ALBERT

Description: A multi-model intercomparison of halogenated very short-lived substances (TransCom-VSLS): linking oceanic emissions and tropospheric transport for a reconciled estimate of the stratospheric source gas injection of bromine R. Hossaini, P. K. Patra, A. A. Leeson, G. Krysztofiak, N. L. Abraham, S. J. Andrews, A. T. Archibald, J. Aschmann, E. L. Atlas, D. A. Belikov, H. Bönisch, L. J. Carpenter, S. Dhomse, M. Dorf, A. Engel, W. Feng, S. Fuhlbrügge, P. T. Griffiths, N. R. P. Harris, R. Hommel, T. Keber, K. Krüger, S. T. Lennartz, S. Maksyutov, H. Mantle, G. P. Mills, B. Miller, S. A. Montzka, F. Moore, M. A. Navarro, D. E. Oram, K. Pfeilsticker, J. A. Pyle, B. Quack, A. D. Robinson, E. Saikawa, A. Saiz-Lopez, S. Sala, B.-M. Sinnhuber, S. Taguchi, S. Tegtmeier, R. T. Lidster, C. Wilson, and F. Ziska Atmos. Chem. Phys., 16, 9163-9187, doi:10.3334/CDIAC/hippo_012, 2016 The first concerted multi-model intercomparison of halogenated very short-lived substances (VSLS) has been performed, within the framework of the ongoing Atmospheric Tracer Transport Model Intercomparison Project (TransCom). Eleven global models or model variants participated (nine chemical transport models and two chemistry–climate models) by simulating the major natural bromine VSLS, bromoform (CHBr 3 ) and dibromomethane (CH 2 Br 2 ), over a 20-year period (1993–2012). Except for three model simulations, all others were driven offline by (or nudged to) reanalysed meteorology. The overarching goal of TransCom-VSLS was to provide a reconciled model estimate of the stratospheric source gas injection (SGI) of bromine from these gases, to constrain the current measurement-derived range, and to investigate inter-model differences due to emissions and transport processes. Models ran with standardised idealised chemistry, to isolate differences due to transport, and we investigated the sensitivity of results to a range of VSLS emission inventories. Models were tested in their ability to reproduce the observed seasonal and spatial distribution of VSLS at the surface, using measurements from NOAA's long-term global monitoring network, and in the tropical troposphere, using recent aircraft measurements – including high-altitude observations from the NASA Global Hawk platform. The models generally capture the observed seasonal cycle of surface CHBr 3 and CH 2 Br 2 well, with a strong model–measurement correlation ( r   ≥  0.7) at most sites. In a given model, the absolute model–measurement agreement at the surface is highly sensitive to the choice of emissions. Large inter-model differences are apparent when using the same emission inventory, highlighting the challenges faced in evaluating such inventories at the global scale. Across the ensemble, most consistency is found within the tropics where most of the models (8 out of 11) achieve best agreement to surface CHBr 3 observations using the lowest of the three CHBr 3 emission inventories tested (similarly, 8 out of 11 models for CH 2 Br 2 ). In general, the models reproduce observations of CHBr 3 and CH 2 Br 2 obtained in the tropical tropopause layer (TTL) at various locations throughout the Pacific well. Zonal variability in VSLS loading in the TTL is generally consistent among models, with CHBr 3 (and to a lesser extent CH 2 Br 2 ) most elevated over the tropical western Pacific during boreal winter. The models also indicate the Asian monsoon during boreal summer to be an important pathway for VSLS reaching the stratosphere, though the strength of this signal varies considerably among models. We derive an ensemble climatological mean estimate of the stratospheric bromine SGI from CHBr 3 and CH 2 Br 2 of 2.0 (1.2–2.5) ppt,  ∼  57 % larger than the best estimate from the most recent World Meteorological Organization (WMO) Ozone Assessment Report. We find no evidence for a long-term, transport-driven trend in the stratospheric SGI of bromine over the simulation period. The transport-driven interannual variability in the annual mean bromine SGI is of the order of ±5 %, with SGI exhibiting a strong positive correlation with the El Niño–Southern Oscillation (ENSO) in the eastern Pacific. Overall, our results do not show systematic differences between models specific to the choice of reanalysis meteorology, rather clear differences are seen related to differences in the implementation of transport processes in the models.

Description: The first concerted multi-model intercomparison of halogenated very short-lived substances (VSLS) has been performed, within the framework of the ongoing Atmospheric Tracer Transport Model Intercomparison Project (TransCom). Eleven global models or model variants participated, simulating the major natural bromine VSLS, bromoform (CHBr3) and dibromomethane (CH2Br2), over a 20-year period (1993-2012). The overarching goal of TransCom-VSLS was to provide a reconciled model estimate of the stratospheric source gas injection (SGI) of bromine from these gases, to constrain the current measurement-derived range, and to investigate inter-model differences due to emissions and transport processes.Models ran with standardised idealised chemistry, to isolate differences due to transport, and we investigated the sensitivity of results to a range of VSLS emission inventories. Models were tested in their ability to reproduce the observed seasonal and spatial distribution of VSLS at the surface, using measurements from NOAA’s long-term global monitoring network, and in the tropical troposphere, using recent aircraft measurements - including high altitude observations from the NASA Global Hawk platform. The models generally capture the seasonal cycle of surface CHBr3 and CH2Br2 well, with a strong model-measurement correlation (r ≥ 0.7) and a low sensitivity to the choice of emission inventory, at most sites. In a given model, the absolute model-measurement agreement is highly sensitive to the choice of emissions and inter-model differences are also apparent, even when using the same inventory, highlighting the challenges faced in evaluating such inventories at the global scale. Across the ensemble, most consistency is found within the tropics where most of the models (8 out of 11) achieve optimal agreement to surface CHBr3 observations using the lowest of the three CHBr3 emission inventories tested (similarly, 8 out of 11 models for CH2 Br2). In general, the models are able to reproduce well observations of CHBr3 and CH2 Br2 obtained in the tropical tropopause layer (TTL) at various locations throughout the Pacific. Zonal variability in VSLS loading in the TTL is generally consistent among models, with CHBr3 (and to a lesser extent CH2 Br2) most elevated over the tropical West Pacific during boreal winter. The models also indicate the Asian Monsoon during boreal summer to be an important pathway for VSLS reaching the stratosphere, though the strength of this signal varies considerably among models. We derive an ensemble climatological mean estimate of the stratospheric bromine SGI from CHBr3 and CH2 Br2 of 2.0 (1.2-2.5) ppt, ≫ 57% larger than the best estimate from the most recent World Meteorological Organization (WMO) Ozone Assessment Report. We find no evidence for a long-term, transport-driven trend in the stratospheric SGI of bromine over the simulation period. However, transport-driven inter-annual variability in the annual mean bromine SGI is of the order of a ±5%, with SGI exhibiting a strong positive correlation with ENSO in the East Pacific.

Description: Biogenic halocarbons from the Peruvian upwelling region as tropospheric halogen source Helmke Hepach, Birgit Quack, Susann Tegtmeier, Anja Engel, Astrid Bracher, Steffen Fuhlbrügge, Luisa Galgani, Elliot L. Atlas, Johannes Lampel, Udo Frieß, and Kirstin Krüger Atmos. Chem. Phys., 16, 12219-12237, doi:10.5194/acp-16-12219-2016, 2016 We present surface seawater measurements of bromo- and iodocarbons, which are involved in numerous atmospheric processes such as tropospheric and stratospheric ozone chemistry, from the highly productive Peruvian upwelling. By combining trace gas measurements, characterization of organic matter and phytoplankton species, and tropospheric modelling, we show that large amounts of iodocarbons produced from the pool of organic matter may contribute strongly to local tropospheric iodine loading.

Description: Halocarbons, halogenated short-chained hydrocarbons, are produced naturally in the oceans by biological and chemical processes. They are emitted from surface seawater into the atmosphere, where they take part in numerous chemical processes such as ozone destruction and the oxidation of mercury and dimethyl sulfide. Here we present oceanic and atmospheric halocarbon data for the Peruvian upwelling obtained during the M91 cruise onboard the research vessel Meteor in December 2012. Surface waters during the cruise were characterized by moderate concentrations of bromoform (CHBr3) and dibromomethane (CH2Br2) correlating with diatom biomass derived from marker pigment concentrations, which suggests this phytoplankton group as likely source. Concentrations measured for the iodinated compounds methyl iodide (CH3I) of up to 35.4 pmol L−1, chloroiodomethane (CH2ClI) of up to 58.1 pmol L−1 and diiodomethane (CH2I2) of up to 32.4 pmol L−1 in water samples were much higher than previously reported for the tropical Atlantic upwelling systems. Iodocarbons also correlated with the diatom biomass and even more significantly with dissolved organic matter (DOM) components measured in the surface water. Our results suggest a biological source of these compounds as significant driving factor for the observed large iodocarbon concentrations. Elevated atmospheric mixing ratios of CH3I (up to 3.2 ppt), CH2ClI (up to 2.5 ppt) and CH2I2 (3.3 ppt) above the upwelling were correlated with seawater concentrations and high sea-to-air fluxes. The enhanced iodocarbon production in the Peruvian upwelling contributed significantly to tropospheric iodine levels.

Description: Chemical composition, microstructure, and hygroscopic properties of aerosol particles at the Zotino Tall Tower Observatory (ZOTTO), Siberia, during a summer campaign Atmospheric Chemistry and Physics Discussions, 15, 7837-7893, 2015 Author(s): E. F. Mikhailov, G. N. Mironov, C. Pöhlker, X. Chi, M. L. Krüger, M. Shiraiwa, J.-D. Förster, U. Pöschl, S. S. Vlasenko, T. I. Ryshkevich, M. Weigand, A. L. D. Kilcoyne, and M. O. Andreae In this study we describe the hygroscopic properties of accumulation- and coarse-mode aerosol particles sampled at the Zotino Tall Tower Observatory (ZOTTO) in Central Siberia (61° N; 89° E) from 16 to 21 June 2013. The hygroscopic growth measurements were supplemented with chemical analyses of the samples, including inorganic ions and organic/elemental carbon. In addition, the microstructure and chemical composition of aerosol particles were analyzed by X-ray micro-spectroscopy (STXM-NEXAFS) and transmission electron microscopy (TEM). A mass closure analysis indicates that organic carbon accounted for 61 and 38% of PM in the accumulation mode and coarse mode, respectively. The water soluble fraction of organic matter was estimated to be 52 and 8% of PM in these modes. Sulfate, predominantly in the form of ammoniated sulfate, was the dominant inorganic component in both size modes: ∼34% in the accumulation vs. ∼47% in the coarse mode. The hygroscopic growth measurements were conducted with a filter-based differential hygroscopicity analyzer (FDHA) over the range of 5–99.4% RH in the hydration and dehydration operation modes. The FDHA study indicates that both accumulation and coarse modes exhibit pronounced water uptake approximately at the same RH, starting at ∼70%, while efflorescence occurred at different humidities, i.e., at ∼35% RH for submicron particles vs. ∼50% RH for supermicron particles. This ∼15% RH difference was attributed to higher content of organic material in the submicron particles, which suppresses water release in the dehydration experiments. The kappa mass interaction model (KIM) was applied to characterize and parameterize non-ideal solution behavior and concentration-dependent water uptake by atmospheric aerosol samples in the 5–99.4% RH range. Based on KIM, the volume-based hygroscopicity parameter, κ v , was calculated. The κ v, ws value related to the water soluble (ws) fraction was estimated to be ∼0.15 for the accumulation mode and ∼0.36 for the coarse mode, respectively. The obtained κ v, ws for the accumulation mode is in good agreement with earlier data reported for remote sites in the Amazon rain forest (κ v ≈ 0.15) and a Colorado boreal forest (κ v ≈ 0.16). We used the Zdanovskii–Stokes–Robinson (ZSR) mixing rule to predict the chemical composition dependent hygroscopicity, κ v, p . The obtained κ v, p values overestimate the experimental FDHA-KIM-derived κ v, ws by factors of 1.8 and 1.5 for the accumulation and coarse modes, respectively. This divergence can be partly explained by incomplete dissolution of the hygroscopic inorganic compounds resulting from kinetic limitations due to a sparingly soluble organic coating. The TEM and STXM-NEXAFS results indicate that aged submicron (〉300 nm) and supermicron aerosol particles possess core-shell structures with an inorganic core, and are enriched in organic carbon at the mixed particle surface. The direct FDHA kinetic studies provide a bulk diffusion coefficient of water of ∼10 −12 cm 2 s −1 indicating a semi-solid state of the organic-rich phase leading to kinetic limitations of water uptake and release during hydration and dehydration cycles. Overall the present ZOTTO data set, obtained in the growing season, has revealed a strong influence of organic carbon on the hygroscopic properties of the ambient aerosols. The sparingly soluble organic coating controls hygroscopic growth, phase transitions, and microstructural rearrangement processes. The observed kinetic limitations can strongly influence the outcome of experiments performed on multi-second time scales, such as the commonly applied HTDMA (Hygroscopicity Tandem Differential Mobility Analyzer) and CCNC (Cloud Condensation Nuclei Counter) measurements.

Description: In this study we describe the hygroscopic properties of accumulation- and coarse-mode aerosol particles sampled at the Zotino Tall Tower Observatory (ZOTTO) in Central Siberia (61° N; 89° E) from 16 to 21 June 2013. The hygroscopic growth measurements were supplemented with chemical analyses of the samples, including inorganic ions and organic/elemental carbon. In addition, the microstructure and chemical composition of aerosol particles were analyzed by X-ray micro-spectroscopy (STXM-NEXAFS) and transmission electron microscopy (TEM). A mass closure analysis indicates that organic carbon accounted for 61 and 38% of PM in the accumulation mode and coarse mode, respectively. The water soluble fraction of organic matter was estimated to be 52 and 8% of PM in these modes. Sulfate, predominantly in the form of ammoniated sulfate, was the dominant inorganic component in both size modes: ∼34% in the accumulation vs. ∼47% in the coarse mode. The hygroscopic growth measurements were conducted with a filter-based differential hygroscopicity analyzer (FDHA) over the range of 5–99.4% RH in the hydration and dehydration operation modes. The FDHA study indicates that both accumulation and coarse modes exhibit pronounced water uptake approximately at the same RH, starting at ∼70%, while efflorescence occurred at different humidities, i.e., at ∼35% RH for submicron particles vs. ∼50% RH for supermicron particles. This ∼15% RH difference was attributed to higher content of organic material in the submicron particles, which suppresses water release in the dehydration experiments. The kappa mass interaction model (KIM) was applied to characterize and parameterize non-ideal solution behavior and concentration-dependent water uptake by atmospheric aerosol samples in the 5–99.4% RH range. Based on KIM, the volume-based hygroscopicity parameter, κv, was calculated. The κv, ws value related to the water soluble (ws) fraction was estimated to be ∼0.15 for the accumulation mode and ∼0.36 for the coarse mode, respectively. The obtained κv, ws for the accumulation mode is in good agreement with earlier data reported for remote sites in the Amazon rain forest (κv ≈ 0.15) and a Colorado boreal forest (κv ≈ 0.16). We used the Zdanovskii–Stokes–Robinson (ZSR) mixing rule to predict the chemical composition dependent hygroscopicity, κv, p. The obtained κv, p values overestimate the experimental FDHA-KIM-derived κv, ws by factors of 1.8 and 1.5 for the accumulation and coarse modes, respectively. This divergence can be partly explained by incomplete dissolution of the hygroscopic inorganic compounds resulting from kinetic limitations due to a sparingly soluble organic coating. The TEM and STXM-NEXAFS results indicate that aged submicron (〉300 nm) and supermicron aerosol particles possess core-shell structures with an inorganic core, and are enriched in organic carbon at the mixed particle surface. The direct FDHA kinetic studies provide a bulk diffusion coefficient of water of ∼10−12 cm2 s−1 indicating a semi-solid state of the organic-rich phase leading to kinetic limitations of water uptake and release during hydration and dehydration cycles. Overall the present ZOTTO data set, obtained in the growing season, has revealed a strong influence of organic carbon on the hygroscopic properties of the ambient aerosols. The sparingly soluble organic coating controls hygroscopic growth, phase transitions, and microstructural rearrangement processes. The observed kinetic limitations can strongly influence the outcome of experiments performed on multi-second time scales, such as the commonly applied HTDMA (Hygroscopicity Tandem Differential Mobility Analyzer) and CCNC (Cloud Condensation Nuclei Counter) measurements.

Description: The purpose of this study is to investigate horizontal transport processes in the winter stratosphere using data with a high spatial and temporal resolution. For this reason the Freie Universität Berlin Climate Middle Atmosphere Model (FUB-CMAM) with its model top at 83 km altitude, increased horizontal resolution T42 and the semi-Lagrangian transport scheme for advecting passive tracers is used. A new result of this paper is the classification of specific transport phenomena within the stratosphere into tropical-subtropical streamer (e.g. Offermann et al., 1999) and polar vortex extrusions hereafter called polar vortex streamers. To investigate the role played by these large-scale structures on the inter-annual and seasonal variability of the observed negative ozone trend in northern mid-latitudes, the global occurrence of such streamers were calculated based on a 10-year model climatology, concentrating on the existence of the Arctic polar vortex. For the identification and counting of streamers, the new method of zonal anomaly was chosen, which in comparison to other methods produced the best result in this study. The analysis of the months October–May yielded a maximum occurrence of tropical-subtropical streamers during Arctic winter and spring in the middle and upper stratosphere. Synoptic maps revealed highest intensities in the subtropics over East Asia with a secondary maximum over the Atlantic in the northern hemisphere. Furthermore, tropical-subtropical streamers exhibited about a four times higher occurrence than polar vortex streamers, indicating that the subtropical barrier is more permeable than the polar vortex barrier (edge) in the model, which is in good correspondence with observations (e.g. Plumb, 2002; Neu et al., 2003). Interesting for the total ozone loss in mid-latitudes is the consideration of the lower stratosphere, where strongest ozone depletion is observed at polar latitudes (WMO, 2003). In this particular region the FUB-CMAM simulated a climatological maximum of 10% occurrence of tropical-subtropical streamers over East-Asia/West Pacific and the Atlantic during early- and mid-winter. The results of this paper demonstrate that the regular occurrence of stratospheric streamers e.g., large-scale mixing processes of tropical-subtropical and polar vortex air masses into mid-latitudes, could play a significant role on the strength and variability of the observed total ozone decrease at mid-latitudes and should not be neglected in future climate change studies.

Description: Dimethylsulphide (DMS) emissions from the West Pacific Ocean: a potential marine source for the stratospheric sulphur layer Atmospheric Chemistry and Physics Discussions, 12, 30543-30570, 2012 Author(s): C. A. Marandino, S. Tegtmeier, K. Krüger, C. Zindler, E. L. Atlas, F. Moore, and H. W. Bange Sea surface and atmospheric measurements of dimethylsulphide (DMS) were performed during the TransBrom cruise in the West Pacific Ocean between Japan and Australia in October 2009. Air-sea DMS fluxes were computed between 0 and 30 μmol m −2 d −1 , which are in agreement with those computed by the current climatology, and peak emissions of marine DMS into the atmosphere were found during the occurrence of tropical storm systems. Atmospheric variability in DMS, however, did not follow that of the computed fluxes and was more related to atmospheric transport processes. The computed emissions were used as input fields for the Langrangian dispersion model FLEXPART, which was set up with actual meteorological fields from ERA-interim data and different chemical lifetimes of DMS. A comparison with aircraft in-situ data from the adjacent HIPPO2 campaign revealed an overall good agreement between modeled versus observed DMS profiles over the tropical West Pacific ocean. Based on observed DMS emissions and the meteorological fields over the cruise track region, the model projected that up to 30 g S per month in the form of DMS can be transported above 17 km in this region. This surprisingly large DMS entrainment into the stratosphere is disproportionate to the regional extent of the cruise track area and mainly due to the high convective activity in this region as simulated by the transport model. Thus, we conclude that the considerably larger area of the tropical West Pacific Ocean can be an important source of sulphur to the stratospheric persistent sulphur layer, which has not been considered as yet.

Description: Sea surface and atmospheric measurements of dimethylsulphide (DMS) were performed during the TransBrom cruise in the West Pacific Ocean between Japan and Australia in October 2009. Air-sea DMS fluxes were computed between 0 and 30 μmol m−2 d−1, which are in agreement with those computed by the current climatology, and peak emissions of marine DMS into the atmosphere were found during the occurrence of tropical storm systems. Atmospheric variability in DMS, however, did not follow that of the computed fluxes and was more related to atmospheric transport processes. The computed emissions were used as input fields for the Langrangian dispersion model FLEXPART, which was set up with actual meteorological fields from ERA-interim data and different chemical lifetimes of DMS. A comparison with aircraft in-situ data from the adjacent HIPPO2 campaign revealed an overall good agreement between modeled versus observed DMS profiles over the tropical West Pacific ocean. Based on observed DMS emissions and the meteorological fields over the cruise track region, the model projected that up to 30 g S per month in the form of DMS can be transported above 17 km in this region. This surprisingly large DMS entrainment into the stratosphere is disproportionate to the regional extent of the cruise track area and mainly due to the high convective activity in this region as simulated by the transport model. Thus, we conclude that the considerably larger area of the tropical West Pacific Ocean can be an important source of sulphur to the stratospheric persistent sulphur layer, which has not been considered as yet.

Description: Direct oceanic emissions unlikely to account for the missing source of atmospheric carbonyl sulfide Sinikka T. Lennartz, Christa A. Marandino, Marc von Hobe, Pau Cortes, Birgit Quack, Rafel Simo, Dennis Booge, Andrea Pozzer, Tobias Steinhoff, Damian L. Arevalo-Martinez, Corinna Kloss, Astrid Bracher, Rüdiger Röttgers, Elliot Atlas, and Kirstin Krüger Atmos. Chem. Phys., 17, 385-402, doi:10.5194/acp-17-385-2017, 2017 We present new sea surface and marine boundary layer measurements of carbonyl sulfide, the most abundant sulfur gas in the atmosphere, and calculate an oceanic emission estimate. Our results imply that oceanic emissions are very unlikely to account for the missing source in the atmospheric budget that is currently discussed for OCS.

Description: Drivers of diel and regional variations of halocarbon emissions from the tropical North East Atlantic Atmospheric Chemistry and Physics Discussions, 13, 19701-19750, 2013 Author(s): H. Hepach, B. Quack, F. Ziska, S. Fuhlbrügge, E. L. Atlas, I. Peeken, K. Krüger, and D. W. R. Wallace Methyl iodide (CH 3 I}, bromoform (CHBr 3 ) and dibromomethane (CH 2 Br 2 ), which are produced naturally in the oceans, take part in ozone chemistry both in the troposphere and the stratosphere. The significance of oceanic upwelling regions for emissions of these trace gases in the global context is still uncertain although they have been identified as important source regions. To better quantify the role of upwelling areas in current and future climate, this paper analyzes major factors that influenced halocarbon emissions from the tropical North East Atlantic including the Mauritanian upwelling during the DRIVE expedition. Diel and regional variability of oceanic and atmospheric CH 3 I, CHBr 3 and CH 2 Br 2 was determined along with biological and meteorological parameters at six 24 h-stations. Low oceanic concentrations of CH 3I from 0.1–5.4 pmol L -1 were equally distributed throughout the investigation area. CHBr 3 of 1.0–42.4 pmol L -1 and CH 2 Br 2 of 1.0–9.4 pmol L -1 were measured with maximum concentrations close to the Mauritanian coast. Atmospheric mixing rations of CH 3 I of up to 3.3, CHBr 3 to 8.9 and CH 2 Br 2 to 3.1 ppt above the upwelling and 1.8, 12.8, respectively 2.2 ppt at a Cape Verdean coast were detected during the campaign. While diel variability in CH 3 I emissions could be mainly ascribed to oceanic non-biological production, no main driver was identified for its emissions in the entire study region. In contrast, oceanic bromocarbons resulted from biogenic sources which were identified as regional drivers of their sea-to-air fluxes. The diel impact of wind speed on bromocarbon emissions increased with decreasing distance to the coast. The height of the marine atmospheric boundary layer (MABL) was determined as an additional factor influencing halocarbon emissions. Oceanic and atmospheric halocarbons correlated well in the study region and in combination with high oceanic CH 3I , CHBr 3 and CH 2 Br 2 concentrations, local hot spots of atmospheric halocarbons could solely be explained by marine sources. This conclusion is in contrast with previous studies that hypothesized the occurrence of elevated atmospheric halocarbons over the eastern tropical Atlantic mainly originating from the West-African continent.

Description: Methyl iodide (CH3I}, bromoform (CHBr3) and dibromomethane (CH2Br2), which are produced naturally in the oceans, take part in ozone chemistry both in the troposphere and the stratosphere. The significance of oceanic upwelling regions for emissions of these trace gases in the global context is still uncertain although they have been identified as important source regions. To better quantify the role of upwelling areas in current and future climate, this paper analyzes major factors that influenced halocarbon emissions from the tropical North East Atlantic including the Mauritanian upwelling during the DRIVE expedition. Diel and regional variability of oceanic and atmospheric CH3I, CHBr3 and CH2Br2 was determined along with biological and meteorological parameters at six 24 h-stations. Low oceanic concentrations of CH3I from 0.1–5.4 pmol L-1 were equally distributed throughout the investigation area. CHBr3 of 1.0–42.4 pmol L-1 and CH2Br2 of 1.0–9.4 pmol L-1 were measured with maximum concentrations close to the Mauritanian coast. Atmospheric mixing rations of CH3I of up to 3.3, CHBr3 to 8.9 and CH2Br2 to 3.1 ppt above the upwelling and 1.8, 12.8, respectively 2.2 ppt at a Cape Verdean coast were detected during the campaign. While diel variability in CH3I emissions could be mainly ascribed to oceanic non-biological production, no main driver was identified for its emissions in the entire study region. In contrast, oceanic bromocarbons resulted from biogenic sources which were identified as regional drivers of their sea-to-air fluxes. The diel impact of wind speed on bromocarbon emissions increased with decreasing distance to the coast. The height of the marine atmospheric boundary layer (MABL) was determined as an additional factor influencing halocarbon emissions. Oceanic and atmospheric halocarbons correlated well in the study region and in combination with high oceanic CH3I, CHBr3 and CH2Br2 concentrations, local hot spots of atmospheric halocarbons could solely be explained by marine sources. This conclusion is in contrast with previous studies that hypothesized the occurrence of elevated atmospheric halocarbons over the eastern tropical Atlantic mainly originating from the West-African continent.

Description: Global sea-to-air flux climatology for bromoform, dibromomethane and methyl iodide Atmospheric Chemistry and Physics Discussions, 13, 5601-5648, 2013 Author(s): F. Ziska, B. Quack, K. Abrahamsson, S. D. Archer, E. Atlas, T. Bell, J. H. Butler, L. J. Carpenter, C. E. Jones, N. R. P. Harris, H. Hepach, K. G. Heumann, C. Hughes, J. Kuss, K. Krüger, P. Liss, R. M. Moore, A. Orlikowska, S. Raimund, C. E. Reeves, W. Reifenhäuser, A. D. Robinson, C. Schall, T. Tanhua, S. Tegtmeier, S. Turner, L. Wang, D. Wallace, J. Williams, H. Yamamoto, S. Yvon-Lewis, and Y. Yokouchi Volatile halogenated organic compounds containing bromine and iodine, which are naturally produced in the ocean, are involved in ozone depletion in both the troposphere and stratosphere. Three prominent compounds transporting large amounts of marine halogens into the atmosphere are bromoform (CHBr 3 ), dibromomethane (CH 2 Br 2 ) and methyl iodide (CH 3 I). The input of marine halogens to the stratosphere is based on observations and modeling studies using low resolution oceanic emission scenarios derived from top down approaches. In order to improve emission inventory estimates, we calculate data-based high resolution global sea-to-air flux estimates of these compounds from surface observations within the HalOcAt database ( https://halocat.geomar.de/ ). Global maps of marine and atmospheric surface concentrations are derived from the data which are divided into coastal, shelf and open ocean regions. Considering physical and biogeochemical characteristics of ocean and atmosphere, the open ocean water and atmosphere data are classified into 21 regions. The available data are interpolated onto a 1° × 1° grid while missing grid values are interpolated with latitudinal and longitudinal dependent regression techniques reflecting the compounds' distributions. With the generated surface concentration climatologies for the ocean and atmosphere, global concentration gradients and sea-to-air fluxes are calculated. Based on these calculations we estimate a total global flux of 1.5/2.5 Gmol Br yr −1 for CHBr 3 , 0.78/0.98 Gmol Br yr −1 for CH 2 Br 2 and 1.24/1.45 Gmol I yr −1 for CH 3 I (Robust Fit/Ordinary Least Square regression technique). Contrary to recent studies, negative fluxes occur in each sea-to-air flux climatology, mainly in the Arctic and Antarctic region. "Hot spots" for global polybromomethane emissions are located in the equatorial region, whereas methyl iodide emissions are enhanced in the subtropical gyre regions. Inter-annual and seasonal variation is contained within our calculations for all three compounds. Compared to earlier studies, our global fluxes are at the lower end of estimates, especially for bromoform. An underrepresentation of coastal emissions and of extreme events in our estimate might explain the mismatch between our bottom up emission estimate and top down approaches.

Description: Volatile halogenated organic compounds containing bromine and iodine, which are naturally produced in the ocean, are involved in ozone depletion in both the troposphere and stratosphere. Three prominent compounds transporting large amounts of marine halogens into the atmosphere are bromoform (CHBr3), dibromomethane (CH2Br2) and methyl iodide (CH3I). The input of marine halogens to the stratosphere is based on observations and modeling studies using low resolution oceanic emission scenarios derived from top down approaches. In order to improve emission inventory estimates, we calculate data-based high resolution global sea-to-air flux estimates of these compounds from surface observations within the HalOcAt database (https://halocat.geomar.de/). Global maps of marine and atmospheric surface concentrations are derived from the data which are divided into coastal, shelf and open ocean regions. Considering physical and biogeochemical characteristics of ocean and atmosphere, the open ocean water and atmosphere data are classified into 21 regions. The available data are interpolated onto a 1° × 1° grid while missing grid values are interpolated with latitudinal and longitudinal dependent regression techniques reflecting the compounds' distributions. With the generated surface concentration climatologies for the ocean and atmosphere, global concentration gradients and sea-to-air fluxes are calculated. Based on these calculations we estimate a total global flux of 1.5/2.5 Gmol Br yr−1 for CHBr3, 0.78/0.98 Gmol Br yr−1 for CH2Br2 and 1.24/1.45 Gmol I yr−1 for CH3I (Robust Fit/Ordinary Least Square regression technique). Contrary to recent studies, negative fluxes occur in each sea-to-air flux climatology, mainly in the Arctic and Antarctic region. "Hot spots" for global polybromomethane emissions are located in the equatorial region, whereas methyl iodide emissions are enhanced in the subtropical gyre regions. Inter-annual and seasonal variation is contained within our calculations for all three compounds. Compared to earlier studies, our global fluxes are at the lower end of estimates, especially for bromoform. An underrepresentation of coastal emissions and of extreme events in our estimate might explain the mismatch between our bottom up emission estimate and top down approaches.

Description: Black carbon (BC) aerosols are influencing the Earth’s atmosphere and climate, but their microphysical properties, spatiotemporal distribution and long-range transport are not well constrained. This study analyzes the transatlantic transport of BC-rich African biomass burning (BB) pollution into the Amazon Basin, based on airborne observations of aerosol particles and trace gases in and off the Brazilian coast during the ACRIDICON-CHUVA campaign in September 2014, combining in-situ measurements on the research aircraft HALO with satellite remote-sensing and numerical model results. During flight AC19 over land and ocean at the Brazilian coastline in the northeast of the Amazon Basin, we observed a BC-rich atmospheric layer at ~ 3.5 km altitude with a vertical extension of ~ 0.3 km. Backward trajectory analyses suggest that fires in African grasslands, savannas, and shrublands were the main source of this pollution layer, and that the observed BB smoke had undergone more than 10 days of atmospheric transport and aging. The BC mass concentrations in the layer ranged from 0.5 to 2 μg m−3, and the BC particle number fraction of ~ 40 % was about 8 times higher than observed in a fresh Amazonian BB plume, representing the highest value ever observed in the region. Upon entering the Amazon Basin, the layer started to broaden and to subside, due to convective mixing and entrainment of the BB aerosol into the boundary layer. Satellite observations show that the transatlantic transport of pollution layers is a frequently occurring process, seasonally peaking in August/September. By analyzing the aircraft observations within the broader context of the long-term data from the Amazon Tall Tower Observatory (ATTO), we found that the transatlantic transport of African BB smoke layers has a strong impact on the north-central Amazonian aerosol population during the BB-influenced season (July to November). Specifically, the early BB season in this part of the Amazon appears to be dominated by African smoke, whereas the later BB season appears to be dominated by South American fires. This dichotomy is reflected in pronounced changes of aerosol optical properties such as the single scattering albedo (increasing from 0.85 in August to 0.90 in November) and the BC-to-CO enhancement ratio (decreasing from 7.4 to 4.4 ng m−3 ppb−1). Our results suggest that, despite the high amount of BC particles, the African BB aerosol act as efficient cloud condensation nuclei (CCN) with potentially important implications for aerosol-cloud interactions and the hydrological cycle in the Amazon Basin.

Description: Introduction to the SPARC Reanalysis Intercomparison Project (S-RIP) and overview of the reanalysis systems Masatomo Fujiwara, Jonathon S. Wright, Gloria L. Manney, Lesley J. Gray, James Anstey, Thomas Birner, Sean Davis, Edwin P. Gerber, V. Lynn Harvey, Michaela I. Hegglin, Cameron R. Homeyer, John A. Knox, Kirstin Krüger, Alyn Lambert, Craig S. Long, Patrick Martineau, Beatriz M. Monge-Sanz, Michelle L. Santee, Susann Tegtmeier, Simon Chabrillat, David G. H. Tan, David R. Jackson, Saroja Polavarapu, Gilbert P. Compo, Rossana Dragani, Wesley Ebisuzaki, Yayoi Harada, Chiaki Kobayashi, Will McCarty, Kazutoshi Onogi, Steven Pawson, Adrian Simmons, Krzysztof Wargan, Jeffrey S. Whitaker, and Cheng-Zhi Zou Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-652,2016 Manuscript under review for ACP (discussion: open, 0 comments) We introduce the SPARC Reanalysis Intercomparison Project (S-RIP), review key concepts and elements of atmospheric reanalysis systems, and summarize the technical details of and differences among eleven of these systems. Our primary objective is to collect these items into a single reference that supports and streamlines scientific studies and intercomparisons of reanalysis products. We also address several common misunderstandings and points of confusion regarding reanalysis data sets.

Description: The climate research community uses atmospheric reanalysis data sets to understand a wide range of processes and variability in the atmosphere, yet different reanalyses may give very different results for the same diagnostics. The Stratosphere–troposphere Processes And their Role in Climate (SPARC) Reanalysis Intercomparison Project (S-RIP) is a coordinated activity to compare reanalysis data sets using a variety of key diagnostics. The objectives of this project are to identify differences among reanalyses and understand their underlying causes, to provide guidance on appropriate usage of various reanalysis products in scientific studies, particularly those of relevance to SPARC, and to contribute to future improvements in the reanalysis products by establishing collaborative links between reanalysis centres and data users. The project focuses predominantly on differences among reanalyses, although studies that include operational analyses and studies comparing reanalyses with observations are also included when appropriate. The emphasis is on diagnostics of the upper troposphere, stratosphere, and lower mesosphere. This overview paper for the S-RIP special issue summarizes the motivation and goals of the S-RIP activity, and reviews key technical aspects of the reanalysis data sets that are the focus of the S-RIP report.

Description: Introduction to the SPARC Reanalysis Intercomparison Project (S-RIP) and overview of the reanalysis systems Masatomo Fujiwara, Jonathon S. Wright, Gloria L. Manney, Lesley J. Gray, James Anstey, Thomas Birner, Sean Davis, Edwin P. Gerber, V. Lynn Harvey, Michaela I. Hegglin, Cameron R. Homeyer, John A. Knox, Kirstin Krüger, Alyn Lambert, Craig S. Long, Patrick Martineau, Andrea Molod, Beatriz M. Monge-Sanz, Michelle L. Santee, Susann Tegtmeier, Simon Chabrillat, David G. H. Tan, David R. Jackson, Saroja Polavarapu, Gilbert P. Compo, Rossana Dragani, Wesley Ebisuzaki, Yayoi Harada, Chiaki Kobayashi, Will McCarty, Kazutoshi Onogi, Steven Pawson, Adrian Simmons, Krzysztof Wargan, Jeffrey S. Whitaker, and Cheng-Zhi Zou Atmos. Chem. Phys., 17, 1417-1452, doi:10.5194/acp-17-1417-2017, 2017 We introduce the SPARC Reanalysis Intercomparison Project (S-RIP), review key concepts and elements of atmospheric reanalysis systems, and summarize the technical details of and differences among 11 of these systems. This work supports scientific studies and intercomparisons of reanalysis products by collecting these background materials and technical details into a single reference. We also address several common misunderstandings and points of confusion regarding reanalyses.

Description: Modelling the chemistry and transport of bromoform within a sea breeze driven convective system during the SHIVA Campaign Atmospheric Chemistry and Physics Discussions, 13, 20611-20676, 2013 Author(s): P. D. Hamer, V. Marécal, R. Hossaini, M. Pirre, N. Warwick, M. Chipperfield, A. A. Samah, N. Harris, A. Robinson, B. Quack, A. Engel, K. Krüger, E. Atlas, K. Subramaniam, D. Oram, E. Leedham, G. Mills, K. Pfeilsticker, S. Sala, T. Keber, H. Bönisch, L. K. Peng, M. S. M. Nadzir, P. T. Lim, A. Mujahid, A. Anton, H. Schlager, V. Catoire, G. Krysztofiak, S. Fühlbrügge, M. Dorf, and W. T. Sturges We carry out a case study of the transport and chemistry of bromoform and its product gases (PGs) in a sea breeze driven convective episode on 19 November 2011 along the North West coast of Borneo during the "Stratospheric ozone: Halogen Impacts in a Varying Atmosphere" (SHIVA) campaign. We use ground based, ship, aircraft and balloon sonde observations made during the campaign, and a 3-D regional online transport and chemistry model capable of resolving clouds and convection explicitly that includes detailed bromine chemistry. The model simulates the temperature, wind speed, wind direction fairly well for the most part, and adequately captures the convection location, timing, and intensity. The simulated transport of bromoform from the boundary layer up to 12 km compares well to aircraft observations to support our conclusions. The model makes several predictions regarding bromine transport from the boundary layer to the level of convective detrainment (11 to 12 km). First, the majority of bromine undergoes this transport as bromoform. Second, insoluble organic bromine carbonyl species are transported to between 11 and 12 km, but only form a small proportion of the transported bromine. Third, soluble bromine species, which include bromine organic peroxides, hydrobromic acid (HBr), and hypobromous acid (HOBr), are washed out efficiently within the core of the convective column. Fourth, insoluble inorganic bromine species (principally Br 2 ) are not washed out of the convective column, but are also not transported to the altitude of detrainment in large quantities. We expect that Br 2 will make a larger relative contribution to the total vertical transport of bromine atoms in scenarios with higher CHBr 3 mixing ratios in the boundary layer, which have been observed in other regions. Finally, given the highly detailed description of the chemistry, transport and washout of bromine compounds within our simulations, we make a series of recommendations about the physical and chemical processes that should be represented in 3-D chemical transport models (CTMs) and chemistry climate models (CCMs), which are the primary theoretical means of estimating the contribution made by CHBr 3 and other very short-lived substances (VSLS) to the stratospheric bromine budget.

Description: We carry out a case study of the transport and chemistry of bromoform and its product gases (PGs) in a sea breeze driven convective episode on 19 November 2011 along the North West coast of Borneo during the "Stratospheric ozone: Halogen Impacts in a Varying Atmosphere" (SHIVA) campaign. We use ground based, ship, aircraft and balloon sonde observations made during the campaign, and a 3-D regional online transport and chemistry model capable of resolving clouds and convection explicitly that includes detailed bromine chemistry. The model simulates the temperature, wind speed, wind direction fairly well for the most part, and adequately captures the convection location, timing, and intensity. The simulated transport of bromoform from the boundary layer up to 12 km compares well to aircraft observations to support our conclusions. The model makes several predictions regarding bromine transport from the boundary layer to the level of convective detrainment (11 to 12 km). First, the majority of bromine undergoes this transport as bromoform. Second, insoluble organic bromine carbonyl species are transported to between 11 and 12 km, but only form a small proportion of the transported bromine. Third, soluble bromine species, which include bromine organic peroxides, hydrobromic acid (HBr), and hypobromous acid (HOBr), are washed out efficiently within the core of the convective column. Fourth, insoluble inorganic bromine species (principally Br2) are not washed out of the convective column, but are also not transported to the altitude of detrainment in large quantities. We expect that Br2 will make a larger relative contribution to the total vertical transport of bromine atoms in scenarios with higher CHBr3 mixing ratios in the boundary layer, which have been observed in other regions. Finally, given the highly detailed description of the chemistry, transport and washout of bromine compounds within our simulations, we make a series of recommendations about the physical and chemical processes that should be represented in 3-D chemical transport models (CTMs) and chemistry climate models (CCMs), which are the primary theoretical means of estimating the contribution made by CHBr3 and other very short-lived substances (VSLS) to the stratospheric bromine budget.

Description: Oceanic emissions unlikely to account for the missing source of atmospheric carbonyl sulfide Sinikka T. Lennartz, Christa A. Marandino, Marc von Hobe, Pau Cortes, Birgit Quack, Rafel Simo, Dennis Booge, Andrea Pozzer, Tobias Steinhoff, Damian L. Arevalo-Martinez, Corinna Kloss, Astrid Bracher, Rüdiger Röttgers, Elliott Atlas, and Kirstin Krüger Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-778,2016 Manuscript under review for ACP (discussion: open, 0 comments) We present new sea surface and marine boundary layer measurements of carbonyl sulfide, the most abundant sulfur gas in the atmosphere, and calculate an oceanic emission estimate. Our results imply that oceanic emissions are very unlikely to account for the missing source in the atmospheric budget that is currently discussed for OCS.

Description: The climate active trace-gas carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere. A missing source in its atmospheric budget is currently suggested, resulting from an upward revision of the vegetation sink in top-down approaches. Oceanic emissions have been proposed to close the resulting gap in the atmospheric budget. We present a bottom-up approach including new observations of OCS in surface waters of the tropical Atlantic, Pacific and Indian oceans to show that direct OCS emissions are insufficient to account for the missing source. Extrapolation of our observations using a biogeochemical box model suggests oceanic net uptake instead of emission for the entire tropical ocean area and, further, a global ocean source strength well below that suggested by top-down estimates. This bottom-up estimate of oceanic emissions has implications for using OCS as a proxy for terrestrial CO2 uptake, which is currently hampered by the inadequate quantification of atmospheric OCS sources and sinks.

Description: The Amazon Tall Tower Observatory (ATTO) in the remote Amazon Basin: overview of first results from ecosystem ecology, meteorology, trace gas, and aerosol measurements Atmospheric Chemistry and Physics Discussions, 15, 11599-11726, 2015 Author(s): M. O. Andreae, O. C. Acevedo, A. Araùjo, P. Artaxo, C. G. G. Barbosa, H. M. J. Barbosa, J. Brito, S. Carbone, X. Chi, B. B. L. Cintra, N. F. da Silva, N. L. Dias, C. Q. Dias-Júnior, F. Ditas, R. Ditz, A. F. L. Godoi, R. H. M. Godoi, M. Heimann, T. Hoffmann, J. Kesselmeier, T. Könemann, M. L. Krüger, J. V. Lavric, A. O. Manzi, D. Moran-Zuloaga, A. C. Nölscher, D. Santos Nogueira, M. T. F. Piedade, C. Pöhlker, U. Pöschl, L. V. Rizzo, C.-U. Ro, N. Ruckteschler, L. D. A. Sá, M. D. O. Sá, C. B. Sales, R. M. N. D. Santos, J. Saturno, J. Schöngart, M. Sörgel, C. M. de Souza, R. A. F. de Souza, H. Su, N. Targhetta, J. Tóta, I. Trebs, S. Trumbore, A. van Eijck, D. Walter, Z. Wang, B. Weber, J. Williams, J. Winderlich, F. Wittmann, S. Wolff, and A. M. Yáñez-Serrano The Amazon Basin plays key roles in the carbon and water cycles, climate change, atmospheric chemistry, and biodiversity. It already has been changed significantly by human activities, and more pervasive change is expected to occur in the next decades. It is therefore essential to establish long-term measurement sites that provide a baseline record of present-day climatic, biogeochemical, and atmospheric conditions and that will be operated over coming decades to monitor change in the Amazon region as human perturbations increase in the future. The Amazon Tall Tower Observatory (ATTO) has been set up in a pristine rain forest region in the central Amazon Basin, about 150 km northeast of the city of Manaus. An ecological survey including a biodiversity assessment has been conducted in the forest region surrounding the site. Two 80 m towers have been operated at the site since 2012, and a 325 m tower is nearing completion in mid-2015. Measurements of micrometeorological and atmospheric chemical variables were initiated in 2012, and their range has continued to broaden over the last few years. The meteorological and micrometeorological measurements include temperature and wind profiles, precipitation, water and energy fluxes, turbulence components, soil temperature profiles and soil heat fluxes, radiation fluxes, and visibility. A tree has been instrumented to measure stem profiles of temperature, light intensity, and water content in cryptogamic covers. The trace gas measurements comprise continuous monitoring of carbon dioxide, carbon monoxide, methane, and ozone at 5 to 8 different heights, complemented by a variety of additional species measured during intensive campaigns (e.g., VOC, NO, NO 2 , and OH reactivity). Aerosol optical, microphysical, and chemical measurements are made above the canopy as well as in the canopy space. They include light scattering and absorption, aerosol fluorescence, number and volume size distributions, chemical composition, cloud condensation nuclei (CCN) concentrations, and hygroscopicity. Initial results from ecological, meteorological, and chemical studies at the ATTO site are presented in this paper.

Description: The Amazon Basin plays key roles in the carbon and water cycles, climate change, atmospheric chemistry, and biodiversity. It already has been changed significantly by human activities, and more pervasive change is expected to occur in the next decades. It is therefore essential to establish long-term measurement sites that provide a baseline record of present-day climatic, biogeochemical, and atmospheric conditions and that will be operated over coming decades to monitor change in the Amazon region as human perturbations increase in the future. The Amazon Tall Tower Observatory (ATTO) has been set up in a pristine rain forest region in the central Amazon Basin, about 150 km northeast of the city of Manaus. An ecological survey including a biodiversity assessment has been conducted in the forest region surrounding the site. Two 80 m towers have been operated at the site since 2012, and a 325 m tower is nearing completion in mid-2015. Measurements of micrometeorological and atmospheric chemical variables were initiated in 2012, and their range has continued to broaden over the last few years. The meteorological and micrometeorological measurements include temperature and wind profiles, precipitation, water and energy fluxes, turbulence components, soil temperature profiles and soil heat fluxes, radiation fluxes, and visibility. A tree has been instrumented to measure stem profiles of temperature, light intensity, and water content in cryptogamic covers. The trace gas measurements comprise continuous monitoring of carbon dioxide, carbon monoxide, methane, and ozone at 5 to 8 different heights, complemented by a variety of additional species measured during intensive campaigns (e.g., VOC, NO, NO2, and OH reactivity). Aerosol optical, microphysical, and chemical measurements are made above the canopy as well as in the canopy space. They include light scattering and absorption, aerosol fluorescence, number and volume size distributions, chemical composition, cloud condensation nuclei (CCN) concentrations, and hygroscopicity. Initial results from ecological, meteorological, and chemical studies at the ATTO site are presented in this paper.

Description: The contribution of oceanic halocarbons to marine and free troposphere air over the tropical West Pacific Atmospheric Chemistry and Physics Discussions, 15, 17887-17943, 2015 Author(s): S. Fuhlbrügge, B. Quack, S. Tegtmeier, E. Atlas, H. Hepach, Q. Shi, S. Raimund, and K. Krüger Emissions of halogenated very short lived substances (VSLS) from the tropical oceans contribute to the atmospheric halogen budget and affect tropospheric and stratospheric ozone. Here we investigate the contribution of natural oceanic VSLS emissions to the Marine Atmospheric Boundary Layer (MABL) and their transport into the Free Troposphere (FT) over the tropical West Pacific. The study concentrates in particular on ship and aircraft measurements of the VSLS bromoform, dibromomethane and methyl iodide and meteorological parameters during the SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) campaign in the South China and Sulu Seas in November 2011. Elevated oceanic concentrations of 19.9 (2.80–136.91) pmol L −1 for bromoform, 5.0 (2.43–21.82) pmol L −1 for dibromomethane and 3.8 (0.55–18.83) pmol L −1 for methyl iodide in particular close to Singapore and at the coast of Borneo with high corresponding oceanic emissions of 1486 ± 1718 pmol m −2 h −1 for bromoform, 405 ± 349 pmol m −2 h −1 for dibromomethane and 433 ± 482 pmol m −2 h −1 for methyl iodide characterize this tropical region as a strong source of these compounds. Unexpectedly atmospheric mixing ratios in the MABL were relatively low with 2.08 ± 2.08 ppt for bromoform, 1.17 ± 1.17 ppt for dibromomethane and 0.39 ± 0.09 ppt for methyl iodide. We use meteorological and chemical ship and aircraft observations, FLEXPART trajectory calculations and source-loss estimates to identify the oceanic VSLS contribution to the MABL and to the FT. Our results show that a convective, well-ventilated MABL and intense convection led to the low atmospheric mixing ratios in the MABL despite the high oceanic emissions in coastal areas of the South-China and Sulu Seas. While the accumulated bromoform in the FT above the region origins almost entirely from the local South China Sea area, dibromomethane is largely advected from distant source regions. The accumulated FT mixing ratio of methyl iodide is higher than can be explained with the local oceanic or MABL contributions. Possible reasons, uncertainties and consequences of our observations and model estimates are discussed.

Description: Emissions of halogenated very short lived substances (VSLS) from the tropical oceans contribute to the atmospheric halogen budget and affect tropospheric and stratospheric ozone. Here we investigate the contribution of natural oceanic VSLS emissions to the Marine Atmospheric Boundary Layer (MABL) and their transport into the Free Troposphere (FT) over the tropical West Pacific. The study concentrates in particular on ship and aircraft measurements of the VSLS bromoform, dibromomethane and methyl iodide and meteorological parameters during the SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) campaign in the South China and Sulu Seas in November 2011. Elevated oceanic concentrations of 19.9 (2.80–136.91) pmol L−1 for bromoform, 5.0 (2.43–21.82) pmol L−1 for dibromomethane and 3.8 (0.55–18.83) pmol L−1 for methyl iodide in particular close to Singapore and at the coast of Borneo with high corresponding oceanic emissions of 1486 ± 1718 pmol m−2 h−1 for bromoform, 405 ± 349 pmol m−2 h−1 for dibromomethane and 433 ± 482 pmol m−2 h−1 for methyl iodide characterize this tropical region as a strong source of these compounds. Unexpectedly atmospheric mixing ratios in the MABL were relatively low with 2.08 ± 2.08 ppt for bromoform, 1.17 ± 1.17 ppt for dibromomethane and 0.39 ± 0.09 ppt for methyl iodide. We use meteorological and chemical ship and aircraft observations, FLEXPART trajectory calculations and source-loss estimates to identify the oceanic VSLS contribution to the MABL and to the FT. Our results show that a convective, well-ventilated MABL and intense convection led to the low atmospheric mixing ratios in the MABL despite the high oceanic emissions in coastal areas of the South-China and Sulu Seas. While the accumulated bromoform in the FT above the region origins almost entirely from the local South China Sea area, dibromomethane is largely advected from distant source regions. The accumulated FT mixing ratio of methyl iodide is higher than can be explained with the local oceanic or MABL contributions. Possible reasons, uncertainties and consequences of our observations and model estimates are discussed.

Description: The first three Canadian Arctic Atmospheric Chemistry Experiment (ACE) Validation Campaigns at Eureka (80° N, 86° W) were during two extremes of Arctic winter variability: Stratospheric sudden warmings (SSWs) in 2004 and 2006 were among the strongest, most prolonged on record; 2005 was a record cold winter. New satellite measurements from ACE-Fourier Transform Spectrometer (ACE-FTS), Sounding of the Atmosphere using Broadband Emission Radiometry, and Aura Microwave Limb Sounder (MLS), with meteorological analyses and Eureka lidar and radiosonde temperatures, are used to detail the meteorology in these winters, to demonstrate its influence on transport and chemistry, and to provide a context for interpretation of campaign observations. During the 2004 and 2006 SSWs, the vortex broke down throughout the stratosphere, reformed quickly in the upper stratosphere, and remained weak in the middle and lower stratosphere. The stratopause reformed at very high altitude, above where it could be accurately represented in the meteorological analyses. The 2004 and 2006 Eureka campaigns were during the recovery from the SSWs, with the redeveloping vortex over Eureka. 2005 was the coldest winter on record in the lower stratosphere, but with an early final warming in mid-March. The vortex was over Eureka at the start of the 2005 campaign, but moved away as it broke up. Disparate temperature profile structure and vortex evolution resulted in much lower (higher) temperatures in the upper (lower) stratosphere in 2004 and 2006 than in 2005. Satellite temperatures agree well with Eureka radiosondes, and with lidar data up to 50–60 km. Consistent with a strong, cold upper stratospheric vortex and enhanced radiative cooling after the SSWs, MLS and ACE-FTS trace gas measurements show strongly enhanced descent in the upper stratospheric vortex during the 2004 and 2006 Eureka campaigns compared to that in 2005.