The integrated use of the non-destructive techniques described above also provides suitable data for a possible restoration and future preservation.

Description: Copernicus

Description: Published

Description: On line

Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: Originating from the boreal forest and often transported over large distances, driftwood characterises many Arctic coastlines. Here we present a combined assessment of radiocarbon (14C) and dendrochronological (ring width) age estimates of driftwood samples to constrain the progradation of two Holocene beach-ridge systems near the Lena Delta in the Siberian Arctic (Laptev Sea). Our data show that the 14C ages obtained on syndepositional driftwood from beach deposits yield surprisingly coherent chronologies for the coastal evolution of the field sites. The dendrochronological analysis of wood from modern driftlines revealed the origin and recent delivery of the wood from the Lena River catchments. This finding suggests that the duration transport lies within the uncertainty of state-of-the-art 14C dating and thus substantiates the validity of age indication obtained from driftwood. This observation will help to better understand changes in similar coastal environments, and to improve our knowledge about the response of coastal systems to past climate and sea-level changes.

Description: Earth system and climate modelling involves the simulation of processes on a wide range of scales and within and across various compartments of the Earth system. In practice, component models are often developed independently by different research groups, adapted by others to their special interests and then combined using a dedicated coupling software. This procedure not only leads to a strongly growing number of available versions of model components and coupled setups but also to model- and high-performance computing (HPC)-system-dependent ways of obtaining, configuring, building and operating them. Therefore, implementing these Earth system models (ESMs) can be challenging and extremely time consuming, especially for less experienced modellers or scientists aiming to use different ESMs as in the case of intercomparison projects. To assist researchers and modellers by reducing avoidable complexity, we developed the ESM-Tools software, which provides a standard way for downloading, configuring, compiling, running and monitoring different models on a variety of HPC systems. It should be noted that ESM-Tools is not a coupling software itself but a workflow and infrastructure management tool to provide access to increase usability of already existing components and coupled setups. As coupled ESMs are technically the more challenging tasks, we will focus on coupled setups, always implying that stand-alone models can benefit in the same way. With ESM-Tools, the user is only required to provide a short script consisting of only the experiment-specific definitions, while the software executes all the phases of a simulation in the correct order. The software, which is well documented and easy to install and use, currently supports four ocean models, three atmosphere models, two biogeochemistry models, an ice sheet model, an isostatic adjustment model, a hydrology model and a land-surface model. Compared to previous versions, ESM-Tools has lately been entirely recoded in a high-level programming language (Python) and provides researchers with an even more user-friendly interface for Earth system modelling. ESM-Tools was developed within the framework of the Advanced Earth System Model Capacity project, supported by the Helmholtz Association.

Description: Numerous studies have addressed the possible existence of large floating ice sheets in the glacial Arctic Ocean from theoretical, modelling, or seafloor morphology perspectives. Here, we add evidence from the sediment record that support the existence of such freshwater ice caps in certain intervals, and we discuss their implications for possible non-linear and rapid behaviour of such a system in the high latitudes. We present sedimentary activities of 230Th together with 234U/238U ratios, the concentrations of manganese, sulphur and calcium in the context of lithological information and records of microfossils and their isotope composition. New analyses (PS51/038, PS72/396) and a re-analysis of existing marine sediment records (PS1533, PS1235, PS2185, PS2200, amongst others) in view of the naturally occurring radionuclide 230Thex and, where available, 10Be from the Arctic Ocean and the Nordic Seas reveal the widespread occurrence of intervals with a specific geochemical signature. The pattern of these parameters in a pan-Arctic view can best be explained when assuming the repeated presence of freshwater in frozen and liquid form across large parts of the Arctic Ocean and the Nordic Seas. Based on the sedimentary evidence and known environmental constraints at the time, we develop a glacial scenario that explains how these ice sheets, together with eustatic sea-level changes, may have affected the past oceanography of the Arctic Ocean in a fundamental way that must have led to a drastic and non-linear response to external forcing. This concept offers a possibility to explain and to some extent reconcile contrasting age models for the Late Pleistocene in the Arctic Ocean. Our view, if adopted, offers a coherent dating approach across the Arctic Ocean and the Nordic Seas, linked to events outside the Arctic.

Description: The modeling of paleoclimate, using physically based tools, is increasingly seen as a strong out-of-sample test of the models that are used for the projection of future climate changes. New to the Coupled Model Intercomparison Project (CMIP6) is the Tier 1 Last Interglacial experiment for 127 000 years ago (lig127k), designed to address the climate responses to stronger orbital forcing than the midHolocene experiment, using the same state-of-the-art models as for the future and following a common experimental protocol. Here we present a first analysis of a multi-model ensemble of 17 climate models, all of which have completed the CMIP6 DECK (Diagnostic, Evaluation and Characterization of Klima) experiments. The equilibrium climate sensitivity (ECS) of these models varies from 1.8 to 5.6 ∘C. The seasonal character of the insolation anomalies results in strong summer warming over the Northern Hemisphere continents in the lig127k ensemble as compared to the CMIP6 piControl and much-reduced minimum sea ice in the Arctic. The multi-model results indicate enhanced summer monsoonal precipitation in the Northern Hemisphere and reductions in the Southern Hemisphere. These responses are greater in the lig127k than the CMIP6 midHolocene simulations as expected from the larger insolation anomalies at 127 than 6 ka. New synthesis for surface temperature and precipitation, targeted for 127 ka, have been developed for comparison to the multi-model ensemble. The lig127k model ensemble and data reconstructions are in good agreement for summer temperature anomalies over Canada, Scandinavia, and the North Atlantic and for precipitation over the Northern Hemisphere continents. The model–data comparisons and mismatches point to further study of the sensitivity of the simulations to uncertainties in the boundary conditions and of the uncertainties and sparse coverage in current proxy reconstructions. The CMIP6–Paleoclimate Modeling Intercomparison Project (PMIP4) lig127k simulations, in combination with the proxy record, improve our confidence in future projections of monsoons, surface temperature, and Arctic sea ice, thus providing a key target for model evaluation and optimization.

Description: Methane plays an important role in the Earth’s atmospheric chemistry and radiative balance being the second most important greenhouse gas after carbon dioxide. Methane is released to the atmosphere by a wide number of sources, both natural and anthropogenic, with the latter being twice as large as the former (IPCC, 2007). It has recently been established that significant amounts of geological methane, produced within the Earth’s crust, are currently released naturally into the atmosphere (Etiope, 2004). Active or recent volcanic/geothermal areas represent one of these sources of geological methane. But due to the fact that methane flux measurements are laboratory intensive, very few data have been collected until now and the contribution of this source has been generally indirectly estimated (Etiope et al., 2007). The Greek territory is geodynamically very active and has many volcanic and geothermal areas. Here we report on methane flux measurements made at two volcanic/geothermal systems along the South Aegean volcanic arc: Sousaki and Nisyros. The former is an extinct volcanic area of Plio-Pleistocene age hosting nowadays a low enthalpy geothermal field. The latter is a currently quiescent active volcanic system with strong fumarolic activity due to the presence of a high enthalpy geothermal system. Both systems have gas manifestations that emit significant amounts of hydrothermal methane and display important diffuse carbon dioxide emissions from the soils. New data on methane isotopic composition and higher hydrocarbon contents point to an abiogenic origin of the hydrothermal methane in the studied systems. Measured methane flux values range from –48 to 29,000 (38 sites) and from –20 to 1100 mg/mˆ2/d (35 sites) at Sousaki and Nisyros respectively. At Sousaki measurement sites covered almost all the degassing area and the diffuse methane output can be estimated in about 20 t/a from a surface of about 10,000 mˆ2. At Nisyros measurements covered the Stephanos and Kaminakia areas, which represent only a part of the entire degassing area. The two areas show very different methane degassing pattern with latter showing much higher flux values. Methane output can be estimated in about 0.25 t/a from an area of about 30,000 mˆ2 at Stephanos and about 1 t/a from an area of about 20,000 mˆ2 at Kaminakia. The total output from the entire geothermal system of Nisyros probably should not exceed 2 t/a.

Description: Published

Description: Vienna, Austria

Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Description: open

Description: A biomonitoring survey, above tree line level, using two endemic species (Senecio aethnensis and Rumex aethnensis) was performed on Mt. Etna, in order to evaluate the dispersion and the impact of volcanic atmospheric emissions. Samples of leaves were collected in summer 2008 from 30 sites in the upper part of the volcano (1500- 3000 m a.s.l). Acid digestion of samples was carried out with a microwave oven, and 44 elements were analyzed by using plasma spectrometry (ICP-MS and ICP-OES). The highest concentrations of all investigated elements were found in the samples collected closest to the degassing craters, and in the downwind sector, confirming that the eastern flank of Mt. Etna is the most impacted by volcanic emissions. Leaves collected along two radial transects from the active vents on the eastern flank, highlight that the levels of metals decrease one or two orders of magnitude with increasing distance from the source. This variability is higher for volatile elements (As, Bi, Cd, Cs, Pb, Sb, Tl) than for more refractory elements (Al, Ba, Sc, Si, Sr, Th, U). The two different species of plants do not show significant differences in the bioaccumulation of most of the analyzed elements, except for lanthanides, which are systematically enriched in Rumex leaves. The high concentrations of many toxic elements in the leaves allow us to consider these plants as highly tolerant species to the volcanic emissions, and suitable for biomonitoring researches in the Mt. Etna area.

Description: Published

Description: Vienna, Austria

Description: 4.4. Scenari e mitigazione del rischio ambientale

Description: open

Description: Etna volcano, Italy, hosts one of the major groundwater systems of the island of Sicily. Waters circulate within highly permeable fractured, mainly hawaiitic, volcanic rocks. Aquifers are limited downwards by the underlying impermeable sedimentary terrains. Thickness of the volcanic rocks generally does not exceed some 300 m, preventing the waters to reach great depths. This is faced by short travel times (years to tens of years) and low thermalisation of the Etnean groundwaters. Measured temperatures are, in fact, generally lower than 25 °C. But the huge annual meteoric recharge (about 0.97 kmˆ3) with a high actual infiltration coefficient (0.75) implies a great underground circulation. During their travel from the summit area to the periphery of the volcano, waters acquire magmatic heat together with volcanic gases and solutes through water-rock interaction processes. In the last 20 years the Etnean aquifers has been extensively studied. Their waters were analysed for dissolved major, minor and trace element, O, H, C, S, B, Sr and He isotopes, and dissolved gas composition. These data have been published in several articles. Here, after a summary of the obtained results, the estimation of the magmatic heat flux through the aquifer will be discussed. To calculate heat uptake during subsurface circulation, for each sampling point (spring, well or drainage gallery) the following data have been considered: flow rate, water temperature, and oxygen isotopic composition. The latter was used to calculate the mean recharge altitude through the measured local isotopic lapse rate. Mean recharge temperatures, weighted for rain amount throughout the year, were obtained from the local weather station network. Calculations were made for a representative number of sampling points (216) including all major issues and corresponding to a total water flow of about 0.315 kmˆ3/a, which is 40% of the effective meteoric recharge. Results gave a total energy output of about 140 MW/a the half of which is ascribable to only 13 sampling points. These correspond to the highest flow drainage galleries with fluxes ranging from 50 to 1000 l/s and wells with pumping rates from 70 to 250 l/s. Geographical distribution indicates that, like magmatic gas leakage, heat flow is influenced by structural features of the volcanic edifice. The major heat discharge through groundwater are all tightly connected either to the major regional tectonic systems or to the major volcanic rift zones along which the most important flank eruptions take place. But rift zones are much more important for heat upraise due to the frequent dikes injection than for gas escape because generally when dikes have been emplaced the structure is no more permeable to gases because it becomes sealed by the cooling magma.

Description: Published

Description: Vienna, Austria

Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive

Description: open

Description: In order to investigate the impact of spatial resolution on the discrepancy between simulated δ18O and observed δ18O in Greenland ice cores, regional climate simulations are performed with the isotope-enabled regional climate model (RCM) COSMO_iso. For this purpose, isotope-enabled general circulation model (GCM) simulations with the ECHAM5-wiso general circulation model (GCM) under present-day conditions and the MPI-ESM-wiso GCM under mid-Holocene conditions are dynamically downscaled with COSMO_iso for the Arctic region. The capability of COSMO_iso to reproduce observed isotopic ratios in Greenland ice cores for these two periods is investigated by comparing the simulation results to measured δ18O ratios from snow pit samples, Global Network of Isotopes in Precipitation (GNIP) stations and ice cores. To our knowledge, this is the first time that a mid-Holocene isotope-enabled RCM simulation is performed for the Arctic region. Under present-day conditions, a dynamical downscaling of ECHAM5-wiso (1.1◦ × 1.1◦) with COSMO_iso to a spatial resolution of 50km improves the agreement with the measured δ18O ratios for 14 of 19 observational data sets. A further increase in the spatial resolution to 7km does not yield substantial improvements except for the coastal areas with its complex terrain. For the mid-Holocene, a fully coupled MPI-ESM-wiso time slice simulation is downscaled with COSMO_iso to a spatial resolution of 50km. In the mid-Holocene, MPI-ESM-wiso already agrees well with observations in Greenland and a downscaling with COSMO_iso does not further improve the model–data agreement. Despite this lack of improvement in model biases, the study shows that in both periods, observed δ18O values at measurement sites constitute isotope ratios which are mainly within the subgrid-scale variability of the global ECHAM5-wiso and MPI-ESM-wiso simulation results. The correct δ18O ratios are consequently not resolved in the GCM simulation results and need to be extracted by a refinement with an RCM. In this context, the RCM simulations provide a spatial δ18O distribution by which the effects of local uncertainties can be taken into account in the comparison between point measurements and model outputs. Thus, an isotope-enabled GCM–RCM model chain with realistically implemented fractionating processes constitutes a useful supplement to reconstruct regional paleo-climate conditions during the mid-Holocene in Greenland. Such model chains might also be applied to reveal the full potential of GCMs in other regions and climate periods, in which large deviations relative to observed isotope ratios are simulated.

Description: Proxy climate records are an invaluable source of information about the earth’s climate prior to the instrumental record. The temporal- and spatial-coverage of records continues to increase, however, these records of past climate are associated with significant uncertainties due to non-climate processes that influence the recorded and measured proxy values. Generally, these uncertainties are timescale-dependent and correlated in time. Accounting for structure in the errors is essential to providing realistic error estimates for smoothed or stacked records, detection of anomalies and identifying trends, but this structure is seldom accounted for. In the first of these companion articles we outlined a theoretical framework for handling proxy uncertainties by deriving the power spectrum of proxy error components from which it is possible to obtain timescale-dependent error estimates. Here in part II, we demonstrate the practical application of this theoretical framework using the example of marine sediment cores. We consider how to obtain estimates for the required parameters and give examples of the application of this approach for typical marine sediment proxy records. Our new approach of estimating and providing timescale-dependent proxy errors overcomes the limitations of simplistic single value error estimates. We aim to provide the conceptual basis for a more quantitative use of paleo-records for applications such as model-data comparison, regional and global synthesis of past climate states and data assimilation.

Description: The mid-Pliocene warm period (mPWP; ∼3.2 million years ago) is seen as the most recent time period characterized by a warm climate state, with similar to modern geography and ∼400 ppmv atmospheric CO2 concentration, and is therefore often considered an interesting analogue for near-future climate projections. Paleoenvironmental reconstructions indicate higher surface temperatures, decreasing tropical deserts, and a more humid climate in West Africa characterized by a strengthened West African Monsoon (WAM). Using model results from the second phase of the Pliocene Modelling Intercomparison Project (PlioMIP2) ensemble, we analyse changes of the WAM rainfall during the mPWP by comparing them with the control simulations for the pre-industrial period. The ensemble shows a robust increase in the summer rainfall over West Africa and the Sahara region, with an average increase of 2.5 mm/d, contrasted by a rainfall decrease over the equatorial Atlantic. An anomalous warming of the Sahara and deepening of the Saharan Heat Low, seen in 〉90 % of the models, leads to a strengthening of the WAM and an increased monsoonal flow into the continent. A similar warming of the Sahara is seen in future projections using both phase 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). Though previous studies of future projections indicate a west–east drying–wetting contrast over the Sahel, PlioMIP2 simulations indicate a uniform rainfall increase in that region in warm climates characterized by increasing greenhouse gas forcing. We note that this effect will further depend on the long-term response of the vegetation to the CO2 forcing.

Description: Due to its dryness, the subtropical free troposphere plays a critical role in the radiative balance of the Earth's climate system. But the complex interactions of the dynamical and physical processes controlling the variability in the moisture budget of this sensitive region of the subtropical atmosphere are still not fully understood. Stable water isotopes can provide important information about several of the latter processes, namely subsidence drying, turbulent mixing, and dry and moist convective moistening. In this study, we use high-resolution simulations of the isotope-enabled version of the regional weather and climate prediction model of the Consortium for Small-Scale Modelling (COSMOiso) to investigate predominant moisture transport pathways in the Canary Islands region in the eastern subtropical North Atlantic. Comparison of the simulated isotope signals with multi-platform isotope observations (aircraft, ground- and space-based remote sensing) from a field campaign in summer 2013 shows that COSMOiso can reproduce the observed variability of stable water vapour isotopes on timescales of hours to days, thus allowing us to study the mechanisms that control the subtropical free-tropospheric humidity. Changes in isotopic signals along backward trajectories from the Canary Islands region reveal the physical processes behind the synoptic-scale isotope variability. We identify four predominant moisture transport pathways of mid-tropospheric air, each with distinct isotopic signatures: - air parcels originating from the convective boundary layer of the Saharan heat low (SHL) – these are characterised by a homogeneous isotopic composition with a particularly high δD (median mid-tropospheric δD=−122‰), which results from dry convective mixing of low-level moisture of diverse origin advected into the SHL; - air parcels originating from the free troposphere above the SHL – although experiencing the largest changes in humidity and δD during their subsidence over West Africa, these air parcels typically have lower δD values (median δD=−148‰) than air parcels originating from the boundary layer of the SHL; - air parcels originating from outside the SHL region, typically descending from tropical upper levels south of the SHL, which are often affected by moist convective injections from mesoscale convective systems in the Sahel – their isotopic composition is much less enriched in heavy isotopes (median δD=−175‰) than those from the SHL region; - air parcels subsiding from the upper-level extratropical North Atlantic – this pathway leads to the driest and most depleted conditions (median δD=−255‰) in the middle troposphere near the Canary Islands. The alternation of these transport pathways explains the observed high variability in humidity and δD on synoptic timescales to a large degree. We further show that the four different transport pathways are related to specific large-scale flow conditions. In particular, distinct differences in the location of the North African mid-level anticyclone and of extratropical Rossby wave patterns occur between the four transport pathways. Overall, this study demonstrates that the adopted Lagrangian isotope perspective enhances our understanding of air mass transport and mixing and offers a sound interpretation of the free-tropospheric variability of specific humidity and isotope composition on timescales of hours to days in contrasting atmospheric conditions over the eastern subtropical North Atlantic.

Description: 〈b〉Intercultural interaction and "situational places": a perspective for urban cultural geography within and beyond the performative turn〈/b〉〈br〉 P. Dirksmeier and I. Helbrecht〈br〉 Soc. Geogr., 5, 39-48, doi:10.5194/sg-5-39-2010, 2010〈br〉 With the performative turn in social sciences and the humanities the concept of performance has arrived in human geography. Performance denotes an understanding of social actions and practices as constitutive for non-representational realities. This paper looks at the relationship between places and performance especially in urban geography and develops the new term "situational place" to grasp the increasing phenomenon of (intercultural) encounters in the cities of modern world society. "Situational places" are situated performances of these (intercultural) interactions between strangers in cities of the contemporary world society. With the aid of performance theory the influence of the omnipresent interactions between strangers in cities on urban space is conceptualized. Therewith, we hope to present some fruitful theoretical and empirical possibilities for a cultural urban geography within and beyond the performative turn.

Description: 〈b〉Déjà-vu: tourist practices of repeat visitors in the city of Paris〈/b〉〈br〉 T. Freytag〈br〉 Soc. Geogr., 5, 49-58, doi:10.5194/sg-5-49-2010, 2010〈br〉 In the context of sustained growth in European city tourism, competing travel destinations develop marketing strategies that include measures to attract an increasing number of repeat visitors. This paper explores the case of Paris in order to provide a better understanding of the specific motivations, interests and activities of leisure tourists who had previously stayed in the capital of France. Drawing on Pierre Bourdieu's concept of "distinction" it is argued that repeat visitors tend to differentiate themselves from other tourists. On the basis of substantive field work in Paris, a set of repeat visitor practices is presented that include strategies to avoid spatial concentrations of major tourist spots in order to participate in Parisian everyday life. Moreover, it is suggested to conceptualize the encounters between repeat visitors and tourism destinations as a lifelong relationship, which can be renewed and reproduced through further visits and virtual encounters. The distinct characteristics of repeat visitor practices have substantial implications for the organization of tourism in the city and the relationships between first-time tourists, repeat visitors and the local population.

Description: 〈b〉Intercultural interaction and "situational places": a perspective for urban cultural geography within and beyond the performative turn〈/b〉〈br〉 P. Dirksmeier and I. Helbrecht〈br〉 Soc. Geogr., 5, 39-48, doi:10.5194/sg-5-39-2010, 2010〈br〉 With the performative turn in social sciences and the humanities the concept of performance has arrived in human geography. Performance denotes an understanding of social actions and practices as constitutive for non-representational realities. This paper looks at the relationship between places and performance especially in urban geography and develops the new term "situational place" to grasp the increasing phenomenon of (intercultural) encounters in the cities of modern world society. "Situational places" are situated performances of these (intercultural) interactions between strangers in cities of the contemporary world society. With the aid of performance theory the influence of the omnipresent interactions between strangers in cities on urban space is conceptualized. Therewith, we hope to present some fruitful theoretical and empirical possibilities for a cultural urban geography within and beyond the performative turn.

Description: 〈b〉Plate tectonics conserves angular momentum〈/b〉〈br〉 C. Bowin〈br〉 eEarth, 5, 1-20, doi:10.5194/ee-5-1-2010, 2010〈br〉 A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4〈sup〉+27〈/sup〉 kg m〈sup〉2〈/sup〉 s〈sup〉−1〈/sup〉). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). 〈br〉〈br〉 Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies revealed by geoid anomalies of the degree 4–10 packet of the Earth's spherical harmonic coefficients. These linear positive geoid anomalies underlie plate subduction zones and are presumed due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. The magnitude of these sinking mass anomalies is inferred also to be sufficient to overcome basal plate and transform fault frictions. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. 〈br〉〈br〉 This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

Description: 〈b〉Déjà-vu: tourist practices of repeat visitors in the city of Paris〈/b〉〈br〉 T. Freytag〈br〉 Soc. Geogr., 5, 49-58, doi:10.5194/sg-5-49-2010, 2010〈br〉 In the context of sustained growth in European city tourism, competing travel destinations develop marketing strategies that include measures to attract an increasing number of repeat visitors. This paper explores the case of Paris in order to provide a better understanding of the specific motivations, interests and activities of leisure tourists who had previously stayed in the capital of France. Drawing on Pierre Bourdieu's concept of "distinction" it is argued that repeat visitors tend to differentiate themselves from other tourists. On the basis of substantive field work in Paris, a set of repeat visitor practices is presented that include strategies to avoid spatial concentrations of major tourist spots in order to participate in Parisian everyday life. Moreover, it is suggested to conceptualize the encounters between repeat visitors and tourism destinations as a lifelong relationship, which can be renewed and reproduced through further visits and virtual encounters. The distinct characteristics of repeat visitor practices have substantial implications for the organization of tourism in the city and the relationships between first-time tourists, repeat visitors and the local population.

Description: 〈b〉Plate tectonics conserves angular momentum〈/b〉〈br〉 C. Bowin〈br〉 eEarth, 5, 1-20, doi:10.5194/ee-5-1-2010, 2010〈br〉 A new combined understanding of plate tectonics, Earth internal structure, and the role of impulse in deformation of the Earth's crust is presented. Plate accelerations and decelerations have been revealed by iterative filtering of the quaternion history for the Euler poles that define absolute plate motion history for the past 68 million years, and provide an unprecedented precision for plate angular rotation variations with time at 2-million year intervals. Stage poles represent the angular rotation of a plate's motion between adjacent Euler poles, and from which the maximum velocity vector for a plate can be determined. The consistent maximum velocity variations, in turn, yield consistent estimates of plate accelerations and decelerations. The fact that the Pacific plate was shown to accelerate and decelerate, implied that conservation of plate tectonic angular momentum must be globally conserved, and that is confirmed by the results shown here (total angular momentum ~1.4〈sup〉+27〈/sup〉 kg m〈sup〉2〈/sup〉 s〈sup〉−1〈/sup〉). Accordingly, if a plate decelerates, other plates must increase their angular momentums to compensate. In addition, the azimuth of the maximum velocity vectors yields clues as to why the "bend" in the Emperor-Hawaiian seamount trend occurred near 46 Myr. This report summarizes processing results for 12 of the 14 major tectonic plates of the Earth (except for the Juan de Fuca and Philippine plates). 〈br〉〈br〉 Plate accelerations support the contention that plate tectonics is a product of torques that most likely are sustained by the sinking of positive density anomalies revealed by geoid anomalies of the degree 4–10 packet of the Earth's spherical harmonic coefficients. These linear positive geoid anomalies underlie plate subduction zones and are presumed due to phase changes in subducted gabbroic lithosphere at depth in the upper lower mantle (above 1200 km depth). The tectonic plates are pulled along by the sinking of these positive mass anomalies, rather than moving at near constant velocity on the crests of convection cells driven by rising heat. The magnitude of these sinking mass anomalies is inferred also to be sufficient to overcome basal plate and transform fault frictions. These results imply that spreading centers are primarily passive reactive features, and fracture zones (and wedge-shaped sites of seafloor spreading) are adjustment zones that accommodate strains in the lithosphere. Further, the interlocked pattern of the Australian and Pacific plates the past 42 Million years (with their absolute plate motions near 90° to each other) is taken as strong evidence that large thermally driven "roller" convection cells previously inferred as the driving mechanism in earlier interpretations of continental drift and plate tectonics, have not been active in the Earth's mantle the past 42 Million years, if ever. 〈br〉〈br〉 This report also presents estimates of the changes in location and magnitude of the Earth's axis of total plate tectonic angular momentum for the past 62 million years.

Description: Hyrrokkin sarcophaga is a parasitic foraminifera that is commonly found in cold-water coral reefs where it infests the file clam Acesta excavata and the scleractinian coral Desmophyllum pertusum (formerly known as Lophelia pertusa). Here, we present measurements of the trace element and isotopic composition of these parasitic foraminifera, analyzed by inductively coupled optical emission spectrometry (ICP-OES), electron probe microanalysis (EPMA) and mass spectrometry (gas-source MS and inductively-coupled-plasma MS). Our results reveal that the geochemical signature of H. sarcophaga depends on the host organism it infests. Sr / Ca ratios are 1.1 mmol mol−1 higher in H. sarcophaga that infest D. pertusum, which could be an indication that dissolved host carbonate material is utilized in shell calcification, given that the aragonite of D. pertusum has a naturally higher Sr concentration compared to the calcite of A. excavata. Similarly, we measure 3.1 ‰ lower δ13C and 0.25 ‰ lower δ18O values in H. sarcophaga that lived on D. pertusum, which might be caused by the direct uptake of the host's carbonate material with a more negative isotopic composition or different pH regimes in these foraminifera (pH can exert a control on the extent of CO2 hydration/hydroxylation) due to the uptake of body fluids of the host. We also observe higher Mn / Ca ratios in foraminifera that lived on A. excavata but did not penetrate the host shell compared to specimen that penetrated the shell, which could be interpreted as a change in food source, changes in the calcification rate, Rayleigh fractionation or changing oxygen conditions. While our measurements provide an interesting insight into the calcification process of this unusual foraminifera, these data also indicate that the geochemistry of this parasitic foraminifera is unlikely to be a reliable indicator of paleoenvironmental conditions using Sr / Ca, Mn / Ca, δ18O or δ13C unless the host organism is known and its geochemical composition can be accounted for.

Description: In this work we have performed a detailed study of vectors to ore to a representative volcanic-rock-hosted replacive volcanogenic massive sulfide (VMS) deposit located in the northern Iberian Pyrite Belt (Spain), the Aguas Teñidas deposit. The investigated vectors include the following: (1) mineralogical zoning, (2) host sequence characterization and mineralized unit identification based on whole rock geochemistry discrimination diagrams, (3) study of the characteristics and behaviour of whole rock geochemical anomalies around the ore (e.g. alteration-related compositional changes, characteristics and extent of geochemical halos of indicative elements such as Cu, Zn, Pb, Sb, Tl, and Ba around the deposit), and (4) application of portable X-ray fluorescence (p-XRF) analysis to the detection of the previous vectors. In the footwall, a concentric cone-shaped hydrothermal alteration zone bearing the stockwork passes laterally, from core to edge, from quartz (only local) to chlorite–quartz, sericite–chlorite–quartz, and sericite–quartz alteration zones. The hydrothermal alteration is also found in the hanging wall despite being tectonically allochthonous to the orebody: a proximal sericite alteration zone is followed by a more distal albite-rich one. Whole rock major elements show an increase in alteration indexes (e.g. AI, CCPI) towards the mineralization, a general SiO2 enrichment, and FeO enrichment as well as K2O and Na2O depletion towards the centre of the hydrothermal system, with MgO showing a less systematic behaviour. K2O and Na2O leached from the centre of the system are transported and deposited in more external areas. Copper, Pb, and Zn produce proximal anomalies around mineralized areas, with the more mobile Sb, Tl, and Ba generating wider halos. Whereas Sb and Tl halos form around all mineralized areas, Ba anomalies are restricted to areas around the massive sulfide body. Our results show that proposed vectors, or adaptations designed to overcome p-XRF limitations, can be confidently used by analysing unprepared hand specimens, including the external rough curved surface of drill cores. The data presented in this work are not only applicable to VMS exploration in the Iberian Pyrite Belt, but on a broader scale they will also contribute to improving our general understanding of vectors to ore in replacive-type VMS deposits.

Description: We combine satellite data products to provide a first and general overview of the physical sea ice conditions along the drift of the international Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition and a comparison with previous years (2005–2006 to 2018–2019). We find that the MOSAiC drift was around 20 % faster than the climatological mean drift, as a consequence of large-scale low-pressure anomalies prevailing around the Barents–Kara–Laptev sea region between January and March. In winter (October–April), satellite observations show that the sea ice in the vicinity of the Central Observatory (CO; 50 km radius) was rather thin compared to the previous years along the same trajectory. Unlike ice thickness, satellite-derived sea ice concentration, lead frequency and snow thickness during winter months were close to the long-term mean with little variability. With the onset of spring and decreasing distance to the Fram Strait, variability in ice concentration and lead activity increased. In addition, the frequency and strength of deformation events (divergence, convergence and shear) were higher during summer than during winter. Overall, we find that sea ice conditions observed within 5 km distance of the CO are representative for the wider (50 and 100 km) surroundings. An exception is the ice thickness; here we find that sea ice within 50 km radius of the CO was thinner than sea ice within a 100 km radius by a small but consistent factor (4 %) for successive monthly averages. Moreover, satellite acquisitions indicate that the formation of large melt ponds began earlier on the MOSAiC floe than on neighbouring floes.

Description: Across the Qinghai–Tibet Plateau (QTP) there is a narrow engineering corridor with widely distributed slopes called the Qinghai–Tibet Engineering Corridor (QTEC), where a variety of important infrastructures are concentrated. These facilities are transportation routes for people, materials, energy, etc. from inland China to the Tibet Autonomous Region. From Golmud to Lhasa, the engineering corridor covers 632 km of permafrost containing the densely developed Qinghai–Tibet Railway and Qinghai–Tibet Highway, as well as power and communication towers. Slope failure in permafrost regions, caused by permafrost degradation, ground ice melting, etc., affects the engineering construction and permafrost environments in the QTEC. We implement a variety of sensors to monitor the hydrological and thermal deformation between permafrost slopes and permafrost engineering projects in the corridor. In addition to soil temperature and moisture sensors, the global navigation satellite system (GNSS), terrestrial laser scanning (TLS), and unmanned aerial vehicles (UAVs) were adopted to monitor the spatial distribution and changes in thermal deformation. An integrated dataset of hydrological and thermal deformation in permafrost engineering and slopes in the QTEC from the 1950s to 2020, including meteorological and ground observations, TLS point cloud data, and RGB and thermal infrared (TIR) images, can be of great value for estimating the hydrological and thermal impact and stability between engineering and slopes under the influence of climate change and engineering disturbance. The dataset and code were uploaded to the Zenodo repository and can be accessed through https://zenodo.org/communities/qtec (last access: 23 June 2021), including meteorological and ground observations at https://doi.org/10.5281/zenodo.5009871 (Luo et al., 2020d), TLS measurements at https://doi.org/10.5281/zenodo.5009558 (Luo et al., 2020a), UAV RGB and TIR images at https://doi.org/10.5281/zenodo.5016192 (Luo et al., 2020b), and R code for permafrost indices and visualisation at https://doi.org/10.5281/zenodo.5002981 (Luo et al., 2020c).

Description: We present the first incorporation of the Common Representative Intermediates version 2.2 tropospheric chemistry mechanism, CRI v2.2, combined with stratospheric chemistry, into the global chemistry–climate United Kingdom Chemistry and Aerosols (UKCA) model to give the CRI-Strat 2 mechanism. A rigorous comparison of CRI-Strat 2 with the earlier version, CRI-Strat, is performed in UKCA in addition to an evaluation of three mechanisms, CRI-Strat 2, CRI-Strat and the standard UKCA chemical mechanism, StratTrop v1.0, against a wide array of surface and airborne chemical data. CRI-Strat 2 comprises a state-of-the-art isoprene scheme, optimized against the Master Chemical Mechanism v3.3.1, which includes isoprene peroxy radical isomerization, HOx recycling through the addition of photolabile hydroperoxy aldehydes (HPALDs), and isoprene epoxy diol (IEPOX) formation. CRI-Strat 2 also features updates to several rate constants for the inorganic chemistry, including the reactions of inorganic nitrogen and O(1D). The update to the isoprene chemistry in CRI-Strat 2 increases OH over the lowest 500 m in tropical forested regions by 30 %–50 % relative to CRI-Strat, leading to an improvement in model–observation comparisons for surface OH and isoprene relative to CRI-Strat and StratTrop. Enhanced oxidants also cause a 25 % reduction in isoprene burden and an increase in oxidation fluxes of isoprene and other biogenic volatile organic compounds (BVOCs) at low altitudes with likely impacts on subsequent aerosol formation, atmospheric lifetime, and climate. By contrast, updates to the rate constants of O(1D) with its main reactants relative to CRI-Strat reduces OH in much of the free troposphere, producing a 2 % increase in the methane lifetime, and increases the tropospheric ozone burden by 8 %, primarily from reduced loss via O(1D)+H2O. The changes to inorganic nitrogen reaction rate constants increase the NOx burden by 4 % and shift the distribution of nitrated species closer to that simulated by StratTrop. CRI-Strat 2 is suitable for multi-decadal model integrations and the improved representation of isoprene chemistry provides an opportunity to explore the consequences of HOx recycling in the United Kingdom Earth System Model (UKESM1). This new mechanism will enable a re-evaluation of the impact of BVOCs on the chemical composition of the atmosphere and further probe the feedback between the biosphere and the climate.

Description: The use of mass flow simulations in volcanic hazard zonation and mapping is often limited by model complexity (i.e. uncertainty in correct values of model parameters), a lack of model uncertainty quantification, and limited approaches to incorporate this uncertainty into hazard maps. When quantified, mass flow simulation errors are typically evaluated on a pixel-pair basis, using the difference between simulated and observed (“actual”) map-cell values to evaluate the performance of a model. However, these comparisons conflate location and quantification errors, neglecting possible spatial autocorrelation of evaluated errors. As a result, model performance assessments typically yield moderate accuracy values. In this paper, similarly moderate accuracy values were found in a performance assessment of three depth-averaged numerical models using the 2012 debris avalanche from the Upper Te Maari crater, Tongariro Volcano, as a benchmark. To provide a fairer assessment of performance and evaluate spatial covariance of errors, we use a fuzzy set approach to indicate the proximity of similarly valued map cells. This “fuzzification” of simulated results yields improvements in targeted performance metrics relative to a length scale parameter at the expense of decreases in opposing metrics (e.g. fewer false negatives result in more false positives) and a reduction in resolution. The use of this approach to generate hazard zones incorporating the identified uncertainty and associated trade-offs is demonstrated and indicates a potential use for informed stakeholders by reducing the complexity of uncertainty estimation and supporting decision-making from simulated data.

Description: In this study, we analyse the climatology of ionosphere over Nepal based on GPS-derived vertical total electron content (VTEC) observed from four stations as defined in Table 1: KKN4 (27.80∘ N, 85.27∘ E), GRHI (27.95∘ N, 82.49∘ E), JMSM (28.80∘ N, 83.74∘ E) and DLPA (28.98∘ N, 82.81∘ E) during the years 2008 to 2018. The study illustrates the diurnal, monthly, annual, seasonal and solar cycle variations in VTEC during all times of solar cycle 24. The results clearly reveal the presence of equinoctial asymmetry in TEC, which is more pronounced in maximum phases of solar cycle in the year 2014 at KKN4 station, followed by descending, ascending and minimum phases. Diurnal variations in VTEC showed the short-lived day minimum which occurs between 05:00 to 06:00 LT (local time) at all the stations considered, with diurnal peaks between 12:00 and 15:00 LT. The maximum value of TEC is observed more often during the spring equinox than the autumn equinox, with a few asymmetries. Seasonal variation in TEC is observed to be a manifestation of variations in solar flux, particularly regarding the level of solar flux in consecutive solstices.

Description: We report on applications of the ultraviolet-light-emitting-diode-based incoherent broadband cavity-enhanced absorption spectroscopy (UV-LED-IBBCEAS) technique for optical monitoring of HONO, NO2 and CH2O in a simulation chamber. Performance intercomparison of UV-LED-IBBCEAS with a wet chemistry-based NitroMAC sensor and a Fourier transform infrared (FTIR) spectrometer has been carried out on real-time simultaneous measurement of HONO, NO2 and CH2O concentrations during the reaction of NO2 with H2O vapour in CESAM (French acronym for Experimental Multiphasic Atmospheric Simulation Chamber). The 1σ (signal-to-noise ratio (SNR) = 1) detection limits of 112 pptv for NO2, 56 pptv for HONO and 41 ppbv for CH2O over 120 s were found for the UV-LED-IBBCEAS measurement. On the contrary to many set-ups where cavities are installed outside the simulation chamber, we describe here an original in situ permanent installation. The intercomparison results demonstrate that IBBCEAS is a very well suitable technique for in situ simultaneous measurements of multiple chemically reactive species with high sensitivity and high precision even if the absorption bands of these species are overlapped. It offers excellent capacity for non-invasive optical monitoring of chemical reactions without any perturbation. For the application to simulation chambers, it has the advantage to provide a spatially integrated measurement across the reactor and hence to avoid point-sampling-related artefacts.

Description: Assimilation of weather radar measurements including radar reflectivity and radial wind data has been operational at the Deutscher Wetterdienst, with a diagonal observation error (OE) covariance matrix. For an implementation of a full OE covariance matrix, the statistics of the OE have to be a priori estimated, for which the Desroziers method has been often used. However, the resulted statistics consists of contributions from different error sources and are difficult to interpret. In this work, we use an approach that is based on samples for truncation error in radar observation space to approximate the representation error due to unresolved scales and processes (RE) and compare its statistics with the OE statistics estimated by the Desroziers method. It is found that the statistics of the RE help the understanding of several important features in the variances and correlation length scales of the OE for both reflectivity and radial wind data and the other error sources from the microphysical scheme, radar observation operator and the superobbing technique may also contribute, for instance, to differences among different elevations and observation types. The statistics presented here can serve as a guideline for selecting which observations are assimilated and for assignment of the OE covariance matrix that can be diagonal or full and correlated.

Description: Determining controls on the temperature sensitivity of heterotrophic soil respiration remains critical to incorporating soil–climate feedbacks into climate models. Most information on soil respiratory responses to temperature comes from laboratory incubations of isolated soils and typically subsamples of individual horizons. Inconsistencies between field and laboratory results may be explained by microbial priming supported by cross-horizon exchange of labile C or N. Such exchange is feasible in intact soil profiles but is absent when soils are isolated from surrounding depths. Here we assess the role of soil horizon connectivity, by which we mean the degree to which horizons remain layered and associated with each other as they are in situ, on microbial C and N substrate use and its relationship to the temperature sensitivity of respiration. We accomplished this by exploring changes in C : N, soil organic matter composition (via C : N, amino acid composition and concentration, and nuclear magnetic resonance spectroscopy), and the δ13C of respiratory CO2 during incubations of organic horizons collected across boreal forests in different climate regions where soil C and N compositions differ. The experiments consisted of two treatments: soil incubated (1) with each organic horizon separately and (2) as a whole organic profile, permitting cross-horizon exchange of substrates during the incubation. The soils were incubated at 5 and 15 ∘C for over 430 d. Enhanced microbial use of labile C-rich, but not N-rich, substrates were responsible for enhanced, whole-horizon respiratory responses to temperature relative to individual soil horizons. This impact of a labile C priming mechanism was most emergent in soils from the warmer region, consistent with these soils' lower C bioreactivity relative to soils from the colder region. Specifically, cross-horizon exchange within whole soil profiles prompted increases in mineralization of carbohydrates and more 13C-enriched substrates and increased soil respiratory responses to warming relative to soil horizons incubated in isolation. These findings highlight that soil horizon connectivity can impact microbial substrate use in ways that affect how soil effluxes of CO2 are controlled by temperature. The degree to which this mechanism exerts itself in other soils remains unknown, but these results highlight the importance of understanding mechanisms that operate in intact soil profiles – only rarely studied – in regulating a key soil–climate feedback.

Description: Plumes from the boreal spring biomass burning (BB) in northern peninsular Southeast Asia (nPSEA) are lifted into the subtropical jet stream and transported and deposited across nPSEA, South China, Taiwan and even the western North Pacific Ocean. This paper as part of the Seven SouthEast Asian Studies (7-SEAS) project effort attempts to improve the chemical weather prediction capability of the Weather Research and Forecasting coupled with the Community Multiscale for Air Quality (WRF–CMAQ) model over a vast region, from the mountainous near-source burning sites at nPSEA to its downwind region. Several sensitivity analyses of plume rise are compared in the paper, and it is discovered that the initial vertical allocation profile of BB plumes and the plume rise module (PLMRIM) are the main reasons causing the inaccuracies of the WRF–CMAQ simulations. The smoldering emission from the Western Regional Air Partnership (WRAP) empirical algorithm included has improved the accuracies of PM10, O3 and CO at the source. The best performance at the downwind sites is achieved with the inline PLMRIM, which accounts for the atmospheric stratification at the mountainous source region with the FINN burning emission dataset. Such a setup greatly improves not only the BB aerosol concentration prediction over near-source and receptor ground-based measurement sites but also the aerosol vertical distribution and column aerosol optical depth of the BB aerosol along the transport route. The BB aerosols from nPSEA are carried by the subtropical westerlies in the free troposphere to the western North Pacific, while BB aerosol has been found to interact with the local pollutants in the Taiwan region through three conditions: (a) overpassing western Taiwan and entering the central mountain area, (b) mixing down to western Taiwan, (c) transport of local pollutants upwards and mixing with a BB plume on higher ground. The second condition, which involves the prevailing high-pressure system from Asian cold surge, is able to impact most of the population in Taiwan.

Description: The German Bight located within the central North Sea is a hydro- and morphodynamically highly complex system of estuaries, barrier islands, and part of the world's largest coherent tidal flats, the Wadden Sea. To identify and understand challenges faced by coastal stakeholders, such as harbor operators or governmental agencies, to maintain waterways and employ numerical models for further analyses, it is imperative to have a consistent database for both bathymetry and surface sedimentology. Current commercial and public data products are insufficient in spatial and temporal resolution and coverage for recent analysis methods. Thus, this first part of a two-part publication series of the German joint project EasyGSH-DB describes annual bathymetric digital terrain models at a 10 m gridded resolution for the German North Sea coast and German Bight from 1996 to 2016 (Sievers et al., 2020a, https://doi.org/10.48437/02.2020.K2.7000.0001), as well as surface sedimentological models of discretized cumulative grain size distribution functions for 1996, 2006, and 2016 on 100 m grids (Sievers et al., 2020b, https://doi.org/10.48437/02.2020.K2.7000.0005). Furthermore, basic morphodynamic and sedimentological processing analyses, such as the estimation of, for example, bathymetric stability or surface maps of sedimentological parameters, are provided (Sievers et al., 2020a, b, see respective download links).

Description: The Phanerozoic tectonothermal evolution of the SW slope of the East European Platform (EEP) in Poland is reconstructed by means of thermal maturity, low-temperature thermochronometry, and thermal modelling. We provide a set of new thermochronometric data and integrate stratigraphic and thermal maturity information to constrain the burial and thermal history of sediments. Apatite fission track (AFT) analysis and zircon (U-Th)/He (ZHe) thermochronology have been carried out on samples of sandstones, bentonites, diabase, and crystalline basement rocks collected from 17 boreholes located in central and NE Poland. They penetrated sedimentary cover of the EEP subdivided from the north to south into the Baltic, Podlasie, and Lublin basins. The average ZHe ages from Proterozoic basement rocks as well as Ordovician to Silurian bentonites and Cambrian to lower Carboniferous sandstones range from 848 ± 81 to 255 ± 22 Ma with a single early Permian age of 288 Ma, corresponding to cooling after a thermal event. The remaining ZHe ages represent partial reset or source ages. The AFT ages of samples are dispersed in the range of 235.8 ± 17.3 Ma (Middle Triassic) to 42.1 ± 11.1 Ma (Paleogene) providing a record of Mesozoic and Cenozoic cooling. The highest frequency of the AFT ages is in the Jurassic and Early Cretaceous prior to Alpine basin inversion. Thermal maturity results are consistent with the SW-ward increase of the Paleozoic and Mesozoic sediments thickness. An important break in a thermal maturity profile exists across the base Permian–Mesozoic unconformity. Thermal modelling showed that significant heating of Ediacaran to Carboniferous sedimentary successions occurred before the Permian with maximum paleotemperatures in the earliest and latest Carboniferous for Baltic–Podlasie and Lublin basins, respectively. The results obtained suggest an important role of early Carboniferous uplift and exhumation at the SW margin of the EEP. The SW slope of the latter was afterward overridden in the Lublin Basin by the Variscan orogenic wedge. Its tectonic loading interrupted Carboniferous uplift and caused resumption of sedimentation in the late Viséan. Consequently, a thermal history of the Lublin Basin is different from that in the Podlasie and Baltic basins but similar to other sections of the Variscan foreland, characterized by maximum burial at the end of Carboniferous. The Mesozoic thermal history was characterized by gradual cooling from peak temperatures at the transition from Triassic to Jurassic due to decreasing heat flow. Burial caused maximum paleotemperatures in the SW part of the study area, where the EEP was covered by an extensive sedimentary pile. However, further NE, due to low temperatures caused by shallow burial, the impact of fluids can be detected by vitrinite reflectance, illite/smectite, and thermochronological data. Our new results emphasize the importance of using multiple low-temperature thermochronometers and thermal modelling in connection with thermal maturity analysis to elucidate the near-surface evolution of platform margins.

Description: Snow stands out from materials at the Earth’s surface owing to its unique optical properties. Snow optical properties are sensitive to the snow microstructure, triggering potent climate feedbacks. The impacts of snow microstructure on its optical properties such as reflectance are, to date, only partially understood. However, precise modelling of snow reflectance, particularly bidirectional reflectance, are required in many problems, e.g. to correctly process satellite data over snow-covered areas. This study presents a dataset that combines bidirectional reflectance measurements over 500–2500 nm and the X-ray tomography of the snow microstructure for three snow samples of two different morphological types. The dataset is used to evaluate the stereological approach from Malinka (2014) that relates snow optical properties to the chord length distribution in the snow microstructure. The mean chord length and specific surface area (SSA) retrieved with this approach from the albedo spectrum and those measured by the X-ray tomography are in excellent agreement. The analysis of the 3D images has shown that the random chords of the ice phase obey the gamma distribution with the shape parameter m taking the value approximately equal to or a little greater than 2. For weak and intermediate absorption (high and medium albedo), the simulated bidirectional reflectances reproduce the measured ones accurately but tend to slightly overestimate the anisotropy of the radiation. For such absorptions the use of the exponential law for the ice chord length distribution instead of the one measured with the X-ray tomography does not affect the simulated reflectance. In contrast, under high absorption (albedo of a few percent), snow microstructure and especially facet orientation at the surface play a significant role in the reflectance, particularly at oblique viewing and incidence.

Description: Attribution in its general definition aims to quantify drivers of change in a system. According to IPCC Working Group II (WGII) a change in a natural, human or managed system is attributed to climate change by quantifying the difference between the observed state of the system and a counterfactual baseline that characterizes the system's behavior in the absence of climate change, where “climate change refers to any long-term trend in climate, irrespective of its cause” (IPCC, 2014). Impact attribution following this definition remains a challenge because the counterfactual baseline, which characterizes the system behavior in the hypothetical absence of climate change, cannot be observed. Process-based and empirical impact models can fill this gap as they allow us to simulate the counterfactual climate impact baseline. In those simulations, the models are forced by observed direct (human) drivers such as land use changes, changes in water or agricultural management but a counterfactual climate without long-term changes. We here present ATTRICI (ATTRIbuting Climate Impacts), an approach to construct the required counterfactual stationary climate data from observational (factual) climate data. Our method identifies the long-term shifts in the considered daily climate variables that are correlated to global mean temperature change assuming a smooth annual cycle of the associated scaling coefficients for each day of the year. The produced counterfactual climate datasets are used as forcing data within the impact attribution setup of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a). Our method preserves the internal variability of the observed data in the sense that factual and counterfactual data for a given day have the same rank in their respective statistical distributions. The associated impact model simulations allow for quantifying the contribution of climate change to observed long-term changes in impact indicators and for quantifying the contribution of the observed trend in climate to the magnitude of individual impact events. Attribution of climate impacts to anthropogenic forcing would need an additional step separating anthropogenic climate forcing from other sources of climate trends, which is not covered by our method.

Description: Biocides used in film protection products leaching from facades are known to be a potential threat to the environment. This study identifies individual sources and entry pathways in a small-scale urban area. We investigate emissions of commonly used biocides (terbutryn, diuron, and octylisothiazolinone – OIT) and some of their transformation products (TPs; diuron-desmethyl, terbumeton, terbuthylazine-2-hydroxy, and terbutryn-desethyl) from a 2 ha residential area 13 years after construction has ended. Sampling utilizes existing urban water infrastructure representative for decentralized storm water management in central and northern Europe and applies a two-step approach to (a) determine the occurrence of biocides above water quality limits (i.e., predicted no-effect concentration, PNEC) and (b) identify source areas and characterize entry pathways into surface and groundwater. Monitoring focuses on the analysis of selected biocides and TPs by liquid chromatography–mass spectrometry/mass spectrometry (LC-MS/MS) in water samples taken from facades, rainwater pipes, drainage, and storm water infiltration systems. In standing water in a swale, we found high concentrations of diuron (174 ng L−1) and terbutryn (40 ng L−1) above PNEC for surface water. We confirmed expected sources, i.e., facades. Sampling of rain downpipes from flat roofs identified additional sources of all biocides and two TPs of terbutryn and one TP of diuron. Diuron and terbutryn were found in three drainage pipes representing different entry pathways of biocides. In one drainage pipe collecting road runoff, only diuron-desmethyl and terbutryn-desethyl were detected. In two other drainage pipes collecting infiltrated water through soil, terbuthylazine-2-hydroxy was additionally detected. One of the pipes collecting infiltrated water through soil concentration showed the highest concentrations of terbutryn and two of its TPs (terbutryn-desethyl and terbuthylazine-2-hydroxy). This suggests a high leaching potential of terbutryn. The applied two-step approach determined sources and pathways of biocide and their TPs. This study contributes to expanding knowledge on their entry and distribution and, thus, eventually towards reducing emissions.

Description: Regional anomalies of steric sea level are either due to redistribution of heat and freshwater anomalies or due to ocean–atmosphere buoyancy fluxes. Interannual to decadal variability in sea level across the tropical Pacific is mainly due to steric variations driven by wind stress anomalies. The importance of air–sea buoyancy fluxes is less clear. We use a global, eddy-permitting ocean model and a series of sensitivity experiments with quasi-climatological momentum and buoyancy fluxes to identify the contribution of buoyancy fluxes for interannual to decadal sea level variability in the tropical Pacific. We find their contribution on interannual timescales to be strongest in the central tropical Pacific at around a 10∘ latitude in both hemispheres and also relevant in the very east of the tropical domain. Buoyancy-flux-forced anomalies are correlated with variations driven by wind stress changes, but their effect on the prevailing anomalies and the importance of heat and freshwater fluxes vary locally. In the eastern tropical basin, interannual sea level variability is amplified by anomalous heat fluxes, while the importance of freshwater fluxes is small, and neither has any impact on decadal timescales. In the western tropical Pacific, the variability on interannual and decadal timescales is dampened by both heat and freshwater fluxes. The mechanism involves westward-propagating Rossby waves that are triggered during El Niño–Southern Oscillation (ENSO) events by anomalous buoyancy fluxes in the central tropical Pacific and counteract the prevailing sea level anomalies once they reach the western part of the basin.

Description: The Nioghalvfjerdsfjorden glacier (also known as the 79∘ North Glacier) drains approximately 8 % of the Greenland Ice Sheet. Supraglacial lakes (SGLs), or surface melt ponds, are a persistent summertime feature and are thought to drain rapidly to the base of the glacier and influence seasonal ice velocity. However, seasonal development and spatial distribution of SGLs in the north-east of Greenland are poorly understood, leaving a substantial error in the estimate of meltwater and its impacts on ice velocity. Using results from an automated detection of melt ponds, atmospheric and surface mass balance modelling, and reanalysis products, we investigate the role of specific climatic conditions in melt onset, extent, and duration from 2016 to 2019. The summers of 2016 and 2019 were characterised by above-average air temperatures, particularly in June, as well as a number of rainfall events, which led to extensive melt ponds to elevations up to 1600 m. Conversely, 2018 was particularly cold, with a large accumulated snowpack, which limited the development of lakes to altitudes less than 800 m. There is evidence of inland expansion and increases in the total area of lakes compared to the early 2000s, as projected by future global warming scenarios.

Description: Coincident wide-angle and multi-channel seismic data acquired within the scope of the PAMELA Moz3-5 project allow us to reconsider the formation mechanism of East African margins offshore of southern Mozambique. This study specifically focuses on the sedimentary and deep-crustal architecture of the Limpopo margin (LM) that fringes the eastern edge of the Mozambique’s Coastal Plain (MCP) and its offshore southern prolongation the North Natal Valley (NNV). It relies primarily on the MZ3 profile that runs obliquely from the northeastern NNV towards the Mozambique basin (MB) with additional inputs from a tectonostratigraphy analysis of industrial onshore–offshore seismic lines and nearby or crossing velocity models from companion studies. Over its entire N–S extension the LM appears segmented into (1) a western domain that shows the progressive eastward crustal thinning and termination of the MCP/NNV continental crust and its overlying pre-Neocomian volcano-sedimentary basement and (2) a central corridor of anomalous crust bounded to the east by the Mozambique fracture zone (MFZ) and the oceanic crust of the MB. A prominent basement high marks the boundary between these two domains. Its development was most probably controlled by a steep and deeply rooted fault, i.e., the Limpopo fault. We infer that strike-slip or slightly transtensional rifting occurred along the LM and was accommodated along this Limpopo fault. At depth we propose that ductile shearing was responsible for the thinning of the continental crust and an oceanward flow of lower crustal material. This process was accompanied by intense magmatism that extruded to form the volcanic basement and gave the corridor its peculiar structure and mixed nature. The whole region remained at a relative high level during the rifting period and a shallow marine environment dominated the pre-Neocomian period during the early phase of continent–ocean interaction. It is only some time after break-up in the MB and the initiation of the MFZ that decoupling occurred between the MCP/NNV and the corridor, allowing for the latter to subside and become covered by deep marine sediments. A scenario for the early evolution and formation of the LM is proposed taking into account both recent kinematic and geological constraints. It implies that no or little change in extensional direction occurred between the intra-continental rifting and subsequent phase of continent–ocean interaction.

Description: Models are an important tool to predict Earth system dynamics. An accurate prediction of future states of ecosystems depends on not only model structures but also parameterizations. Model parameters can be constrained by data assimilation. However, applications of data assimilation to ecology are restricted by highly technical requirements such as model-dependent coding. To alleviate this technical burden, we developed a model-independent data assimilation (MIDA) module. MIDA works in three steps including data preparation, execution of data assimilation, and visualization. The first step prepares prior ranges of parameter values, a defined number of iterations, and directory paths to access files of observations and models. The execution step calibrates parameter values to best fit the observations and estimates the parameter posterior distributions. The final step automatically visualizes the calibration performance and posterior distributions. MIDA is model independent, and modelers can use MIDA for an accurate and efficient data assimilation in a simple and interactive way without modification of their original models. We applied MIDA to four types of ecological models: the data assimilation linked ecosystem carbon (DALEC) model, a surrogate-based energy exascale earth system model: the land component (ELM), nine phenological models and a stand-alone biome ecological strategy simulator (BiomeE). The applications indicate that MIDA can effectively solve data assimilation problems for different ecological models. Additionally, the easy implementation and model-independent feature of MIDA breaks the technical barrier of applications of data–model fusion in ecology. MIDA facilitates the assimilation of various observations into models for uncertainty reduction in ecological modeling and forecasting.

Description: One year of multi-wavelength (3+2) Raman lidar measurements at Gual Pahari, close to Delhi, were analysed. The data was split into four seasons: spring (March–May), summer (June–August), autumn (September–November) and winter (December–February). The vertical profiles of backscatter, extinction, and lidar ratio and their variability during each season are presented. The measurements revealed that, on average, the aerosol layer was at its highest in spring (5.5 km). In summer, the vertically averaged (between 1–3 km) backscatter and extinction coefficients had the highest averages (3.3 Mm−1 sr−1 and 142 Mm−1 at 532 nm, respectively). Aerosol concentrations were slightly higher in summer compared with other seasons, and particles were larger in size. The autumn showed the highest lidar ratio and high extinction-related Ångström exponents (AEext), indicating the presence of smaller probably absorbing particles. The winter had the lowest backscatter and extinction coefficients, but AEext was the highest, suggesting still a large amount of small particles.

Description: The formation of organic nitrates and secondary organic aerosol (SOA) were monitored during the NO3 + limonene reaction in the atmosphere simulation chamber SAPHIR at Research Center Jülich. The 24-h run began in a purged, dry, particle-free chamber and comprised two injections of limonene and oxidants, such that the first experiment measured SOA yield in the absence of seed aerosol, and the second experiment yields in the presence of 10 μg m−3 seed organic aerosol. After each injection, two separate increases in aerosol mass were observed, corresponding to sequential oxidation of the two limonene double bonds. Analysis of the measured NO3, limonene, product nitrate concentrations, and aerosol properties provides mechanistic insight and constrains rate constants, branching ratios and vapor pressures of the products. The organic nitrate yield from NO3 + limonene is ≈30%. The SOA mass yield was observed to be 25–40%. The first injection is reproduced by a kinetic model. PMF analysis of the aerosol composition suggests that much of the aerosol mass results from combined oxidation by both O3 and NO3, e.g., oxidation of NO3 + limonene products by O3. Further, later aerosol nitrate mass seems to derive from heterogeneous uptake of NO3 onto unreacted aerosol alkene.

Description: The radiative forcing estimation of the polluted mineral dust is limited due to lack of morphological analysis, mixing state with the carbonaceous components and the hematite content in the pure dust. The accumulation mode mineral dust has been found to mix with anthropogenically produced black carbon, organic carbon and brown carbon during long range transport. The above features of the polluted dust are not well accounted in the optical models and lead the uncertainty in the numerical estimation of their radiative impact. The Semi-external mixing being a prominent mixing of dust and carbonaceous components has not been studied in details so for compared to core-shell, internal and external mixing studies. In present study, we consider the pure mineral dust composed of non-metallic components (such as Quartz, Feldspar, Mica and Calcite) and metalic component like hematite (Fe2O3). The hematite percentage in the pure mineral dust governs its absorbance. Based on this hematite variation, the hematite fraction in pure mineral dust has been constrained between 0–8%. The morphological and mineralogical characterization of the polluted dust led to consider the three sphere, two sphere and two spheroid model shapes for polluted dust particle system. The pollution gives rise to various light absorbing aerosol components like black carbon, brown carbon and organic carbon (comprising of HUmic-Like Substances, HULIS) in the atmosphere. The entire above discussed model shapes have been considered for the mineral dust getting polluted with (1) organic carbon (especially HULIS component) (2) Brown carbon and (3) black carbon by making a semi-external mixture with pure mineral dust. The optical properties (like Single Scattering Albedo, SSA; Asymmetry parameter, g and Extinction efficiency, Qext) of above model shapes for the polluted dust have been computed using Discrete Dipole Approximation, DDA code. For above model shapes, the SSA was found to vary depending on hematite content (0–8%) and model shape composition. For the two sphere BC-mineral dust cluster, hematite was found to be dominating absorber compared to that of black carbon as the RBC/Rdust decreases. (i.e. with increase of dust sphere size compared to black carbon sphere in the composite 2-sphere cluster). SSA was found to be very sensitivity for the hematite content when both of the spheres (i.e. mineral dust and BC) are nearly of same size. The two spheroid system composed of organic carbon and dust with 0% hematite (OCD'-0) showed the maximum deviation of SSA (i.e.~5%) compared to the two sphere system of same composition and hematite content (OCD-0 ). Increase in hematite from 0 to 8% caused maximum SSA deviation of ~20% for two sphere organic carbon-dust system (OCD) while the same has been observed to be ~18% for two spheroid organic carbon-dust system (OCD'). SSA was found to be more sensitive to hematite content than that of particle shape. Compared to SSA, Asymmetry parameter, g was found to be more sensitive towards particle shape. For three-sphere model shapes with 0% hematite composed of black carbon-dust-dust (BCDD-0), brown carbon-dust-dust (BrCDD-0 ) and organic carbon-dust-dust (OCDD-0), the deviation of SSA and g relative to conjugate black carbon (BC), brown carbon (BrC) and organic carbon (OC) spheres are ~68% and ~31%, ~83% and ~31% and ~70% and ~33%, respectively. Thus modeled polluted dust optics will provide a better basis for radiative forcing estimation and many sensitivity studies.

Description: A plume rise algorithm for wildfires was included in WRF-Chem, and applied to look at the impact of intense wildfires during the 2004 Alaska wildfire season on weather simulations using model resolutions of 10 km and 2 km. Biomass burning emissions were estimated using a biomass burning emissions model. In addition a 1-D time dependent cloud model was used online in WRF-Chem to estimate injection heights as well as the final emission rates. It was shown that with the inclusion of the intense wildfires of the 2004 fire season in the model simulations the interaction of the aerosols with the atmospheric radiation lead to significant modifications of vertical profiles of temperature and moisture in cloud-free areas. On the other hand, when clouds were present, the high concentrations of fine aerosol (PM2.5) and the resulting large numbers of Cloud Condensation Nuclei (CCN) had a strong impact on clouds and microphysics, with decreased precipitation coverage and precipitation amounts during the first 12 h of the integration, but significantly stronger storms during the afternoon hours.

Description: This study is based on 18 months (20 July 2006–5 February 2008) of continuous measurements of aerosol particle size distributions, air ion size distributions, trace gas concentrations and basic meteorology in a semi-clean savannah environment in Republic of South Africa. New particle formation and growth was observed on 69% of the days and bursts of non-growing ions/sub-10 nm particles on additional 14% of the days. The new particle formation and growth rates were among the highest reported in the literature for continental boundary layer locations; median 10 nm formation rate was 2.2 cm−3s−1 and median 10–30 nm growth rate 8.9 nm h−1. The median 2 nm ion formation rate was 0.5 cm−3s−1 and the median ion growth rates were 6.2, 8.0 and 8.1 nm h−1 for size ranges 1.5–3 nm, 3–7 nm and 7–20 nm, respectively. Three different approaches were used to study the origin of the formation and growth rates: seasonal variation, air mass history analysis and estimated sulphuric acid contribution to the growth. The growth rates had a clear seasonal dependency with minimum during winter and maxima in spring and late summer and the air mass history analysis indicated the highest formation and growth rates to be associated with the area of highest VOC (Volatile Organic Compounds) emissions rather than the highest estimated sulphuric acid concentrations. The relative contribution of estimated sulphuric acid to the growth rate was decreasing with increasing particle size and could explain more than 20% of the observed growth rate only for the 1.5–3 nm size range. The implication is that the sulphuric acid alone is not enough to explain the growth, but the highest growth rates seem to originate in VOC emissions following from biological activity. The frequency of new particle formation, however, increased nearly monotonously with the estimated sulphuric acid reaching 100% at H2SO4 concentration of 4×107cm−3, which suggests the formation and growth to be independent of each other.

Description: Nitrous acid (HONO) often plays an important role in tropospheric photochemistry as a major precursor of the hydroxyl radical (OH) in early morning hours and potentially during the day. However, the processes leading to formation of HONO and its vertical distribution at night, which can have a considerable impact on daytime ozone formation, are currently poorly characterized by observations and models. Long-path differential optical absorption spectroscopy (LP-DOAS) measurements of HONO during the 2006 TexAQS II Radical and Aerosol Measurement Project (TRAMP), near downtown Houston, TX, show nocturnal vertical profiles of HONO, with mixing ratios of up to 2.2 ppb near the surface and below 100 ppt aloft. Three nighttime periods of HONO, NO2 and O3 observations during TRAMP were used to perform model simulations of vertical mixing ratio profiles. By adjusting vertical mixing and NOx emissions the modeled NO2 and O3 mixing ratios showed very good agreement with the observations. Using a simple conversion of NO2 to HONO on the ground, direct HONO emissions, as well as HONO loss at the ground and on aerosol, the observed HONO profiles were reproduced well by the model. The unobserved increase of HONO to NO2 ratio (HONO/NO2) with altitude that was simulated by the initial model runs was found to be due to HONO uptake being too small on aerosol and too large on the ground. Refined model runs, with adjusted HONO uptake coefficients, showed much better agreement of HONO and HONO/NO2 for two typical nights, except during morning rush hour, when other HONO formation pathways are most likely active. One of the nights analyzed showed increase of HONO mixing ratios together with decreasing NO2 mixing ratios that the model was unable to reproduce, most likely due to the impact of weak precipitation during this night. HONO formation and removal rates averaged over the lowest 300 m of the atmosphere showed that NO2 to HONO conversion on the ground was the dominant source of HONO, followed by traffic emission. Aerosol did not play an important role in HONO formation. Although ground deposition was also a major removal pathway of HONO, net HONO production at the ground was the main source of HONO in our model studies. Sensitivity studies showed that in the stable NBL, net HONO production at the ground tends to increase with faster vertical mixing and stronger emission. Vertical transport was found to be the dominant source of HONO aloft.

Description: The quantification of sources of carbonaceous aerosol is important to understand their atmospheric concentrations and regulating processes and to study possible effects on climate and air quality, in addition to develop mitigation strategies. In the framework of the European Aerosol Cloud Climate Interaction (EUCAARI) project fine (Dp 〈 2.5 μm) and coarse (2.5 μm 〈 Dp 〈 10 μm) aerosol particles were sampled from February to June (wet season) and from August to September (dry season) 2008 in the Central Amazon Basin. The mass of fine particles averaged 2.4 μg m−3 during the wet season and 4.2 μg m−3 during the dry season. The average coarse aerosol mass concentration during wet and dry periods was 7.9 and 7.6 μg m−3, respectively. The overall chemical composition of fine and coarse mass did not show any seasonality with the largest fraction of fine and coarse aerosol mass explained by organic carbon (OC); the average OC to mass ratio was 0.4 and 0.6 in fine and coarse aerosol modes, respectively. The mass absorbing cross section of soot was determined by comparison of elemental carbon and light absorption coefficient measurements and it was equal to 4.7 m2 g−1 at 637 nm. Carbon aerosol sources were identified by Positive Matrix Factorization (PMF) analysis of thermograms: 43% of fine total carbon mass was assigned to biomass burning, 34% to secondary organic aerosol (SOA), and 23% to volatile species that are difficult to apportion. In the coarse mode, primary biogenic aerosol particles (PBAP) dominated the carbonaceous aerosol mass. The results confirmed the importance of PBAP in forested areas. The source apportionment results were employed to evaluate the ability of global chemistry transport models to simulate carbonaceous aerosol sources in a regional tropical background site. The comparison showed an overestimation of elemental carbon (EC) by the TM5 model during the dry season and OC both during the dry and wet periods. The overestimation was likely due to the overestimation of biomass burning emission inventories and SOA production over tropical areas.

Description: The frequency of occurrence of cirrus clouds and contrails, their life time, ice crystal size spectra and thus their radiative properties depend strongly on the ambient distribution of the relative humidity with respect to ice (RHice). Ice clouds do not form below a certain supersaturation and both cirrus and contrails need at least saturation conditions to persist over a longer period. Under subsaturated conditions, cirrus and contrails should dissipate. During the mid-latitude aircraft experiment CONCERT 2008 (CONtrail and Cirrus ExpeRimenT), RHice and ice crystals were measured in cirrus and contrails. Here, we present results from 2.3/1.7 h of observation in cirrus/contrails during 6 flights. Thin and subvisible cirrus with contrails embedded therein have been detected frequently in a subsaturated environment. Nevertheless, ice crystals up to radii of 50 μm and larger, but with low number densities were often observed inside the contrails as well as in the cirrus. Analysis of the meteorological situation indicates that the crystals in the contrails were entrained from the thin/subvisible cirrus clouds, which emerged in frontal systems with low updrafts. From model simulations of cirrus evaporation times it follows that such thin/subvisible cirrus can exist for time periods of a couple of hours and longer in a subsaturated environment and thus may represent a considerable part of the cirrus coverage.

Description: The atmospheric chemistry general circulation model ECHAM5/MESSy is used to simulate polar surface air temperature effects of geomagnetic activity variations. A transient model simulation was performed for the years 1960–2004 and is shown to develop polar surface air temperature patterns that depend on geomagnetic activity strength, similar to previous studies. In order to eliminate influencing factors such as sea surface temperatures (SST) or UV variations, two nine-year long simulations were carried out, with strong and weak geomagnetic activity, respectively, while all other boundary conditions were held to year 2000 levels. Statistically significant temperature effects that were observed in previous reanalysis and model results are also obtained from this set of simulations, suggesting that such patterns are indeed related to geomagnetic activity. In the model, strong geomagnetic activity and the associated NOx enhancements lead to polar stratospheric ozone loss. Compared with the simulation with weak geomagnetic activity, the ozone loss causes a decrease in ozone radiative cooling and thus a temperature increase in the polar winter mesosphere. Similar to previous studies, a cooling is found below the stratopause, which other authors have attributed to a decrease in the mean meridional circulation. In the polar stratosphere this leads to a more stable vortex. A strong (weak) Northern Hemisphere vortex is known to be associated with a positive (negative) Northern Annular Mode (NAM) index; our simulations exhibit a positive NAM index for strong geomagnetic activity, and a negative NAM for weak geomagnetic activity. Such NAM anomalies have been shown to propagate to the surface, and this is also seen in the model simulations. NAM anomalies are known to lead to specific surface temperature anomalies: a positive NAM is associated with warmer than average northern Eurasia and colder than average eastern North Atlantic. This is also the case in our simulation. Our simulations suggest a link between geomagnetic activity, ozone loss, stratospheric cooling, the NAM, and surface temperature variability.

Description: Sun-lit snow is increasingly recognized as a chemical reactor that plays an active role in uptake, transformation, and release of atmospheric trace gases. Snow is known to influence boundary layer air on a local scale, and given the large global surface coverage of snow may also be significant on regional and global scales. We present a new detailed one-dimensional snow chemistry module that has been coupled to the 1-D atmospheric boundary layer model MISTRA, we refer to the coupled model as MISTRA-SNOW. The new 1-D snow module, which is dynamically coupled to the overlaying atmospheric model, includes heat transport in the snowpack, molecular diffusion, and wind pumping of gases in the interstitial air. The model includes gas phase photochemistry and chemical reactions both in the interstitial air and the atmosphere. Heterogeneous and multiphase chemistry on atmospheric aerosol is considered explicitly. The chemical interaction of interstitial air with snow grains is simulated assuming chemistry in a liquid (aqueous) layer on the grain surface. The model was used to investigate snow as the source of nitrogen oxides (NOx) and gas phase reactive bromine in the atmospheric boundary layer in the remote snow covered Arctic (over the Greenland ice sheet) as well as to investigate the link between halogen cycling and ozone depletion that has been observed in interstitial air. The model is validated using data taken 10 June–13 June, 2008 as part of the Greenland Summit Halogen-HOx experiment (GSHOX). The model predicts that reactions involving bromide and nitrate impurities in the surface snow at Summit can sustain atmospheric NO and BrO mixing ratios measured at Summit during this period.

Description: This study reports laboratory measurements of cloud condensation nuclei (CCN) activity and droplet activation kinetics of aerosols dry-generated from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. Based on the observed dependence of critical supersaturation, sc, with particle dry diameter, Ddry, we find that FHH adsorption activation theory is a far more suitable framework for describing fresh dust CCN activity than Köhler theory. One set of FHH parameters (AFFH ~ 2.25 ± 0.75, BFFH ~ 1.20 ± 0.10) can adequately reproduce the measured CCN activity for all species considered, and also explains the large range of hygroscopicities reported in the literature. Based on threshold droplet growth analysis, mineral dust aerosols were found to display retarded activation kinetics compared to ammonium sulfate. Comprehensive simulations of mineral dust activation and growth in the CCN instrument suggest that this retardation is equivalent to a reduction of the water vapor uptake coefficient (relative to that for calibration ammonium sulfate aerosol) by 30–80%. These results suggest that dust particles do not require deliquescent material to act as CCN in the atmosphere.

Description: European pollutants are known to affect the Eastern Mediterranean (EM). However, there has been no previous study explicitly locating the European sources, characterizing their transport pathways, and quantifying their contribution to local concentrations in the EM. In the current study, spatially tagged carbon monoxide was used as a tracer for pollutant transport from Europe to the EM over five consecutive years (2003–2007) using the global chemical transport model MOZART-4. The model results were compared against NOAA/GMD ground station data and remotely sensed data from the Terra/MOPITT satellite and found to agree well. European anthropogenic emissions were found to significantly influence EM surface concentrations, while European biomass burning (BB) emissions were found to have only a small impact on EM surface concentrations. Over the five simulated years, only two European biomass burning episodes contributed more than 10 ppb to surface CO concentrations in the EM. CO enhancement in the EM during the summer was attributed to synoptic conditions prone to favorable transport from Turkey and Eastern Europe towards the EM rather than increased emissions. We attribute the apparently misleading association between CO emitted from European BB and CO enhancements over the EM to typical summer synoptic conditions caused by the lingering of an anticyclone positioned over the Western and Central Mediterranean Basin that lead to forest fires in the area. Combined with a barometric trough over the eastern part of the Mediterranean Basin, this generates a prevailing transport of air masses from Eastern Europe to the EM shore.

Description: Scattering and absorption were measured at the SMEAR II station in Hyytiälä, Finland, from October 2006 to May 2009. The average scattering coefficient σSP (λ=550 nm) 18 Mm−1 was about twice as much as at the Pallas GAW station in Finnish Lapland. The average absorption coefficient σAP (λ=550 nm) was 2.1 Mm−1. The seasonal cycles were analyzed from hourly-averaged data classified according to the measurement month. The ratio of the highest to the lowest average σSP and σAP was ~1.8 and ~2.8, respectively. The average single-scattering albedo (ω0) was 0.86 in winter and 0.91 in summer. σSP was highly correlated with the volume concentrations calculated from number size distributions in the size range 0.003–10 μm yielding PM10 mass scattering efficiency of 2.75 ± 0.01 g m−2 at λ=550 nm. Scattering coefficients were also calculated from the number size distributions by using a Mie code and the refractive index of ammonium sulfate. The linear regression yielded σSP(modelled)=1.04×σSP(measured) but there were also large deviations from the regression line: 10% of the σSP(modelled)-to-σSP(measured) ratios, calculated for each hour, were smaller than 0.9 and 10% of them were larger than 1.27. The scattering size distributions were bimodal, with a large submicrometer mode with geometric mean diameters Dg between ~300 and 400 nm and a smaller supermicrometer mode with Dg at ~1.5–1.9 μm. The contribution of submicrometer particles to scattering was ~90%. The Ångström exponent of scattering, αSP, was compared with the following weighted mean diameters: count mean diameter (CMD), surface mean diameter (SMD), scattering mean diameter (ScMD), condensation sink mean diameter (CsMD), and volume mean diameter (VMD). If αSP is to be used for estimating some measure of the size of particles, the best choice would be ScMD, then SMD, and then VMD. In all of these the qualitative relationship is similar: the larger the Ångström exponent, the smaller the weighted mean diameter. Contrary to these, CMD increased with increasing αSP and CsMD did not have any clear relationship with αSP. Source regions were estimated with backtrajectories and trajectory statistics. The geometric mean σSP and σAP associated with the grid cells in Eastern Europe were in the range 20–40 Mm−1 and 4–6 Mm−1, respectively. The respective geometric means of σSP and σAP in the grid cells over Norwegian Sea were in the range 5–10 Mm−1 and

Description: In the frame of the European project, entitled MULTI-ASSESS, specimens of structural metals, glass, stone and concrete materials were exposed to air pollution at a station, which was installed for this purpose on a building, located in the centre of Athens. The main purpose of this project was to determine the corrosion and soiling effects of air pollution on materials. A set of the specimens was exposed in a position that was sheltered from rain and partly from wind, and another set was exposed in unsheltered positions on the roof of the above said building. In addition, other specimens were exposed at different heights on the same building, in order to investigate for the first time the corrosion and soiling effects on various materials as a function of height. For the determination of these effects, chemical analysis of the specimens was performed and basic parameters as the weight change, the layer thickness and the optical properties were calculated. Finally, the results obtained are discussed and their plausible interpretation is attempted.

Description: The ash cloud of the Eyjafjallajökull1 volcano on Iceland caused closure of large parts of European airspace in April and May 2010. For the validation and improvement of the European volcanic ash forecast models several research flights were performed. Also the CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) flying laboratory, which routinely measures at cruise altitude (≈11 km) performed three dedicated measurements flights through sections of the ash plume. Although the focus of these flights was on the detection and quantification of the volcanic ash, we report here on sulphur dioxide (SO2) and bromine monoxide (BrO) measurements with the CARIBIC DOAS (Differential Optical Absorption Spectroscopy) instrument during the second of these special flights on 16 May 2010. As the BrO and the SO2 observations coincide, we assume the BrO to have been formed inside the volcanic plume. Both SO2 and BrO observations agree well with simultaneous satellite (GOME-2) observations. SO2 column densities retrieved from satellite observations are often used as an indicator for volcanic ash. For SO2 some additional information on the local distribution can be derived from a~comparison of forward and back scan GOME-2 data. More details on the local plume size and position are retrieved by combining CARIBIC and GOME-2 data. 1Also referred to as: Eyjafjalla (e.g. Schumann et al., 2010), Eyjafjöll or Eyjafjoll (e.g. Ansmann et al., 2010).

Description: This study explores the indirect effects of anthropogenic and biomass burning aerosols on Arctic clouds by co-locating a combination of MODIS and POLDER cloud products with output from the FLEXPART tracer transport model. During the activities of the International Polar Year for the Spring and Summer of 2008, we find a high sensitivity of Arctic cloud radiative properties to both anthropogenic and biomass burning pollution plumes, particularly at air temperatures near freezing or potential temperatures near 286 K. However, the sensitivity is much lower at both colder and warmer temperatures, likely due increases in the wet scavenging of cloud condensation nuclei: the pollution plumes remain but the component that influences clouds has been removed along transport pathways. The analysis shows that, independent of temperature, cloud optical depth is approximately four times more sensitive to changes in pollution levels than is cloud effective radius. This suggests that some form of feedback mechanism amplifies the radiative response of Arctic clouds to pollution through changes in cloud liquid water path.

Description: This paper presents an analysis of the recent tropospheric molecular hydrogen (H2) budget with a particular focus on soil uptake and surface emissions. A variational inversion scheme is combined with observations from the RAMCES and EUROHYDROS atmospheric networks, which include continuous measurements performed between mid-2006 and mid-2009. Net H2 surface flux, soil uptake distinct from surface emissions and finally, soil uptake, biomass burning, anthropogenic emissions and N2 fixation-related emissions separately were inverted in several scenarios. The various inversions generate an estimate for each term of the H2 budget. The net H2 flux per region (High Northern Hemisphere, Tropics and High Southern Hemisphere) varies between −8 and 8 Tg yr−1. The best inversion in terms of fit to the observations combines updated prior surface emissions and a soil deposition velocity map that is based on soil uptake measurements. Our estimate of global H2 soil uptake is −59 ± 4.0 Tg yr−1. Forty per cent of this uptake is located in the High Northern Hemisphere and 55% is located in the Tropics. In terms of surface emissions, seasonality is mainly driven by biomass burning emissions. The inferred European anthropogenic emissions are consistent with independent H2 emissions estimated using a H2/CO mass ratio of 0.034 and CO emissions considering their respective uncertainties. To constrain a more robust partition of H2 sources and sinks would need additional constraints, such as isotopic measurements.

Description: A major contribution to intensity changes of tropical cyclones (TCs) is believed to be associated with interaction with dry environmental air. However, the conditions under which pronounced TC-environment interaction takes place are not well understood. As a step towards improving our understanding of this problem we analyze the flow topology of a TC in vertical wind shear in an idealized, three-dimensional, convection-permitting numerical experiment. A set of distinct streamlines, the so-called separatrices, can be identified under the assumptions of steady and layer-wise horizontal flow. The separatrices are shown to divide the flow around the TC into distinct regions. The separatrix structure in our numerical experiment is more complex than the well-known flow topology of a non-divergent point vortex in uniform background flow. In particular, one separatrix spirals inwards and ends in a limit cycle, a meso-scale dividing streamline encompassing the eyewall above the inflow and below the outflow layer. Air with the highest values of moist entropy resides within this limit cycle supporting the notion that the eyewall is well protected from intrusion of dry environmental air despite the adverse impact of the vertical wind shear. This "moist envelope" is distorted considerably by the vertical wind shear, and the shape of the moist envelope is closely related to the shape of the limit cycle. A simple kinematic model based on a weakly divergent point vortex in background flow is presented. The model is shown to capture the essence of many salient features of the flow topology in the idealized experiment. A regime diagram representing realistic values of TC intensity and vertical wind shear can be constructed for this simple model. The results indicate distinct scenarios of environmental interaction depending on the ratio of storm intensity and shear magnitude. Further implications of the new results derived from the flow topology analysis for TCs in the real atmosphere are discussed.

Description: Three years (2006–2008) of ground-based observations of the Aerosol Optical Depth (AOD) in the urban environment of Athens, in the Eastern Mediterranean, are analysed in this work. Measurements were acquired with a Multi-Filter Rotating Shadowband Radiometer at five wavelengths. The daily average AOD at 500 nm is 0.23, and the mean Ångström coefficient calculated between 415 and 867 nm is 1.41. The annual variability of AOD has a spring maximum dominated by coarse dust particles from the Sahara (AOD 0.34–0.42), while the diurnal pattern is typical for urban sites, with AOD steadily increasing throughout the day. Secondary contributors of high aerosol loadings over Athens are identified, namely the Istanbul metropolitan area, the extended areas of biomass burning around the north coast of the Black Sea, power plants spread throughout the Balkans and the industrial area in the Po valley, with average daily AOD in the range of 0.25–0.35. The geographical distribution of the above sources in conjunction with the prevailing synoptic situation and contribution of local sources, lead to mixed types of aerosols over Athens with highly variable contribution of fine and coarse particles to AOD in the range 10%–90%. This is the first long-term, ground based data set available for Athens, and has also been used for the validation of satellite derived AOD by MODIS, showing good agreement on an annual basis, but with an overestimation of satellite AODs in the warm period.

Description: We have been conducting continuous measurements of CH4 and CO2 on a network of towers (JR-STATION: Japan–Russia Siberian Tall Tower Inland Observation Network) located in taiga, steppe, and wetland biomes of Siberia. Here we describe measurements from two forested bog sites, Karasevoe (KRS; 58°15′ N, 82°25′ E) and Demyanskoe (DEM; 59°47′ N, 70°52′ E), in West Siberia from 2005 to 2009. Although both CH4 and CO2 accumulation (ΔCH4 and ΔCO2) during nighttime (duration of 7 h beginning 21:30 LST) at KRS in July 2007 showed an anomalously high concentration, the higher ratios of ΔCH4/ΔCO2 compared with those in other years indicate that a considerably more CH4 flux occurred relative to the CO2 flux in response to large precipitation recorded in 2007 (~2.7 mm d−1 higher than the climatological 1979–1998 base). Estimated seasonal CH4 fluxes based on the ratio of ΔCH4/ΔCO2 and the CASA 3-hourly CO2 flux for the 2005–2009 period exhibited a seasonal variation with a maximum in July at both sites. Annual values of the CH4 emission from the forested bogs around KRS (approx. 7.8×104 km2) calculated from a process-based ecosystem model, Vegetation Integrative Simulator for Trace gases (VISIT), showed inter-annual variation of 0.54, 0.31, 0.94, 0.44, and 0.41 Tg CH4 yr−1 from 2005 to 2009, respectively, with the highest values in 2007. It was assumed in the model that the area flooded with water is proportional to the cumulative anomaly in monthly precipitation rate.

Description: We report simultaneous measurements of volatile organic compound (VOC) mixing ratios including C6 to C8 aromatics, isoprene, monoterpenes, acetone and organic aerosol mass loadings at a rural location in Southwestern Ontario, Canada by Proton-Transfer-Reaction Mass Spectrometry (PTR-MS) and Aerosol Mass Spectrometry (AMS), respectively. During the three-week-long Border Air Quality and Meteorology Study in June–July 2007, air was sampled from a range of sources, including aged air from the polluted US Midwest, direct outflow from Detroit 50 km away, and clean air with higher biogenic input. After normalization to the diurnal profile of CO, a long-lived tracer, diurnal analyses show clear photochemical loss of reactive aromatics and production of oxygenated VOCs and secondary organic aerosol (SOA) during the daytime. Biogenic VOC mixing ratios increase during the daytime in accord with their light- and temperature-dependent sources. Long-lived species, such as hydrocarbon-like organic aerosol and benzene show little to no photochemical reactivity on this timescale. From the normalized diurnal profiles of VOCs, an estimate of OH concentrations during the daytime, measured O3 concentrations, and laboratory SOA yields, we calculate integrated organic aerosol production amounts associated with each measured SOA precursor. Depending on whether the SOA formation is occurring in a low- or high-NOx regime, we estimate that the biogenic gases contribute between 10 to 36 times as much SOA as do the aromatic precursors, making this a highly biogenically dominated region for SOA formation. The conclusion that biogenic SOA formation is of significance to air quality in this region is supported by detailed air quality modeling during this period (Stroud et al., 2010).

Description: Simultaneous measurements of atomic iodine (I), molecular iodine (I2) and ultrafine particles were made at O Grove, Galicia (42.50° N, 8.87° W), on the northwest coast of Spain. The observations show a strong tidal signature, and indicate that the most probable sources of reactive iodine species are the exposed macroalgae during low tide. For the first time, I2 and I were concurrently measured revealing a high average I2/I ratio of ~32, which is higher than previously inferred by modelling studies. A 1-dimensional photochemical model is employed to simulate the observations showing that the high I2/I ratio can be reproduced in the presence of fast vertical mixing close to the surface, or using an extra chemical loss for I atoms with an unknown species. There is a lack of strong correlation between the I2/I and ultrafine particles, indicating that although they both have macroalgal sources, these were not at the same location. The model simulations also suggest that the source of the observed ultrafine particles is likely not very close to the measurement site, in order for the particles to form and grow, but the source for I and I2 must be local. Finally, the effect of NOx levels on iodine oxides, and the conditions under which iodine particle bursts will be suppressed, are explored.

Description: The record–breaking major stratospheric warming of northern winter 2009 (January–February) is studied using BASCOE (Belgian Assimilation System for Chemical ObsErvation) stratospheric water vapour analyses and MLS (Microwave Limb Sounder) water vapour observations, together with meteorological data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and potential vorticity derived from ECMWF meteorological data. We focus on the interaction between the cyclonic wintertime stratospheric polar vortex and subsidiary anticyclonic stratospheric circulations during the build-up, peak and aftermath of the major warming. We show dynamical consistency between the water vapour analysed fields, and the meteorological and PV fields. New results include the analysis of water vapour during the major warming and demonstration of the benefit of assimilating MLS satellite data into the BASCOE model.

Description: A quantum cascade laser based absorption spectrometer (QCLAS) is applied for the first time to perform in situ, continuous and high precision isotope ratio measurements of CO2 in the free troposphere. Time series of the three main CO2 isotopologue mixing ratios (12C16O2, 12C16O2 and 12C18O16O) have simultaneously been measured at one second time resolution over two years (from August 2008 to present) at the High Altitude Research Station Jungfraujoch (3580 m a.s.l., Switzerland). This work focuses on periods in February 2009 only, when sudden and pronounced enhancements in the tropospheric CO2 were observed. These short-term changes were closely correlated with variations in CO mixing ratios measured at the same site, indicating combustion related emissions as potential source. The analytical precision of 0.046‰ (at 50 s integration time) for both δ13C and δ18O and the high temporal resolution allowed the application of the Keeling plot method for source signature identification. The spatial origin of these CO2 emission sources was then determined by backward Lagrangian particle dispersion simulations.

Description: Businger and Delany (1990) presented an approach to estimate the sensor resolution required to limit the contribution of the uncertainty in the chemical concentration measurement to the flux measurement uncertainty to 10% for eddy covariance, gradient, and relaxed eddy accumulation flux measurement methods. We describe an improvement to their approach to estimate required resolution for the covariance method. In addition, we provide data to support selection of a form for the dimensionless scalar standard deviation similarity function based on observations of the variance of water vapor fluctuations from recent field experiments. We also redefine the atmospheric parameter of Businger and Delany in a more convenient, dimensionless form. To make the expression convenient for gas transfer applications, we introduce a "chemical parameter" based on the gas transfer (piston) velocity. Finally, we provide examples in which the approach is applied to measurement of carbon dioxide, dimethylsulfide, and hexachlorobenzene fluxes. The information provided here will be useful to plan field measurements of atmosphere-surface exchange fluxes of trace gases.

Description: Sea-salt aerosol mass, optical depth, and number concentration over the global oceans have significant implications for aerosol direct and indirect climate effects. We modeled sea-salt aerosol in a coupled climate and sectional microphysical model, CAM/CARMA, with aerosol dynamics including sea salt emission, gravitational sedimentation, dry deposition, wet scavenging, and particle swelling. We aimed at finding an integrated sea salt source function parameterization in the global climate model to simultaneously represent mass, optical depth, and number concentration. Each of these quantities is sensitive to a different part of the aerosol size distribution, which requires a size resolved microphysical model to treat properly. The CMS source function introduced in the research, based upon several earlier source functions, reproduced measurements of mass, optical depth and number concentration as well as the size distribution better than other source function choices we tried. However, as we note, it is also important to properly set the removal rate of the particles. The source function and removal rate are coupled in producing observed abundances. We find that sea-salt mass and optical depth peak in the winter, when winds are highest. However, surprisingly, particle numbers and CCN concentrations peak in summer when rainfall is lowest. The quadratic dependence of sea salt optical depth on wind speed, observed by some, is well represented in the model. We also found good agreement with the wind speed dependency of the number concentration at the measurement location and the regional scale. The work is the basis for further investigation of the effects of sea-salt aerosol on climate and atmospheric chemistry.

Description: This review is based on ca. 250 publications, from which 92 published data on the temporal and spatial variation of the concentration of small ions (

Description: Spaceborne lidar measurements from CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) are used to provide a vortex-wide perspective of the 2009–2010 Arctic polar stratospheric cloud (PSC) season to complement more focused measurements from the European Union RECONCILE (reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) field campaign. The 2009–2010 Arctic winter was unusually cold at stratospheric levels, especially from mid-December 2009 until the end of January 2010, and was one of only a few winters from the past 52 years with synoptic-scale regions of temperatures below the frost point. More PSCs were observed by CALIPSO during the 2009–2010 Arctic winter than in the previous three Arctic seasons combined. In particular, there were significantly more observations of high number density nitric acid trihydrate (NAT) mixtures (referred to as Mix 2-enh) and ice PSCs. We found that the 2009–2010 season could roughly be divided into four periods with distinctly different PSC optical characteristics. The early season (15–30 December 2009) was characterized by patchy, tenuous PSCs, primarily low number density liquid/NAT mixtures. The second phase of the season (31 December 2009–14 January 2010) was characterized by frequent mountain wave ice clouds that nucleated widespread NAT particles throughout the vortex, including Mix 2-enh. The third phase of the season (15–21 January 2010) was characterized by synoptic-scale temperatures below the frost point which led to a rare outbreak of widespread ice clouds. The fourth phase of the season (22–28 January) was characterized by a major stratospheric warming that distorted the vortex, displacing the cold pool from the vortex center. This final phase was dominated by supercooled ternary solution (STS) PSCs, although NAT particles may have been present in low number densities, but were masked by the more abundant STS droplets at colder temperatures. We also found distinct variations in the relative proportion of PSCs in each composition class with altitude over the course of the 2009–2010 Arctic season. Lower number density liquid/NAT mixtures were most frequently observed in the lower altitude regions of the clouds (below ∼18–20 km), which is consistent with CALIPSO observations in the Antarctic. Higher number density liquid/NAT mixtures, especially Mix 2-enh, were most frequently observed at altitudes above 18–20 km, primarily downstream of wave ice clouds. This pattern is consistent with the conceptual model whereby low number density, large NAT particles are precipitated from higher number density NAT clouds (i.e. mother clouds) that are nucleated downstream of mountain wave ice clouds.

Description: The UV Aerosol Indices (UVAI) form one of very few available tools in satellite remote sensing that provide information on aerosol absorption. The UVAI are also quite insensitive to surface type and are determined in the presence of clouds – situations where most aerosol retrieval algorithms do not work. The UVAI are most sensitive to elevated layers of absorbing aerosols, such as mineral dust and smoke from biomass burning, but they can also be used to study non-absorbing aerosols, such as sulphate and secondary organic aerosols. Although UVAI are determined for cloud-contaminated pixels, clouds do affect the value of UVAI in several ways. One way to correct for these effects is to remove clouded pixels using a cloud filter. However, this causes a large loss of data, biases the results towards clear skies, and removes all potentially very interesting pixels where aerosols and clouds co-exist. We here propose to correct the effects of clouds on UVAI in a more sophisticated way, namely by simulating the contribution of clouds to UVAI, and then subtracting it from the measured data. To this aim, we modelled UVAI from clouds by using measured cloud optical parameters – either with low spatial resolution from SCIAMACHY, or high resolution from MERIS – as input. The modelled UVAI were compared with UVAI measured by SCIAMACHY on different spatial (local, regional and global) and temporal scales (single measurement, daily means and seasonal means). The general dependencies of UVAI on cloud parameters were quite well reproduced, but several issues remain unclear: compared to the modelled UVAI, measured UVAI show a bias, in particular for large cloud fractions, and much larger scatter. Also, the viewing angle dependence differs for measured and modelled UVAI. The modelled UVAI from clouds will be used to correct measured UVAI for the effect of clouds, thus allowing a more quantitative analysis of UVAI and enabling investigations of aerosol-cloud interactions.

Description: Phase transitions of atmospheric water play a ubiquitous role in the Earth's climate system, but their direct impact on atmospheric dynamics has escaped wide attention. Here we examine and advance a theory as to how condensation influences atmospheric pressure through the mass removal of water from the gas phase with a simultaneous account of the latent heat release. Building from fundamental physical principles we show that condensation is associated with a decline in air pressure in the lower atmosphere. This decline occurs up to a certain height, which ranges from 3 to 4 km for surface temperatures from 10 to 30 °C. We then estimate the horizontal pressure differences associated with water vapor condensation and find that these are comparable in magnitude with the pressure differences driving observed circulation patterns. The water vapor delivered to the atmosphere via evaporation represents a store of potential energy available to accelerate air and thus drive winds. Our estimates suggest that the global mean power at which this potential energy is released by condensation is around one per cent of the global solar power – this is similar to the known stationary dissipative power of general atmospheric circulation. We conclude that condensation and evaporation merit attention as major, if previously overlooked, factors in driving atmospheric dynamics.

Description: Regional trans-boundary air pollution has become an important issue in the field of air pollution modeling. This paper presents the results of the implementation of the MM5-CMAQ modeling system in the Yangtze River Delta (YRD) for the months of January and July of 2004. The meteorological parameters are obtained by using the MM5 model. A new regional emission inventory with spatial and temporal allocations based on local statistical data has been developed to provide input emissions data to the MM5-CMAQ modeling system. The pollutant concentrations obtained from the MM5-CMAQ modeling system have been compared with observational data from the national air pollution monitoring network. It is found that air quality in winter in the YRD is generally worse than in summer, due mainly to unfavorable meteorological dispersion conditions. In winter the pollution transport from Northern China to the YRD reinforces the pollution caused by large local emissions. The monthly average concentration of SO2 in the YRD is 0.026 ± 0.011 mg m−3 in January and 0.017 ± 0.009 mg m−3 in July. Monthly average concentrations of NO2 in the YRD in January and July are 0.021 ± 0.009 mg m−3, and 0.014 ± 0.008 mg m−3 respectively. Visibility is also a problem, with average deciview values of 26.4 ± 2.95 dcv in winter and 17.6 ± 3.3 dcv in summer. The ozone concentration in the downtown area of a city like Zhoushan can be very high, with the highest simulated value reaching 107 ppb. Our results show that ozone and haze have become extremely important issues in the regional air quality. Thus, regional air pollution control is urgently needed to improve air quality in the YRD.

Description: Field experiments were performed to investigate the effects of photo-oxidation on fine particle emissions from an in-use CFM56-2B gas turbine engine mounted on a KC-135 Stratotanker airframe. Emissions were sampled into a portable smog chamber from a rake inlet installed one-meter downstream of the engine exit plane of a parked and chocked aircraft. The chamber was then exposed to sunlight and/or UV lights to initiate photo-oxidation. Separate tests were performed at different engine loads (4, 7, 30, 85%). Photo-oxidation created substantial secondary particulate matter (PM), greatly exceeding the direct PM emissions at each engine load after an hour or less of aging at typical summertime conditions. After several hours of photo-oxidation, the ratio of secondary-to-primary PM mass was on average 35 ± 4.1, 17 ± 2.5, 60 ± 2.2, and 2.7 ± 1.1 times the primary PM for the 4, 7, 30, and 85% load experiments, respectively. The composition of secondary PM formed strongly depended on load. At 4% load, secondary PM was dominated by secondary organic aerosol (SOA). At higher loads, the secondary PM was mainly secondary sulfate. Predictions of an SOA model are compared to the measured SOA formation. The SOA model predicts ~40% of the SOA produced during the 4% load experiment and ~60% for the 85% load experiment. Significant emissions of low-volatility compounds present in both the vapor- and particle-phase were measured in the exhaust and represent a significant pool of SOA precursors that appear to form SOA efficiently when oxidized. These results underscore the importance of accounting for atmospheric processing when assessing the influence of aircraft emissions on ambient PM levels.

Description: In this paper we present evidence that the observed increase in tropical upwelling after the year 2000 may be attributed to a change in the Brewer-Dobson circulation pattern. For this purpose, we use the concept of transit times derived from residual circulation trajectories and different in-situ measurements of ozone and nitrous dioxide. Observations from the Canadian midlatitude ozone profile record, probability density functions of in-situ N2O observations and a shift of the N2O-O3 correlation slopes, taken together, indicate that the increased upwelling in the tropics after the year 2000 appears to have triggered an intensification of tracer transport from the tropics into the extratropics in the lower stratosphere below about 500 K. This finding is corroborated by the fact that transit times along the shallow branch of the residual circulation into the LMS have decreased for the same time period (1993–2003). On a longer time scale (1979–2009), the transit time of the shallow residual circulation branch show a steady decrease of about −1 month/decade over the last 30 years, while the transit times of the deep branch remain unchanged. This highlights the fact that a change in the upwelling across the tropical tropopause is not a direct indicator for changes of the whole Brewer-Dobson circulation.

Description: Field observations and quantum chemical calculations have shown that organic amine compounds may be important in new particle formation processes involving H2SO4. Here, we report laboratory observations that investigate the effect of trimethylamine (TMA) on H2SO4-H2O nucleation made under aerosol precursor concentrations typically found in the lower troposphere ([H2SO4] of 106–107 cm−3; [TMA] of 180–1350 pptv). These results show that the threshold [H2SO4] needed to produce the unity nucleation rate ([H2SO4] of 106–107 cm−3) and the number of precursor molecules in the critical cluster (nH2SO4 = 4–6; nTMA = 1) are surprisingly similar to those found in the ammonia (NH3) ternary nucleation study (Benson et al., 2010a). At lower RH, however, enhancement in nucleation rates due to TMA was up to an order of magnitude greater than that due to NH3. These findings imply that both amines and NH3 are important nucleation species, but under dry atmospheric conditions, amines may have stronger effects on H2SO4 nucleation than NH3. Aerosol models should therefore take into account inorganic and organic bases together to fully understand the widespread new particle formation events in the lower troposphere.

Description: An ion chromatographic method is described for the quantification of the simple alkyl amines: methylamine (MA), dimethylamine (DMA), trimethylamine (TMA), ethylamine (EA), diethylamine (DEA) and triethylamine (TEA), in the ambient atmosphere. Limits of detection (3σ) are in the tens of pmol range for all of these amines, and good resolution is achieved for all compounds except for TMA and DEA. The technique was applied to the analysis of time-integrated samples collected using a micro-orifice uniform deposition impactor (MOUDI) with ten stages for size resolution of particles with aerodynamic diameters between 56 nm and 18 μm. In eight samples from urban and rural continental airmasses, the mass loading of amines consistently maximized on the stage corresponding to particles with aerodynamic diameters between 320 and 560 nm. The molar ratio of amines to ammonium (R3NH+/NH4+) in fine aerosol ranged between 0.005 and 0.2, and maximized for the smallest particle sizes. The size-dependence of the R3NH+/NH4+ ratio indicates differences in the relative importance of the processes leading to the incorporation of amines and ammonia into secondary particles. The technique was also used to make simultaneous hourly online measurements of amines in the gas phase and in fine particulate matter using an Ambient Ion Monitor Ion Chromatograph (AIM-IC). During a ten day campaign in downtown Toronto, DMA, TMA+DEA, and TEA were observed to range from below detection limit to 2.7 ppt in the gas phase. In the particle phase, MAH+ and TMAH++DEAH+ were observed to range from below detection limit up to 15 ng m−3. The presence of detectable levels of amines in the particle phase corresponded to periods with higher relative humidity and higher mass loadings of nitrate. While the hourly measurements made using the AIM-IC provide data that can be used the evaluate the application of gas-particle partitioning models to amines, the strong size-dependence of the R3NH+/NH4+ ratio indicates that using bulk measurements and an assumption of internal mixing may not be appropriate.

Description: The supply of bioavailable iron to the high-nitrate low-chlorophyll (HNLC) waters of the Southern Ocean through atmospheric pathways could stimulate phytoplankton blooms and have major implications for the global carbon cycle. In this study, model results and remotely-sensed data are analyzed to examine the horizontal and vertical transport pathways of Patagonian dust and quantify the effect of iron-laden mineral dust deposition on marine biological productivity in the surface waters of the South Atlantic Ocean (SAO). Model simulations for the atmospheric transport and deposition of mineral dust and bioavailable iron are carried out for two large dust outbreaks originated at the source regions of Northern Patagonia during the austral summer of 2009. Model-simulated horizontal and vertical transport pathways of Patagonian dust plumes are in reasonable agreement with remotely-sensed data. Simulations indicate that the synoptic meteorological patterns of high and low pressure systems are largely accountable for dust transport trajectories over the SAO. According to model results and retrievals from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), synoptic flows caused by opposing pressure systems (a high pressure system located to the east or north-east of a low pressure system) elevate the South American dust plumes well above the marine boundary layer. Under such conditions, the bulk concentration of mineral dust can quickly be transported around the low pressure system in a clockwise manner, follow the southeasterly advection pathway, and reach the HNLC waters of the SAO and Antarctica in ~3–4 days after emission from the source regions of Northern Patagonia. Two different mechanisms for dust-iron mobilization into a bioavailable form are considered in this study. A global 3-D chemical transport model (GEOS-Chem), implemented with an iron dissolution scheme, is employed to estimate the atmospheric fluxes of soluble iron, while a dust/biota assessment tool (Boyd et al., 2010) is applied to evaluate the amount of bioavailable iron formed through the slow and sustained leaching of dust in the ocean mixed layer. The effect of iron-laden mineral dust supply on surface ocean biomass is investigated by comparing predicted surface chlorophyll-a concentration ([Chl-a]) to remotely-sensed data. As the dust transport episodes examined here represent large summertime outflows of mineral dust from South American continental sources, this study suggests that (1) atmospheric fluxes of mineral dust from Patagonia are not likely to be the major source of bioavailable iron to ocean regions characterized by high primary productivity; (2) even if Patagonian dust plumes may not cause visible algae blooms, they could still influence background [Chl-a] in the South Atlantic sector of the Southern Ocean.

Description: The radiative forcing of dust and its impact on precipitation over the West Africa monsoon (WAM) region is simulated using a coupled meteorology and aerosol/chemistry model (WRF-Chem). During the monsoon season, dust is a dominant contributor to aerosol optical depth (AOD) over West Africa. In the control simulation, on 24-h domain average, dust has a cooling effect (−6.11 W/m2) at the surface, a warming effect (6.94 W/m2) in the atmosphere, and a relatively small TOA forcing (0.83 W/m2). Dust modifies the surface energy budget and atmospheric diabatic heating and hence causes lower atmospheric cooling in the daytime but warming in the nighttime. As a result, atmospheric stability is increased in the daytime and reduced in the nighttime, leading to a reduction of late afternoon precipitation by up to 0.14 mm/h (25%) and an increase of nocturnal and early morning precipitation by up to 0.04 mm/h (45%) over the WAM region. Dust-induced reduction of diurnal precipitation variation improves the simulated diurnal cycle of precipitation when compared to measurements. However, daily precipitation is only changed by a relatively small amount (−0.17 mm/day or −4%). The dust-induced change of WAM precipitation is not sensitive to interannual monsoon variability. On the other hand, sensitivity simulations show that, from weaker to stronger absorbing dust representing the uncertainty in dust solar absorptivity, dust longwave warming effect in the nighttime surpasses its shortwave cooling effect in the daytime at the surface, leading to a less stable atmosphere associated with more convective precipitation in the nighttime. As a result, the dust-induced change of daily WAM precipitation varies from a significant reduction of −0.52 mm/day (−12%, weaker absorbing dust) to a small increase of 0.03 mm/day (1%, stronger absorbing dust). This variation originates from the competition between dust impact on daytime and nighttime precipitation, which depends on dust shortwave absorption. Dust reduces the diurnal variation of precipitation regardless of its absorptivity, but more reduction is associated with stronger absorbing dust.

Description: Recent research has shown that orographic precipitation and the water resources that depend on it in the Colorado Rocky Mountains are sensitive to the variability of the region's aerosols, whether emitted locally or from distant sources. However, observations of cloud-active aerosols in western Colorado, climatologically upwind of the Colorado Rocky Mountains, have been limited to a few studies at a single, northern site. To address this knowledge gap, atmospheric aerosols were sampled at a ground site in southwestern Colorado and in low-level north to south transects of the Colorado Western Slope as part of the Inhibition of Snowfall by Pollution Aerosols (ISPA-III) field campaign. Total particle and cloud condensation nuclei (CCN) number concentration were measured for a 24-day period in Mesa Verde National Park, climatologically upwind of the San Juan Mountains, in Sept. and Oct. 2009. Regression analysis showed a positive relationship between mid-troposphere atmospheric pressure to the west of the site and the total particle count at the ground site, but no similar statistically significant relationship for the observed CCN. These data were supplemented with particle and CCN number concentration, as well as particle size distribution measurements aboard the KingAir platform during December 2009. A CCN closure attempt was performed using the size distribution information and suggested that the sampled aerosol in general had low hygroscopicity that changed slightly with the large-scale wind direction. Together, the sampled aerosols from these field programs were characteristic of a rural continental environment with a cloud active portion that varied slowly in time, and little in space along the Western Slope.

Description: During the African Monsoon Multidisciplinary Analyses (AMMA) airborne measurements of ozone, CO and nitrogen oxides by the French and German falcon aircraft took place near three cities in West Africa (Cotonou, Niamey and Ouagadougou). Significant ozone production (O3 increase of 40–50 ppbv) took place during two specific events: one near Cotonou on the coast of the Guinea Gulf, and the other near Niamey in the Sahel region. In both cases a high level of NOx (〉3 ppbv) is related to the ozone production. The ozone production is mainly driven by the Lagos-Cotonou anthropogenic emissions in Cotonou. In Niamey the combined effect of advection of VOC emissions from the forest and stagnation over the city area and the poorly vegetated soils recently wetted by convected systems is needed to achieve a similar level of ozone precursors. In Ouagadougou no ozone plume is found because of the absence of a pause in the convective activity and of the larger vegetated area around the city which prevented ozone plume formation during the wet season. To discuss the ozone increase near Cotonou two different approaches have been implemented: a FLEXPART simulation to quantify the probability of transport from the SH compared to air mass stagnation over the emission area and a simulation of the BOLAM mesoscale model with two different tracers for the anthropogenic emission (RETRO inventory for 2000) and the biomass burning. The BOLAM model shows a good agreement with the meteorological observations of the aircraft and allows to identify the key influence of the anthropogenic emissions in the first 3 km while the biomass burning plume remains above this altitude. The day to day variability of the ozone and CO in Niamey and Ouagadougou is discussed using FLEXPART simulations of the air mass stagnation in the 12° N–14° N latitude band and northward advection of air masses from the vegetated areas influenced by the biogenic volatile organic compound (VOC) emissions. Both conditions need to be fulfilled to be able to detect ozone increase within the city plume. The first condition is necessary to obtain a significant increase of the NOx concentrations by combining the city emission and the soil emission. It also shows that, contrary to the Niamey conditions, the Ouagadougou air mass transport and its timing respective to the convective activity did not correspond to favourable conditions for O3 formation during the time period of the aircraft data. Finally to check the magnitude of the ozone production related to the observed CO and NOx observations, a 2-days stationary run of the CittyCAT Lagrangian model was conducted at Cotonou location. The initialisation of the chemical concentrations not measured is done by scaling to the NOx and CO concentrations observed in the polluted plume. The scaling factor is derived from the low altitude observations provided by the DF20 and the BAe-146 aircraft during the AMMA campaign. Under such conditions, the simulation show that 50 ppbv of ozone can be produced in a 2-days period.

Description: Anthropogenic emissions of air pollutants in China influence not only local and regional environments but also the global atmospheric environment; therefore, it is important to understand how China's air pollutant emissions will change and how they will affect regional air quality in the future. Emission scenarios in 2020 were projected using forecasts of energy consumption and emission control strategies based on emissions in 2005, and on recent development plans for key industries in China. We developed four emission scenarios: REF[0] (current control legislations and implementation status), PC[0] (improvement of energy efficiencies and current environmental legislation), PC[1] (improvement of energy efficiencies and better implementation of environmental legislation), and PC[2] (improvement of energy efficiencies and strict environmental legislation). Under the REF[0] scenario, the emission of SO2, NOx, VOC and NH3 will increase by 17%, 50%, 49% and 18% in 2020, while PM will be reduced by 10% over East China, compared to that in 2005. In PC[2], sustainable energy polices will reduce SO2, NOx and PM10 emissions by 4.1 Tg, 2.6 Tg and 1.8 Tg, respectively; better implementation of current control policies will reduce SO2, NOx and PM10 emission by 2.9 Tg, 1.8 Tg, and 1.4 Tg, respectively; strict emission standards will reduce SO2, NOx and PM10 emissions by 3.2 Tg, 3.9 Tg, and 1.7 Tg, respectively. Under the PC[2] scenario, SO2 and PM10 emissions will decrease by 18% and 38%, while NOx and VOC emissions will increase by 3% and 8%, compared to that in 2005. Future air quality in China was simulated using the Community Multi-scale Air Quality Model (CMAQ) with 2005 emissions and 2020 emission scenarios. Under REF[0] emissions, the concentrations of SO2, NO2, hourly maximum ozone in summer, PM2.5, total sulfur and nitrogen depositions will increase by 5~47%, 45~53%, 8~12%, 4~15%, 4~37% and 7~14%, respectively, over East China. Under the PC[2] emission scenario, the concentrations of SO2, NO2, hourly maximal ozone in summer, PM2.5, total sulfur and nitrogen depositions will change by −28%~16%, −1%~11%, 1%~2%, −24%~−12%, −24%~13%, and 0~3%, respectively. The individual impacts of SO2, NOx, NH3, NMVOC and primary PM emission changes on ozone and PM2.5 concentrations have been analyzed using sensitivity analysis. The results suggest that NOx emission control need to be enhanced during the summertime to obtain both ozone and PM2.5 reduction benefits. NH3 emission controls should also be considered in order to reduce total nitrogen deposition in the future.

Description: Past research has shown that the dominant influence on recent global climate changes is from anthropogenic greenhouse gas increases with implications for future increases in global temperatures. One mitigation proposal is to reduce black carbon aerosol emissions. How much warming can be offset by the aerosol's control is unclear, especially as its influence on past climate has not been previously unambiguously detected. In this study observations of near-surface warming over the last century are compared with simulations using a climate model, HadGEM1. In the simulations black carbon, from fossil fuel and bio-fuel sources (fBC), produces a positive radiative forcing of about + 0.25 Wm−2 over the 20th century, compared with a little under + 2.5 Wm−2 for well mixed greenhouse gases. A simulated warming of global mean near-surface temperatures over the twentieth century from fBC of 0.14 ± 0.1 K compares with 1.06 ± 0.07 K from greenhouse gases, -0.58 ± 0.10 K from anthropogenic aerosols, ozone and land use changes and 0.09 ± 0.09 K from natural influences. Using a detection and attribution methodology, the observed warming since 1900 has detectable influences from anthropogenic and natural factors. Fossil fuel and bio-fuel black carbon is found to have a detectable contribution to the warming over the last 50 years of the 20th century, although the results are sensitive to a number of analysis choices, and fBC is not detected for the later fifty year period ending in 2006. The attributed warming of fBC was found to be consistent with the warming from the unscaled simulation. This study suggests that there is a possible significant influence from fBC on global temperatures, but its influence is small compared to that from greenhouse gas emissions.

Description: Hydroperoxy radical (HO2) concentrations were measured during the formal blind intercomparison campaign HOxComp carried out in Jülich, Germany. Three instruments detected HO2 via chemical conversion to hydroxyl radicals (OH) and subsequent detection of the sum of OH and HO2 by laser induced fluorescence (LIF). Instruments sampled ambient air for three days and were attached to the atmosphere simulation chamber SAPHIR during the second part of the campaign. Six experiments of one day each were conducted in SAPHIR, where air masses were homogeneously mixed, in order to investigate the performance of instruments and to determine potential interferences of measurements under well-controlled conditions. Linear correlation coefficients between measurements of the LIF instruments are generally high and range from 0.82 to 0.98. However, the agreement between measurements is variable. The regression analysis of the entire data set of measurements in SAPHIR yields slopes between 0.69 to 1.26 and intercepts are smaller than typical atmospheric daytime concentrations (less than 1 pptv). The quality of fit parameters improves significantly, when data are grouped into data subsets of similar water vapor concentrations. Because measurements of LIF instruments were corrected for a well-characterized water dependence of their sensitivities, this indicates that an unknown factor related to water vapor affected measurements in SAPHIR. Measurements in ambient air are also well correlated, but regression parameters differ from results obtained from SAPHIR experiments. This is most likely caused by sampling different air masses at the slightly distant locations of instruments.

Description: Secondary aerosol produced from marine biogenic sources in algal-rich coastal locations will initially be composed of iodine oxide species, most likely I2O5, or its hydrated form HIO3, formed as a result of iodine gas-phase chemistry. At present, there is no quantitative hygroscopic data for these compounds and very little data available for iodate solutions (HIO3 and I2O5 share a common aqueous phase). With increased interest in the role of such aerosol in the marine atmosphere, we have conducted studies of (i) the deliquescence behaviour of crystalline HIO3 and I2O5 at 273–303 K, (ii) the efflorescence behaviour of aqueous iodate solution droplets, and (iii) properties (water activity, density, and viscosity) of subsaturated and saturated iodate solutions. The deliquescence of I2O5 crystals at 293 K was observed to occur at a relative humidity (DRH) of 80.8±1.0%, whereas for HIO3, a DRH of 85.0±1.0% was measured. These values are consistent with measured water activity values for saturated I2O5 and HIO3 solutions at 293 K of 0.80±0.01 and 0.84±0.01 respectively. At all temperatures, DRH values for HIO3 crystals were observed to be higher than for those of I2O5. The temperature-dependent DRH data, along with solubility and water activity data were used to evaluate the enthalpy of solution (ΔHsol) for HIO3 and I2O5. A (ΔHsol value of 8.3±0.7 kJ mol−1 was determined for HIO3 which is consistent with a literature value of 8.8 kJ mol−1. For I2O5, we report for the first time its solubility at various temperatures and (ΔHsol=12.4±.6 kJ mol−1. The measured water activity values confirm that aqueous iodate solutions are strongly non-ideal, consistent with previous reports of complex ion formation and molecular aggregation.

Description: The impact of two recent gas-phase chemical kinetic mechanisms (CB05 and RACM2) on the formation of secondary inorganic and organic aerosols is compared for simulations of PM2.5 over Europe between 15 July and 15 August 2001. The host chemistry transport model is Polair3D of the Polyphemus air-quality platform. Particulate matter is modeled with SIREAM, which is coupled to the thermodynamic model ISORROPIA and to the secondary organic aerosol module MAEC. Model performance is satisfactory with both mechanisms for speciated PM2.5. The monthly-mean difference of the concentration of PM2.5 is less than 1 μg/m3 (6%) over the entire domain. Secondary chemical components of PM2.5 include sulfate, nitrate, ammonium and organic aerosols, and the chemical composition of PM2.5 is not significantly different between the two mechanisms. Monthly-mean concentrations of inorganic aerosol are higher with RACM2 than with CB05 (+16% for sulfate, +11% for nitrate, and +12% for ammonium), whereas the concentrations of organic aerosols are slightly higher with CB05 than with RACM2 (+26% for anthropogenic SOA and +1% for biogenic SOA). Differences in the inorganic and organic aerosols result primarily from differences in oxidant concentrations (OH, O3 and NO3). Nitrate formation tends to be HNO3-limited over land and differences in the concentrations of nitrate are due to differences in concentration of HNO3. Differences in aerosols formed from aromatics SVOC are due to different aromatics oxidation between CB05 and RACM2. The aromatics oxidation in CB05 leads to more cresol formation, which then leads to more SOA. Differences in the aromatics aerosols would be significantly reduced with the recent CB05-TU mechanism for toluene oxidation. Differences in the biogenic aerosols are due to different oxidant concentrations (monoterpenes) and different particulate organic mass concentrations affecting the gas-particle partitioning of SOA (isoprene).

Description: The tropical transport processes of 14 different models or model versions were compared, within the framework of the SCOUT-O3 (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) project. The tested models range from the regional to the global scale, and include numerical weather prediction (NWP), chemistry transport, and climate chemistry models. Idealised tracers were used in order to prevent the model's chemistry schemes from influencing the results substantially, so that the effects of modelled transport could be isolated. We find large differences in the vertical transport of very short lived tracers (with a lifetime of 6 hours) within the tropical troposphere. Peak convective outflow altitudes range from around 300 hPa to almost 100 hPa among the different models, and the upper tropospheric tracer mixing ratios differ by up to an order of magnitude. The timing of convective events is found to differ between the models, even among those which source their forcing data from the same NWP model (ECMWF). The differences are less pronounced for longer lived tracers, however they could have implications for the modelling of the halogen burden of the lowermost stratosphere through species such as bromoform, or for the transport of short lived hydrocarbons into the lowermost stratosphere. The modelled tracer profiles are found to be strongly influenced by the convective transport parameterisations, and boundary layer mixing parameterisations of the models. The location of rapid transport into the upper troposphere is similar among the models, and is mostly concentrated over the western Pacific, the Maritime Continent and the Indian Ocean. In contrast, none of the models indicates significant enhancement in upward transport over western Africa. The mean mixing ratios of an idealised CO like tracer in the upper tropical troposphere are found to be sensitive to the surface CO mixing ratios in the regions with the most active convection, revealing the importance of correctly modelling both the location of convective transport and the geographical pollutant emission patterns.

Description: The UK Met Office's Unified Model is used at a high global resolution (N216, ~0.83° × ~0.56°, ~60 km) to assess the impact of deep tropical convection on the structure of the tropical tropopause layer (TTL). We focus on the potential for rapid transport of short-lived ozone depleting species to the stratosphere by rapid convective uplift. The modelled horizontal structure of organised convection is shown to match closely with signatures found in the OLR satellite data. In the model, deep convective elevators rapidly lift air from 4–5 km up to 12–14 km. The influx of tropospheric air entering the TTL (11–12 km) is similar for all tropical regions with most convection stopping below ~14 km. The tropical tropopause is coldest and driest between November and February, coinciding with the greatest upwelling over the tropical warm pool. As this deep convection is co-located with bromine-rich biogenic coastal emissions, this period and location could potentially be the preferential gateway for stratospheric bromine.

Description: Regional and global chemical transport models underpredict NOx (NO+NO2) in the upper troposphere where it is a precursor to the greenhouse gas ozone. The NOx bias been shown in model evaluations using aircraft data (Singh et al., 2007) and total column NO2 (molecules cm−2) from satellite observations (Napelenok et al., 2008). The causes of NOx underpredictions have yet to be fully understood due to the interconnected nature of simulated emission, transport, and chemistry processes. Recent observation-based studies suggest that, in the upper troposphere, simulated chemistry overpredicts hydrogen radicals (OH• and HO2•) and would convert NOx to HNO3 too quickly (Olson et al., 2006; Bertram et al., 2007; Ren et al., 2008). Since typical chemistry evaluation techniques are not available for upper tropospheric conditions, this study develops an evaluation platform from in situ observations, stochastic convection, and deterministic chemistry. We derive a stochastic convection model and optimize it using two simulated datasets of time since convection, one based on meteorology and the other on chemistry. The chemistry surrogate for time since convection is calculated using seven different chemical mechanisms, all of which predict shorter time since convection than our meteorological analysis. We evaluate chemical simulations by inter-comparison and by pairing results with observations based on NOx:HNO3, a photochemical aging indicator. Inter-comparison reveals individual chemical mechanism biases and recommended updates. Evaluation against observations shows that all chemical mechanisms overpredict NOx removal relative to long-lived methanol and carbon monoxide. All chemical mechanisms underpredict observed NOx by at least 30%, and further evaluation is necessary to refine simulation sensitivities to initial conditions and chemical rate uncertainties.

Description: Mineral dust aerosols collected during the years 2008/2009 at the high-altitude research station Jungfraujoch (46°33´, 7°59´; 3580 m a.s.l.) were compared to windblown mineral dust deposited at the Colle Gnifetti glacier (45°55´ N, 7°52´ E; 4455 m a.s.l.) over the last millennium. Insoluble dust has been characterized in terms of mineralogy, Sr and Nd isotopic ratios, and trace element composition. Results demonstrate that the Saharan origin of the airborne dust did not change significantly throughout the past. Backward trajectories analysis of modern analogs furthermore confirms that major dust sources are situated in the north-central to north-western part of the Saharan desert. By contrast, less radiogenic Sr isotopic compositions are associated with lower abundances of crustal elements during low rates of dust deposition, suggesting intercontinental transport of background dust rather than activation of a secondary source. Saharan dust mobilization and meridional advection of air masses were relatively reduced during the second part of the Little Ice Age (ca. 1690–1870), except within the greatest Saharan dust event deposited around 1780–1790. Higher dust deposition with larger mean grain size and Saharan fingerprint began ca. 20 years after the industrial revolution of 1850, suggesting that increased mineral dust transport over the Alps during the last century was primarily due to drier winters in North Africa and stronger spring/summer North Atlantic southwesterlies, rather than to direct anthropogenic sources. Meanwhile, increasing carbonaceous particle emissions from fossil fuels combustion combined to higher lead enrichment factor during the last century, point to concomitant anthropogenic sources of particulate pollutants reaching high-altitude European glaciers.

Description: Vegetation commonly managed by prescribed burning was collected from five southeastern and southwestern US military bases and burned under controlled conditions at the US Forest Service Fire Sciences Laboratory in Missoula, Montana. The smoke emissions were measured with a large suite of state-of-the-art instrumentation including an open-path Fourier transform infrared (OP-FTIR) spectrometer for measurement of gas-phase species. The OP-FTIR detected and quantified 19 gas-phase species in these fires: CO2, CO, CH4, C2H2, C2H4, C3H6, HCHO, HCOOH, CH3OH, CH3COOH, furan, H2O, NO, NO2, HONO, NH3, HCN, HCl, and SO2. Emission factors for these species are presented for each vegetation type burned. Gas-phase nitrous acid (HONO), an important OH precursor, was detected in the smoke from all fires. The HONO emission factors ranged from 0.15 to 0.60 g kg−1 and were higher for the southeastern fuels. The fire-integrated molar emission ratios of HONO (relative to NOx) ranged from approximately 0.03 to 0.20, with higher values also observed for the southeastern fuels. The majority of non-methane organic compound (NMOC) emissions detected by OP-FTIR were oxygenated volatile organic compounds (OVOCs) with the total identified OVOC emissions constituting 61±12% of the total measured NMOC on a molar basis. These OVOC may undergo photolysis or further oxidation contributing to ozone formation. Elevated amounts of gas-phase HCl and SO2 were also detected during flaming combustion, with the amounts varying greatly depending on location and vegetation type. The fuels with the highest HCl emission factors were all located in the coastal regions, although HCl was also observed from fuels farther inland. Emission factors for HCl were generally higher for the southwestern fuels, particularly those found in the chaparral biome in the coastal regions of California.

Description: New burned area datasets and top-down constraints from atmospheric concentration measurements of pyrogenic gases have decreased the large uncertainty in fire emissions estimates. However, significant gaps remain in our understanding of the contribution of deforestation, savanna, forest, agricultural waste, and peat fires to total global fire emissions. Here we used a revised version of the Carnegie-Ames-Stanford-Approach (CASA) biogeochemical model and improved satellite-derived estimates of area burned, fire activity, and plant productivity to calculate fire emissions for the 1997–2009 period on a 0.5° spatial resolution with a monthly time step. For November 2000 onwards, estimates were based on burned area, active fire detections, and plant productivity from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. For the partitioning we focused on the MODIS era. We used burned area estimates based on Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS) and Along-Track Scanning Radiometer (ATSR) active fire data prior to MODIS (1997–2000) and Advanced Very High Resolution Radiometer (AVHRR) derived estimates of plant productivity during the same period. Average global fire carbon emissions were 2.0 Pg yr−1 with significant interannual variability during 1997–2001 (2.8 Pg yr−1 in 1998 and 1.6 Pg yr−1 in 2001). Emissions during 2002–2007 were relatively constant (around 2.1 Pg yr−1) before declining in 2008 (1.7 Pg yr−1) and 2009 (1.5 Pg yr−1) partly due to lower deforestation fire emissions in South America and tropical Asia. During 2002–2007, emissions were highly variable from year-to-year in many regions, including in boreal Asia, South America, and Indonesia, but these regional differences cancelled out at a global level. During the MODIS era (2001–2009), most fire carbon emissions were from fires in grasslands and savannas (44%) with smaller contributions from tropical deforestation and degradation fires (20%), woodland fires (mostly confined to the tropics, 16%), forest fires (mostly in the extratropics, 15%), agricultural waste burning (3%), and tropical peat fires (3%). The contribution from agricultural waste fires was likely a lower bound because our approach for measuring burned area could not detect all of these relatively small fires. For reduced trace gases such as CO and CH4, deforestation, degradation, and peat fires were more important contributors because of higher emissions of reduced trace gases per unit carbon combusted compared to savanna fires. Carbon emissions from tropical deforestation, degradation, and peatland fires were on average 0.5 Pg C yr−1. The carbon emissions from these fires may not be balanced by regrowth following fire. Our results provide the first global assessment of the contribution of different sources to total global fire emissions for the past decade, and supply the community with an improved 13-year fire emissions time series.

Description: Emissions of CO2 from fossil fuel combustion are a critical quantity that must be accurately given in established flux inversion frameworks. Work with emerging satellite-based inversions requires spatiotemporally-detailed inventories that permit analysis of regional sources and sinks. Conventional approaches for disaggregating national emissions beyond the country and city levels based on population distribution have certain difficulties in their application. We developed a global 1 km×1 km fossil fuel CO2 emission inventory for the years 1980–2007 by combining a worldwide point source database and satellite observations of the global nightlight distribution. In addition to estimating the national emissions using global energy consumption statistics, emissions from point sources were estimated separately and were spatially allocated to exact locations indicated by the point source database. Emissions from other sources were distributed using a special nightlight dataset that had fewer saturated pixels compared with regular nightlight datasets. The resulting spatial distributions differed in several ways from those derived using conventional population-based approaches. Because of the inherent characteristics of the nightlight distribution, source regions corresponding to human settlements and land transportation were well articulated. Our distributions showed good agreement with a high-resolution inventory across the US at spatial resolutions that were adequate for regional flux inversions. The inventory will be incorporated into models for operational flux inversions that use observational data from the Japanese Greenhouse Gases Observing SATellite (GOSAT).

Description: Understanding the processes controlling black carbon (BC) in the Arctic is crucial for evaluating the impact of anthropogenic and natural sources of BC on Arctic climate. Vertical profiles of BC mass were observed from the surface to near 7-km altitude in April 2008 using a Single-Particle Soot Photometer (SP2) during flights on the NOAA WP-3D research aircraft from Fairbanks, Alaska. These measurements were conducted during the NOAA-sponsored Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) project as part of POLARCAT, an International Polar Year (IPY) activity. In the free troposphere, the Arctic air mass was influenced by long-range transport from biomass-burning and anthropogenic source regions at lower latitudes especially during the latter part of the campaign. Maximum average BC mass loadings of 150 ng kg−1 were observed near 5.5-km altitude in the aged Arctic air mass. In biomass-burning plumes, BC was enhanced from near the top of the Arctic boundary layer (ABL) to 5.5 km compared to the aged Arctic air mass. At the bottom of some of the profiles, positive vertical gradients in BC were observed in the vicinity of open leads in the sea-ice. BC mass loadings increased by about a factor of two across the boundary layer transition in the ABL in these cases while carbon monoxide (CO) remained constant, evidence for depletion of BC in the ABL. BC mass loadings were positively correlated with O3 in ozone depletion events (ODEs) for all the observations in the ABL suggesting that BC was removed by dry deposition of BC on the snow or ice because molecular bromine, Br2, which photolyzes and catalytically destroys O3, is thought to be released near the open leads in regions of ice formation. We estimate the deposition flux of BC mass to the snow using a box model constrained by the vertical profiles of BC in the ABL. The open leads may increase vertical mixing in the ABL and entrainment of pollution from the free troposphere possibly enhancing the deposition of BC to the snow.

Description: Measurements of nitrous acid (HONO) were performed as part of the 2007 Border Air Quality and Meteorology Study (BAQS-Met) at the Harrow Ontario supersite between 20 June and 10 July 2007. Nitrous acid is an important precursor of the hydroxy radical and understanding its chemistry is important to understanding daytime oxidation chemistry. The HONO measurements were made using a custom built Long Path Absorption Photometer (LOPAP). The goal of this work was to shed light on sources of daytime HONO in the border region. During the course of the campaign HONO mixing ratios consistently exceeded expected daytime values by as much as a factor of 6. Mean daytime concentrations of 61 pptv were observed. While HONO decay began at sunrise, minimum HONO values were not measured until the late afternoon. There was little difference between the daytime (mean=1.5%) and night-time (mean=1.7%) ratios of HONO/NO2. Thus there was a very strong daytime source of HONO which is consistent with other recent studies. Correlations of daytime HONO production with a variety of chemical and meteorological parameters indicate that production is dependent on UV radiation, NO2 and water vapour but is not consistent with a simple gas phase process. Apparent rate constants for the production of HONO from photolyticly excited NO2 and water vapour vary from 2.8–7.8×10−3 molec−1 s−1, during the campaign.