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  • 1
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    Stratospheric sulfur and its implications for radiative forcing simulated by the chemistry climate model EMAC (2015)
    Wiley
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    Publication Date: 2015-02-10
    Description: Multiyear simulations with the atmospheric chemistry general circulation model EMAC with a microphysical modal aerosol module at high vertical resolution demonstrate that the sulfur gases COS and SO 2 , the latter from low-latitude and midlatitude volcanic eruptions, predominantly control the formation of stratospheric aerosol. Marine dimethyl sulfide (DMS) and other SO 2 sources, including strong anthropogenic emissions in China, are found to play a minor role except in the lowermost stratosphere. Estimates of volcanic SO 2 emissions are based on satellite observations using TOMS and OMI for total injected mass and MIPAS on ENVISAT or SAGE for the spatial distribution. The 10 year SO 2 and COS dataset of MIPAS is also used for model evaluation. The calculated radiative forcing of stratospheric background aerosol including sulfate from COS and small contributions by DMS oxidation, and organic aerosol from biomass burning, is about 0.07 W/m 2 . For stratospheric sulfate aerosol from medium and small volcanic eruptions between 2005 and 2011 a global radiative forcing up to 0.2 W/m 2 is calculated, moderating climate warming, while for the major Pinatubo eruption the simulated forcing reaches 5 W/m 2 , leading to temporary climate cooling. The Pinatubo simulation demonstrates the importance of radiative feedback on dynamics, e.g., enhanced tropical upwelling, for large volcanic eruptions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Distribution of methane in the tropical upper troposphere measured by CARIBIC and CONTRAIL aircraft (2012)
    Wiley
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    Publication Date: 2012-10-04
    Description: We investigate the upper tropospheric distribution of methane (CH4) at low latitudes based on the analysis of air samples collected from aboard passenger aircraft. The distribution of CH4 exhibits spatial and seasonal differences, such as the pronounced seasonal cycles over tropical Asia and elevated mixing ratios over central Africa. Over Africa, the correlations of methane, ethane, and acetylene with carbon monoxide indicate that these high mixing ratios originate from biomass burning as well as from biogenic sources. Upper tropospheric mixing ratios of CH4 were modeled using a chemistry transport model. The simulation captures the large-scale features of the distributions along different flight routes, but discrepancies occur in some regions. Over Africa, where emissions are not well constrained, the model predicts a too steep interhemispheric gradient. During summer, efficient convective vertical transport and enhanced emissions give rise to a large-scale CH4 maximum in the upper troposphere over subtropical Asia. This seasonal (monsoonal) cycle is analyzed with a tagged tracer simulation. The model confirms that in this region convection links upper tropospheric mixing ratios to regional sources on the Indian subcontinent, subtropical East Asia, and Southeast Asia. This type of aircraft data can therefore provide information about surface fluxes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Intercomparison of temperature and precipitation data sets based on observations in the Mediterranean and the Middle East (2012)
    Wiley
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    Publication Date: 2012-06-20
    Description: This paper presents an intercomparison and evaluation of gridded temperature and precipitation data sets, based on observations in the Mediterranean and the Middle East region. Using available global and regional data, we investigate the spatial and seasonal distributions of these two parameters, including uncertainties and trends for eight subregions that signify distinct climate regimes. All data sets represent the overall spatial features well though partly with biases. Using the seasonal means, standard deviations and cumulative density functions for the eight subregions, we identify outliers among the data sets. The correlations between data sets are high except for some regional data products. Desert areas such as Saudi Arabia and Libya-Egypt appear problematic due to their sparse station network. Similar upward trends of temperature and downward trends in precipitation are found for most of the region in all data sets, while differences appear in their magnitude and level of significance.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Quantifying the transport of sub-cloud layer reactants by shallow cumulus clouds over the Amazon (2013)
    Wiley
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    Publication Date: 2013-10-22
    Description: [1]  We investigate the vertical transport of atmospheric chemical reactants from the sub-cloud layer to the cumulus cloud layer driven by shallow convection over the Amazon during the dry season. The dynamical and chemical assumptions needed for mesoscale and global chemistry-transport model parametrizations are systematically analysed using a Large-Eddy Simulation model. We quantify the mass-flux transport contribution to the temporal evolution of reactants. Isoprene, a key atmospheric compound over the tropical rain forest, decreases by 8.5 % hr − 1 on average and 15 % hr − 1 at maximum due to mass-flux induced removal. We apply mass-flux parametrizations for the transport of chemical reactants and obtain satisfactory agreement with numerically resolved transport, except for some reactants like O 3 , NO and NO 2 . The latter is caused by the local partitioning of reactants, influenced by UV radiation extinction by clouds and small-scale variability of ambient atmospheric compounds. By considering the longer lived NO x (NO + NO 2 ), the transport is well represented by the parametrization. Finally, by considering heterogeneous surface exchange conditions, it is demonstrated that the parametrizations are sensitive to boundary conditions due to changes in the boundary-layer dynamics.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    HOx budgets during HOxComp: A case study of HOx chemistry under NOx-limited conditions (2012)
    Wiley
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    Publication Date: 2012-02-10
    Description: Recent studies have shown that measured OH under NOx-limited, high-isoprene conditions are many times higher than modeled OH. In this study, a detailed analysis of the HOx radical budgets under low-NOx, rural conditions was performed employing a box model based on the Master Chemical Mechanism (MCMv3.2). The model results were compared with HOx radical measurements performed during the international HOxComp campaign carried out in Jülich, Germany, during summer 2005. Two different air masses influenced the measurement site denoted as high-NOx (NO, 1–3 ppbv) and low-NOx (NO, 〈 1 ppbv) periods. Both modeled OH and HO2 diurnal profiles lay within the measurement range of all HOx measurement techniques, with correlation slopes between measured and modeled OH and HO2 around unity. Recently discovered interference in HO2 measurements caused by RO2 cross sensitivity was found to cause a 30% increase in measured HO2 during daytime on average. After correction of the measured HO2 data, the model HO2 is still in good agreement with the observations at high NOx but overpredicts HO2 by a factor of 1.3 to 1.8 at low NOx. In addition, for two different set of measurements, a missing OH source of 3.6 ± 1.6 and 4.9 ± 2.2 ppb h−1 was estimated from the experimental OH budget during the low-NOx period using the corrected HO2 data. The measured diurnal profile of the HO2/OH ratio, calculated using the corrected HO2, is well reproduced by the MCM at high NOx but is significantly overestimated at low NOx. Thus, the cycling between OH and HO2 is better described by the model at high NOx than at low NOx. Therefore, similar comprehensive field measurements accompanied by model studies are urgently needed to investigate HOx recycling under low-NOx conditions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Atmospheric oxidation capacity sustained by a tropical forest (2008)
    Nature Publishing Group (NPG)
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    Publication Date: 2008-04-11
    Description: Terrestrial vegetation, especially tropical rain forest, releases vast quantities of volatile organic compounds (VOCs) to the atmosphere, which are removed by oxidation reactions and deposition of reaction products. The oxidation is mainly initiated by hydroxyl radicals (OH), primarily formed through the photodissociation of ozone. Previously it was thought that, in unpolluted air, biogenic VOCs deplete OH and reduce the atmospheric oxidation capacity. Conversely, in polluted air VOC oxidation leads to noxious oxidant build-up by the catalytic action of nitrogen oxides (NO(x) = NO + NO2). Here we report aircraft measurements of atmospheric trace gases performed over the pristine Amazon forest. Our data reveal unexpectedly high OH concentrations. We propose that natural VOC oxidation, notably of isoprene, recycles OH efficiently in low-NO(x) air through reactions of organic peroxy radicals. Computations with an atmospheric chemistry model and the results of laboratory experiments suggest that an OH recycling efficiency of 40-80 per cent in isoprene oxidation may be able to explain the high OH levels we observed in the field. Although further laboratory studies are necessary to explore the chemical mechanism responsible for OH recycling in more detail, our results demonstrate that the biosphere maintains a remarkable balance with the atmospheric environment.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lelieveld, J -- Butler, T M -- Crowley, J N -- Dillon, T J -- Fischer, H -- Ganzeveld, L -- Harder, H -- Lawrence, M G -- Martinez, M -- Taraborrelli, D -- Williams, J -- England -- Nature. 2008 Apr 10;452(7188):737-40. doi: 10.1038/nature06870.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Chemistry, 27 Becherweg, 55128 Mainz, Germany. lelieveld@mpch-mainz.mpg.de〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18401407" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Atlantic Ocean ; Atmosphere/*chemistry ; Butadienes/metabolism ; French Guiana ; Guyana ; Hemiterpenes/metabolism ; Hydroxyl Radical/metabolism ; Nitric Oxide/metabolism ; Oxidation-Reduction ; Ozone/analysis ; Pentanes/metabolism ; Suriname ; Trees/*metabolism ; *Tropical Climate
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 7
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    Atmospheric chemistry: A missing sink for radicals (2010)
    Nature Publishing Group (NPG)
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    Publication Date: 2010-08-21
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lelieveld, Jos -- England -- Nature. 2010 Aug 19;466(7309):925-6. doi: 10.1038/466925a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/20725025" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 8
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    Dynamics of Tropical-Extratropical Interactions and Extreme Precipitation Events in Saudi Arabia in Autumn, Winter and Spring (2016)
    Wiley
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    Publication Date: 2016-03-03
    Description: Extreme precipitation in the arid Middle East can cause flash floods with dramatic societal impacts. This study investigates the synoptic-scale dynamics of three extreme precipitation events that occurred in Saudi Arabia in autumn, winter and spring. Using ERA-Interim reanalysis, sounding, and observational precipitation data, we study precipitation characteristics, the synoptic circulations, moisture transport pathways and forcing mechanisms for upward motion. All three cases involved strong tropical-extratropical interactions whereby midlatitude forcing instigated an incursion of tropical moisture over the Arabian Peninsula that fueled the heavy rainfall. In each case, a midlatitude upper-level trough, associated with anticyclonic Rossby wave breaking, intruded into the subtropics. The phase relationship between this trough and the tropical low-level circulation was consistent with wave amplification through baroclinic growth. Eulerian and Lagrangian analyses reveal moisture transport from nearby and remote tropical regions, leading to above-normal tropospheric moisture content over Saudi Arabia. The autumn case (November 2009) showed a transient midlatitude upper-level trough that interacted with the climatological Red Sea Trough near the surface, being an “Active Red Sea Trough” event. The winter case (January 2005) resembled tropical plume-like characteristics and demonstrated the coupling of a midlatitude cyclone and the equatorial low-pressure zone over Africa, an intensified subtropical jet stream, and pronounced moisture fluxes at middle and upper levels. The spring case (April-May 2013) involved a quasi-stationary cutoff low and persistent advection of low-level moist air masses, partly from the South Indian Ocean through cross-equatorial flow. The forcing of ascent was associated with low-level moisture convergence and decreased static stability (autumn case), dynamical lifting (winter case), strong surface sensible heating (spring case), and orographic lifting (all cases), favouring the buildup and release of potential instability. We discuss the three cases from a seasonal perspective and present a synthesis of their common key synoptic features.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 9
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    The contribution of outdoor air pollution sources to premature mortality on a global scale (2015)
    Nature Publishing Group (NPG)
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    Publication Date: 2015-09-19
    Description: Assessment of the global burden of disease is based on epidemiological cohort studies that connect premature mortality to a wide range of causes, including the long-term health impacts of ozone and fine particulate matter with a diameter smaller than 2.5 micrometres (PM2.5). It has proved difficult to quantify premature mortality related to air pollution, notably in regions where air quality is not monitored, and also because the toxicity of particles from various sources may vary. Here we use a global atmospheric chemistry model to investigate the link between premature mortality and seven emission source categories in urban and rural environments. In accord with the global burden of disease for 2010 (ref. 5), we calculate that outdoor air pollution, mostly by PM2.5, leads to 3.3 (95 per cent confidence interval 1.61-4.81) million premature deaths per year worldwide, predominantly in Asia. We primarily assume that all particles are equally toxic, but also include a sensitivity study that accounts for differential toxicity. We find that emissions from residential energy use such as heating and cooking, prevalent in India and China, have the largest impact on premature mortality globally, being even more dominant if carbonaceous particles are assumed to be most toxic. Whereas in much of the USA and in a few other countries emissions from traffic and power generation are important, in eastern USA, Europe, Russia and East Asia agricultural emissions make the largest relative contribution to PM2.5, with the estimate of overall health impact depending on assumptions regarding particle toxicity. Model projections based on a business-as-usual emission scenario indicate that the contribution of outdoor air pollution to premature mortality could double by 2050.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lelieveld, J -- Evans, J S -- Fnais, M -- Giannadaki, D -- Pozzer, A -- England -- Nature. 2015 Sep 17;525(7569):367-71. doi: 10.1038/nature15371.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Max Planck Institute for Chemistry, Atmospheric Chemistry Department, 55128 Mainz, Germany. ; The Cyprus Institute, Energy, Environment and Water Research Center, 1645 Nicosia, Cyprus. ; Harvard School of Public Health, Boston, Massachusetts 02215, USA. ; Cyprus International Institute for Environment and Public Health, Cyprus University of Technology, 3041 Limassol, Cyprus. ; King Saud University, College of Science, Riyadh 11451, Saudi Arabia.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26381985" target="_blank"〉PubMed〈/a〉
    Keywords: Adult ; Agriculture/statistics & numerical data ; Air Pollutants/*adverse effects/poisoning ; Air Pollution/*adverse effects ; Atmosphere/chemistry ; Biomass ; Child, Preschool ; China/epidemiology ; Cooking/statistics & numerical data ; Environmental Exposure/*adverse effects ; Environmental Monitoring ; Europe/epidemiology ; Far East/epidemiology ; Fires/statistics & numerical data ; Heating/statistics & numerical data ; Humans ; India/epidemiology ; Infant ; *Internationality ; Middle Aged ; *Mortality, Premature/trends ; Ozone/adverse effects/analysis/poisoning ; Particulate Matter/*adverse effects/poisoning ; Power Plants/statistics & numerical data ; Rural Health/statistics & numerical data ; Russia/epidemiology ; United States/epidemiology ; Urban Health/statistics & numerical data ; Vehicle Emissions/poisoning
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 10
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    Significant concentrations of nitryl chloride observed in rural continental Europe associated with the influence of sea salt chloride and anthropogenic emissions (2012)
    Wiley
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    Publication Date: 2012-05-26
    Description: We present the first measurements of nitryl chloride (ClNO2) over continental Europe. Significant quantities of ClNO2, up to 800 pptv, were measured at a mountaintop field site in Hessen, southwest Germany. ClNO2 was detected during the majority of nights between the 15th August and 16th September 2011, its largest mixing ratios being associated with air masses influenced by sea salt and anthropogenic NOx emissions. ClNO2 persisted in measurable quantities until early afternoons on days with low photolysis frequencies. As a consequence, early morning production rates of Cl atoms could significantly exceed the production of OH via ozone photolysis, likely leading to increased O3 production.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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