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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 Unidos Fil: Volkamer, Rainer. State University of Colorado at Boulder; Estados Unidos. Cooperative Institute for Research in Environmental Sciences; Estados Unidos Fil: Baidar, Sunil. Cooperative Institute for Research in Environmental Sciences; Estados Unidos. State University of Colorado at Boulder; Estados Unidos Fil: Dix, Barbara. State University of Colorado at Boulder; Estados Unidos Fil: Wang, Siyuan. State University of Colorado at Boulder; Estados Unidos. University of Michigan; Estados Unidos Fil: Anderson, Daniel C.. University of Maryland. Department of Atmospheric and Oceanic Science; Estados Unidos Fil: Salawitch, Ross J.. University of Maryland. Department of Atmospheric and Oceanic Science; Estados Unidos Fil: Wales, Pamela A.. University of Maryland. Department of Atmospheric and Oceanic Science; Estados Unidos Fil: Cuevas, Carlos A.. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; España Fil: 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; Argentina Fil: Saiz Lopez, Alfonso. Consejo Superior de Investigaciones Científicas. Instituto de Química Física; España Fil: Evans, Mathew J.. University of York; Reino Unido Fil: Sherwen, Tomás. University of York; Reino Unido Fil: Jacob, Daniel J.. Harvard University; Estados Unidos Fil: Schmidt, Johan. Universidad de Copenhagen; Dinamarca Fil: Kinnison, Douglas. National Center for Atmospheric Research; Estados Unidos Fil: Lamarque, Jean François. National Center for Atmospheric Research; Estados Unidos Fil: Apel, Eric C.. National Center for Atmospheric Research; Estados Unidos Fil: Bresch, James C.. National Center for Atmospheric Research; Estados Unidos Fil: Campos, Teresa. National Center for Atmospheric Research; Estados Unidos Fil: Flocke, Frank M.. National Center for Atmospheric Research; Estados Unidos Fil: Hall, Samuel R.. National Center for Atmospheric Research; Estados Unidos Fil: Honomichl, Shawn B.. National Center for Atmospheric Research; Estados Unidos Fil: Hornbrook, Rebecca. National Center for Atmospheric Research; Estados Unidos Fil: Jensen, Jorgen B.. National Center for Atmospheric Research; Estados Unidos Fil: Lueb, Richard. National Center for Atmospheric Research; Estados Unidos Fil: Montzka, Denise D.. National Center for Atmospheric Research; Estados Unidos Fil: Pan, Laura L.. National Center for Atmospheric Research; Estados Unidos Fil: Reeves, J. Michael. National Center for Atmospheric Research; Estados Unidos Fil: Schauffle, Sue M.. National Center for Atmospheric Research; Estados Unidos Fil: Ullmann, Kirk. National Center for Atmospheric Research; Estados Unidos Fil: Weinheimer, Andrew J.. National Center for Atmospheric Research; Estados Unidos Fil: Atlas, Elliot L.. University of Miami; Estados Unidos Fil: Donets, Valeria. University of Miami; Estados Unidos Fil: Maria A. Navarro. University of Miami; Estados Unidos Fil: Riemer, Daniel. University of Miami; Estados Unidos Fil: Blake, Nicola J.. University of California; Estados Unidos Fil: Chen, Dexien. School of Earth & Atmospheric Sciences; Estados Unidos Fil: Huey, L. Gregory. School of Earth & Atmospheric Sciences; Estados Unidos Fil: Tanner, David J.. School of Earth & Atmospheric Sciences; Estados Unidos Fil: Hanisco, Thomas F.. National Aeronautics and Space Administration; Estados Unidos Fil: Wolfe, Glenn M.. University of Maryland; Estados Unidos. National Aeronautics and Space Administration; Estados Unidos

Measurements of organic carbon compounds in both the gas and particle phases measured upwind, over and downwind of North America are synthesized to examine the total observed organic carbon (TOOC) over this region. These include measurements made aboard the NOAA WP-3 and BAe-146 aircraft, the NOAA research vessel Ronald H. Brown, and at the Thompson Farm and Chebogue Point surface sites during the summer 2004 ICARTT campaign. Both winter and summer 2002 measurements during the Pittsburgh Air Quality Study are also included. Lastly, the spring 2002 observations at Trinidad Head, CA, surface measurements made in March 2006 in Mexico City and coincidentally aboard the C-130 aircraft during the MILAGRO campaign and later during the IMPEX campaign off the northwestern United States are incorporated. Concentrations of TOOC in these datasets span more than two orders of magnitude. The daytime mean TOOC ranges from 4.0 to 456 μgC m−3 from the cleanest site (Trinidad Head) to the most polluted (Mexico City). Organic aerosol makes up 3–17% of this mean TOOC, with highest fractions reported over the northeastern United States, where organic aerosol can comprise up to 50% of TOOC. Carbon monoxide concentrations explain 46 to 86% of the variability in TOOC, with highest TOOC/CO slopes in regions with fresh anthropogenic influence, where we also expect the highest degree of mass closure for TOOC. Correlation with isoprene, formaldehyde, methyl vinyl ketene and methacrolein also indicates that biogenic activity contributes substantially to the variability of TOOC, yet these tracers of biogenic oxidation sources do not explain the variability in organic aerosol observed over North America. We highlight the critical need to develop measurement techniques to routinely detect total gas phase VOCs, and to deploy comprehensive suites of TOOC instruments in diverse environments to quantify the ambient evolution of organic carbon from source to sink.

International audience; Observations of CO2 were made in the upper troposphere and lower stratosphere in the deep tropics in order to determine the patterns of large-scale vertical transport and age of air in the Tropical Tropopause Layer (TTL). Flights aboard the NASA WB-57F aircraft over Central America and adjacent ocean areas took place in January and February, 2004 (Pre-AURA Validation Experiment, Pre-AVE) and 2006 (Costa Rice AVE, CR-AVE), and for the same flight dates of 2006, aboard the Proteus aircraft from the surface to 15 km over Darwin, Australia (Tropical Warm Pool International Cloud Experiment, TWP-ICE). The data demonstrate that the TTL is composed of two layers with distinctive features: (1) the lower TTL, 350?360 K (potential temperature(?); approximately 12?14 km), is subject to inputs of convective outflows, as indicated by layers of variable CO2 concentrations, with air parcels of zero age distributed throughout the layer; (2) the upper TTL, from ?=~360 K to ~390 K (14?18 km), ascends slowly and ages uniformly, as shown by a linear decline in CO2 mixing ratio tightly correlated with altitude, associated with increasing age. This division is confirmed by ensemble trajectory analysis. The CO2 concentration at the level of 360 K was 380.0(±0.2) ppmv, indistinguishable from surface site values in the Intertropical Convergence Zone (ITCZ) for the flight dates. Values declined with altitude to 379.2(±0.2) ppmv at 390 K, implying that air in the upper TTL monotonically ages while ascending. In combination with the winter slope of the CO2 seasonal cycle (+10.8±0.4 ppmv/yr), the vertical gradient of ?0.78 (±0.09) ppmv gives a mean age of 26(±3) days for the air at 390 K and a mean ascent rate of 1.5(±0.3) mm s?1. The TTL near 360 K in the Southern Hemisphere over Australia is very close in CO2 composition to the TTL in the Northern Hemisphere over Costa Rica, with strong contrasts emerging at lower altitudes (2 observed unexpected input from deep convection over Amazônia deep into the TTL. The CO2 data confirm the operation of a highly accurate tracer clock in the TTL that provides a direct measure of the ascent rate of the TTL and of the age of air entering the stratosphere.

The transport of very short-lived substances into the tropical upper troposphere and lower stratosphere is investigated by a three-dimensional chemical transport model using archived convective updraft mass fluxes (or detrainment rates) from the European Centre for Medium-Range Weather Forecast's ERA-Interim reanalysis. Large-scale vertical velocities are calculated from diabatic heating rates. With this approach we explicitly model the large scale subsidence in the tropical troposphere with convection taking place in fast and isolated updraft events. The model calculations agree generally well with observations of bromoform and methyl iodide from aircraft campaigns and with ozone and water vapor from sonde and satellite observations. Using a simplified treatment of dehydration and bromine product gas washout we give a range of 1.6 to 3 ppt for the contribution of bromoform to stratospheric bromine, assuming a uniform source in the boundary layer of 1 ppt. We show that the most effective region for VSLS transport into the stratosphere is the West Pacific, accounting for about 55% of the bromine from bromoform transported into the stratosphere under the supposition of a uniformly distributed source.