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Volume 17, issue 24 | Copyright
Atmos. Chem. Phys., 17, 15245-15270, 2017
https://doi.org/10.5194/acp-17-15245-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 22 Dec 2017

Research article | 22 Dec 2017

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

Theodore K. Koenig1,2, Rainer Volkamer1,2, Sunil Baidar1,2,a, Barbara Dix1, Siyuan Wang2,3,b, Daniel C. Anderson4,c, Ross J. Salawitch4,5,6, Pamela A. Wales5, Carlos A. Cuevas7, Rafael P. Fernandez7,8, Alfonso Saiz-Lopez7, Mathew J. Evans9, Tomás Sherwen9, Daniel J. Jacob10,11, Johan Schmidt12, Douglas Kinnison13, Jean-François Lamarque13, Eric C. Apel13, James C. Bresch13, Teresa Campos13, Frank M. Flocke13, Samuel R. Hall13, Shawn B. Honomichl13, Rebecca Hornbrook13, Jørgen B. Jensen13, Richard Lueb13, Denise D. Montzka13, Laura L. Pan13, J. Michael Reeves13, Sue M. Schauffler13, Kirk Ullmann13, Andrew J. Weinheimer13, Elliot L. Atlas14, Valeria Donets14, Maria A. Navarro14, Daniel Riemer14, Nicola J. Blake15, Dexian Chen16,d, L. Gregory Huey16, David J. Tanner16, Thomas F. Hanisco17, and Glenn M. Wolfe17,18 Theodore K. Koenig et al.
  • 1Department of Chemistry & Biochemistry, University of Colorado, Boulder, CO, USA
  • 2Cooperative Institute for Research in Environmental Sciences (CIRES), Boulder, CO, USA
  • 3Department of Chemistry, University of Michigan, Ann Arbor, MI, USA
  • 4Department of Atmospheric & Oceanic Science, University of Maryland, College Park, MD, USA
  • 5Department of Chemistry & Biochemistry, University of Maryland, College Park, MD, USA
  • 6Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA
  • 7Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Rocasolano, Spanish National Research Council (CSIC), Madrid, Spain
  • 8Argentine National Research Council (CONICET), FCEN-UNCuyo, UNT-FRM, Mendoza, Argentina
  • 9Wolfson Atmospheric Chemistry Laboratories (WACL), Department of Chemistry, University of York, York, UK
  • 10John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • 11Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
  • 12Department of Chemistry, Copenhagen University, Copenhagen, Denmark
  • 13National Center for Atmospheric Research (NCAR), Boulder, CO, USA
  • 14Department of Atmospheric Science, Rosenstiel School of Marine & Atmospheric Sciences (RSMAS), University of Miami, Miami, FL, USA
  • 15Department of Chemistry, University of California, Irvine, CA, USA
  • 16School of Earth & Atmospheric Sciences, Georgia Tech, Atlanta, Georgia, USA
  • 17Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 18Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, MD, USA
  • anow at: Chemical Sciences Division, National Oceanic and Atmospheric Administration (NOAA), Boulder, CO, USA
  • bnow at: National Center for Atmospheric Research (NCAR), Boulder, CO, USA
  • cnow at: Department of Chemistry, University of Drexel, Philadelphia, PA, USA
  • dnow at: Department of Chemical Engineering, Carnegie Mellon University (CMU), Pittsburgh, PA, USA

Abstract. 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 1.6×1013moleccm−2, compared to model predictions of 0.9×1013moleccm−2 in GEOS-Chem (CBry but no SSA source), 0.4×1013moleccm−2 in CAM-Chem (CBry and SSA), and 2.1×1013moleccm−2 in GEOS-Chem (CBry and SSA). Neither global model fully captures the C-shape of the Bry profile. A local Bry maximum of 3.6ppt (2.9–4.4ppt; 95% confidence interval, CI) is inferred between 9.5 and 13.5km 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, H2OO3 ratio, and potential temperature) reveals a Bry minimum of 2.7ppt (2.3–3.1ppt; 95% CI) in the aged TTL, which agrees closely with a stratospheric injection of 2.6±0.6ppt of inorganic Bry (estimated from CFC-11 correlations), and is remarkably insensitive to assumptions about heterogeneous chemistry. Bry increases to 6.3ppt (5.6–7.0ppt; 95% CI) in the stratospheric "middleworld" and 6.9ppt (6.5–7.3ppt; 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.

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Tropospheric inorganic bromine (BrO and Bry) shows a C-shaped profile over the tropical western Pacific Ocean, and supports previous speculation that marine convection is a source for inorganic bromine from sea salt to the upper troposphere. The Bry profile in the tropical tropopause layer (TTL) is complex, suggesting that the total Bry budget in the TTL is not closed without considering aerosol bromide. The implications for atmospheric composition and bromine sources are discussed.
Tropospheric inorganic bromine (BrO and Bry) shows a C-shaped profile over the tropical western...
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