Investigation of the Wintertime Transport of Reactive Trace Gases from East Asia into the Deep Tropics

Unprecedented growth of East Asian economies has led to increases of anthropogenic pollutants in the regional atmosphere. This pollutant burden is transported into the global atmosphere and is a significant source of intercontinental and transboundary anthropogenic pollution. This work analyzes pollution transport into the western Pacific associated with the dispersion of East Asian pollution during Northern Hemisphere winter. To examine transport characteristics, we use chemical and dynamical data sets obtained during the CONvective TRansport of Active Species in the Tropics (CONTRAST) field campaign, conducted from Guam during January&ndash;February 2014. We identify that the evolution of shear lines from decaying cold fronts and their southward advancement facilitates polluted air transport into low latitudes of the Western Pacific Ocean. Observations from two cases of shear line passage are analyzed. The result shows that this transport process significantly elevates anthropogenic trace gases in the marine boundary layer and lowermost free troposphere up to 3&ndash;4 km. Results of our analysis show that chemical influence of the shear line on the background tropical marine atmosphere varies as a function of pollution source, intensity, shear line strength, and the speed of advancement, as well as local background conditions. To quantify the contribution of shear-line-related transport, we introduce an index, the Anthropogenic Enhancement Factor (AEF), defined as a fractional change in mixing ratio of a gas brought about by the advancing front. This index shows that the most significant enhancements are for species with photochemical lifetimes comparable to their transport times from source regions.</p

Quantifying the vertical transport of CHBr&lt;sub&gt;3&lt;/sub&gt; and CH&lt;sub&gt;2&lt;/sub&gt;Br&lt;sub&gt;2&lt;/sub&gt; over the Western Pacific

We use the GEOS-Chem global 3-D atmospheric chemistry transport model to interpret atmospheric observations of bromoform (CHBr 3 ) and dibromomethane (CH 2 Br 2 ) collected during the CAST and CONTRAST aircraft measurement campaigns over the Western Pacific, January-February, 2014. We use a new linearised, tagged version of CHBr 3 and CH 2 Br 2 , allowing us to study the influence of emissions from specific geographical regions on observed atmospheric variations. The model describes 32 %-37 % of CHBr 3 observed variability and 15 %-45 % of CH 2 Br 2 observed variability during CAST and CONTRAST, reflecting errors in vertical model transport. The model has a mean positive bias of 30 % that is larger near the surface reflecting errors in the poorly constrained prior emission estimates. We find using the model that observed variability of CHBr 3 and CH 2 Br 2 is driven by ocean emissions, particularly by the open ocean above which there is deep convection. We find that contributions from coastal oceans and terrestrial sources over the Western Pacific are significant above altitudes > 6 km, but is still dominated by the open ocean emissions and by air masses transported over longer time lines than the campaign period. In the absence of reliable ocean emission estimates, we use a new physical age of air simulation to determine the relative abundance of halogens delivered by CHBr 3 and CH 2 Br 2 to the tropical transition layer (TTL). We find that 6 % (47 %) of air masses with halogen released by the ocean reach the TTL within two (three) atmospheric e-folding lifetimes of CHBr 3 and almost all of them reach the TTL within one e-folding lifetime of CH 2 Br 2 . We find these gases are delivered to the TTL by a small number of rapid convection events during the study period. Over the duration of CAST and CONTRAST and over our study region, oceans delivered a mean (range) CHBr 3 and CH 2 Br 2 mole fraction of 0.46 (0.13-0.72) and 0.88 (0.71-1.01) pptv, respectively, to the TTL, and a mean (range) Bry mole fraction of 3.14 (1.81-4.18) pptv to the upper troposphere. Open ocean emissions are responsible for 75 % of these values, with only 8 % from coastal oceans

Brominated compounds at the tropical tropopause

Very short-lived brominated substances (VSLBr) are an important source of stratospheric bromine, an effective ozone destruction catalyst. However, the accurate estimation of the organic and inorganic partitioning of bromine and the input to the stratosphere remains uncertain. Here, we report near-tropopause measurements of organic brominated substances found over the tropical Pacific during the NASA Airborne Tropical Tropopause Experiment campaigns. We combine aircraft observations and a chemistry-climate model to quantify the total bromine loading injected to the stratosphere. Surprisingly, despite differences in vertical transport between the Eastern and Western Pacific, VSLBr (organic + inorganic) contribute approximately similar amounts of bromine [∼6 (4-9) parts per trillion] [corrected] to the stratospheric input at the tropical tropopause. These levels of bromine cause substantial ozone depletion in the lower stratosphere, and any increases in future abundances (e.g., as a result of aquaculture) will lead to larger depletions.This work was supported by NASA Grant NNX10AO83A S08 and NERC Grant NE/J006246/1. The National Center for Atmospheric Research (NCAR) is funded by the National Science Foundation NSF. Computing resources (ark:/85065/d7wd3xhc) were provided by the Climate Simulation Laboratory at NCAR’s Computational and Information Systems Laboratory (CISL), sponsored by the NSF and other agencies. The CESM project (which includes CAM-Chem) is supported by the NSF and the Office of Science (BER) of the US Department of Energy. This work was also sponsored by the NASA Atmospheric Composition Modeling and Analysis Program Activities (ACMAP), grant/cooperative agreement number NNX11AH90G.This is the author accepted manuscript. The final version is available from National Academy of Sciences via http://dx.doi.org/10.1073/pnas.151146311

BrO and inferred Bry profiles over the western Pacific : Relevance of inorganic bromine sources and a Bry minimum in the aged tropical tropopause layer

We report measurements of bromine monoxide (BrO) and use an observationally constrained chemical box model to infer total gas-phase inorganic bromine (Bry) over the tropical western Pacific Ocean (tWPO) during the CONTRAST field campaign (January-February 2014). The observed BrO and inferred Bry profiles peak in the marine boundary layer (MBL), suggesting the need for a bromine source from sea-salt aerosol (SSA), in addition to organic bromine (CBry). Both profiles are found to be C-shaped with local maxima in the upper free troposphere (FT). The median tropospheric BrO vertical column density (VCD) was measured as 1.6×1013 molec cm-2, compared to model predictions of 0.9×1013 molec cm-2 in GEOS-Chem (CBry but no SSA source), 0.4×1013 molec cm-2 in CAM-Chem (CBry and SSA), and 2.1×1013 molec cm-2 in GEOS-Chem (CBry and SSA). Neither global model fully captures the C-shape of the Bry profile. A local Bry maximum of 3.6 ppt (2.9-4.4 ppt; 95 % confidence interval, CI) is inferred between 9.5 and 13.5 km in air masses influenced by recent convective outflow. Unlike BrO, which increases from the convective tropical tropopause layer (TTL) to the aged TTL, gas-phase Bry decreases from the convective TTL to the aged TTL. Analysis of gas-phase Bry against multiple tracers (CFC-11, H2O-O3 ratio, and potential temperature) reveals a Bry minimum of 2.7 ppt (2.3-3.1 ppt; 95 % CI) in the aged TTL, which agrees closely with a stratospheric injection of 2.6 ± 0.6 ppt of inorganic Bry (estimated from CFC-11 correlations), and is remarkably insensitive to assumptions about heterogeneous chemistry. Bry increases to 6.3 ppt (5.6-7.0 ppt; 95 % CI) in the stratospheric "middleworld" and 6.9 ppt (6.5-7.3 ppt; 95 % CI) in the stratospheric "overworld". The local Bry minimum in the aged TTL is qualitatively (but not quantitatively) captured by CAM-Chem, and suggests a more complex partitioning of gas-phase and aerosol Bry species than previously recognized. Our data provide corroborating evidence that inorganic bromine sources (e.g., SSA-derived gas-phase Bry) are needed to explain the gas-phase Bry budget in the upper free troposphere and TTL. They are also consistent with observations of significant bromide in Upper Troposphere-Lower Stratosphere aerosols. The total Bry budget in the TTL is currently not closed, because of the lack of concurrent quantitative measurements of gas-phase Bry species (i.e., BrO, HOBr, HBr, etc.) and aerosol bromide. Such simultaneous measurements are needed to (1) quantify SSA-derived Bry in the upper FT, (2) test Bry partitioning, and possibly explain the gas-phase Bry minimum in the aged TTL, (3) constrain heterogeneous reaction rates of bromine, and (4) account for all of the sources of Bry to the lower stratosphere

The O2/N2 Ratio and CO2 Airborne Southern Ocean Study

The Southern Ocean plays a critical role in the global climate system by mediating atmosphere–ocean partitioning of heat and carbon dioxide. However, Earth system models are demonstrably deficient in the Southern Ocean, leading to large uncertainties in future air–sea CO2 flux projections under climate warming and incomplete interpretations of natural variability on interannual to geologic time scales. Here, we describe a recent aircraft observational campaign, the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study, which collected measurements over the Southern Ocean during January and February 2016. The primary research objective of the ORCAS campaign was to improve observational constraints on the seasonal exchange of atmospheric carbon dioxide and oxygen with the Southern Ocean. The campaign also included measurements of anthropogenic and marine biogenic reactive gases; high-resolution, hyperspectral ocean color imaging of the ocean surface; and microphysical data relevant for understanding and modeling cloud processes. In each of these components of the ORCAS project, the campaign has significantly expanded the amount of observational data available for this remote region. Ongoing research based on these observations will contribute to advancing our understanding of this climatically important system across a range of topics including carbon cycling, atmospheric chemistry and transport, and cloud physics. This article presents an overview of the scientific and methodological aspects of the ORCAS project and highlights early findings

The O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) Study

The Southern Ocean plays a critical role in the global climate system by mediating atmosphere–ocean partitioning of heat and carbon dioxide. However, Earth system models are demonstrably deficient in the Southern Ocean, leading to large uncertainties in future air–sea CO2 flux projections under climate warming and incomplete interpretations of natural variability on interannual to geologic time scales. Here, we describe a recent aircraft observational campaign, the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study, which collected measurements over the Southern Ocean during January and February 2016. The primary research objective of the ORCAS campaign was to improve observational constraints on the seasonal exchange of atmospheric carbon dioxide and oxygen with the Southern Ocean. The campaign also included measurements of anthropogenic and marine biogenic reactive gases; high-resolution, hyperspectral ocean color imaging of the ocean surface; and microphysical data relevant for understanding and modeling cloud processes. In each of these components of the ORCAS project, the campaign has significantly expanded the amount of observational data available for this remote region. Ongoing research based on these observations will contribute to advancing our understanding of this climatically important system across a range of topics including carbon cycling, atmospheric chemistry and transport, and cloud physics. This article presents an overview of the scientific and methodological aspects of the ORCAS project and highlights early findings

BrO and Bry profiles over the Western Pacific: Relevance of Inorganic Bromine Sources and a Bry Minimum in the Aged Tropical Tropopause Layer

We report measurements of bromine monoxide (BrO) and use an observationally constrained chemical box-model to infer total gas phase inorganic bromine (Bry) over the tropical Western Pacific Ocean (tWPO) during the CONTRAST field 40 campaign (January – February 2014). The median tropospheric BrO Vertical Column Density (VCD) over the tWPO was measured as 1.6×1013 molec. cm˗2, compared to model predictions of 0.4×1013 in CAM-Chem, 0.9×1013 in GEOS-Chem, and 2.1×1013 in GEOS-Chem with a sea-salt aerosol (SSA) bromine source. The observed BrO and inferred Bry profiles is found to be C-shaped in the troposphere, with local maxima in the marine boundary layer (MBL) and in the upper free troposphere. Neither global model fully captures this profile shape. Between 6 and 13.5 km, the inferred Bry is highly sensitive to 5 assumptions about the rate of heterogeneous bromine recycling (depends on the surface area of ice/aerosols), and the inclusion of a SSA bromine source. A local Bry maximum of 3.6 ppt (2.3-11.1 ppt, 95% CI) is observed between 9.5 and 13.5 km in air masses influenced by recent convective outflow. Unlike BrO, which increases from the convective TTL to the aged TTL, gas phase Bry decreases from the convective TTL to the aged TTL. Analysis of gas phase Bry against multiple tracers (CFC-11, H2O/O3 ratio, and θ) reveals a Bry minimum of 2.7 ppt (2.4-3.0 ppt, 95% CI) in the aged TTL, which is remarkably insensitive 10 to assumptions about heterogeneous chemistry. Bry increases to 6.3 ppt (5.9-6.7 ppt, 95% CI) in the stratospheric middleworld, and 6.9 ppt (6.7-7.1 ppt, 95% CI) in the stratospheric overworld. The local Bry minimum in the aged TTL is qualitatively (but not quantitatively) captured by CAM-chem, and suggests a more complex partitioning of gas phase and aerosol Bry species than previously recognized. Our data provide corroborating evidence that inorganic bromine sources (e.g., SSA derived gas phase Bry) are needed to explain the gas phase Bry budget in the TTL. They are also consistent with observations of significant 15 bromide in UTLS aerosols. The total Bry budget in the TTL is currently not closed, because of the lack of concurrent quantitative measurements of gas phase Bry species (i.e., BrO, HOBr, HBr, etc.) and aerosol bromide. These simultaneous measurements are needed 1) to quantify SSA derived Bry aloft, 2) to test Bry partitioning, and explain the gas phase Bry minimum in the aged TTL, 3) to constrain heterogeneous reaction rates of bromine, and 4) to account for all of the sources of Bry to the lower stratosphere.Fil: Koenig, Theodore K.. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados UnidosFil: Volkamer, Rainer. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados UnidosFil: Baidar, Sunil. Cooperative Institute for Research in Environmental Sciences; Estados Unidos. State University of Colorado at Boulder; Estados UnidosFil: Dix, Barbara. State University of Colorado at Boulder; Estados UnidosFil: Wang, Siyuan. State University of Colorado at Boulder; Estados Unidos. University of Michigan; Estados UnidosFil: Anderson, Daniel C.. University of Maryland. Department of Atmospheric and Oceanic Science; Estados UnidosFil: Salawitch, Ross J.. University of Maryland. Department of Atmospheric and Oceanic Science; Estados UnidosFil: Wales, Pamela A.. University of Maryland. Department of Atmospheric and Oceanic Science; Estados UnidosFil: Cuevas, Carlos A.. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Fernandez, Rafael Pedro. Universidad Nacional de Cuyo. Facultad de Ciencias Exactas y Naturales; Argentina. Universidad Tecnologica Nacional. Facultad Regional Mendoza. Secretaría de Ciencia, Tecnología y Postgrado; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza; ArgentinaFil: Saiz Lopez, Alfonso. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; EspañaFil: Evans, Mathew J.. University of York; Reino UnidoFil: Sherwen, Tomás. University of York; Reino UnidoFil: Jacob, Daniel J.. Harvard University; Estados UnidosFil: Schmidt, Johan. Universidad de Copenhagen; DinamarcaFil: Kinnison, Douglas. National Center for Atmospheric Research; Estados UnidosFil: Lamarque, Jean François. National Center for Atmospheric Research; Estados UnidosFil: Apel, Eric C.. National Center for Atmospheric Research; Estados UnidosFil: Bresch, James C.. National Center for Atmospheric Research; Estados UnidosFil: Campos, Teresa. National Center for Atmospheric Research; Estados UnidosFil: Flocke, Frank M.. National Center for Atmospheric Research; Estados UnidosFil: Hall, Samuel R.. National Center for Atmospheric Research; Estados UnidosFil: Honomichl, Shawn B.. National Center for Atmospheric Research; Estados UnidosFil: Hornbrook, Rebecca. National Center for Atmospheric Research; Estados UnidosFil: Jensen, Jorgen B.. National Center for Atmospheric Research; Estados UnidosFil: Lueb, Richard. National Center for Atmospheric Research; Estados UnidosFil: Montzka, Denise D.. National Center for Atmospheric Research; Estados UnidosFil: Pan, Laura L.. National Center for Atmospheric Research; Estados UnidosFil: Reeves, J. Michael. National Center for Atmospheric Research; Estados UnidosFil: Schauffle, Sue M.. National Center for Atmospheric Research; Estados UnidosFil: Ullmann, Kirk. National Center for Atmospheric Research; Estados UnidosFil: Weinheimer, Andrew J.. National Center for Atmospheric Research; Estados UnidosFil: Atlas, Elliot L.. University of Miami; Estados UnidosFil: Donets, Valeria. University of Miami; Estados UnidosFil: Maria A. Navarro. University of Miami; Estados UnidosFil: Riemer, Daniel. University of Miami; Estados UnidosFil: Blake, Nicola J.. University of California; Estados UnidosFil: Chen, Dexien. School of Earth & Atmospheric Sciences; Estados UnidosFil: Huey, L. Gregory. School of Earth & Atmospheric Sciences; Estados UnidosFil: Tanner, David J.. School of Earth & Atmospheric Sciences; Estados UnidosFil: Hanisco, Thomas F.. National Aeronautics and Space Administration; Estados UnidosFil: Wolfe, Glenn M.. University of Maryland; Estados Unidos. National Aeronautics and Space Administration; Estados Unido