Document Type

Article

Publication Date

12-22-2017

Publication Title

Atmospheric Chemistry and Physics

ISSN

1680-7324

Volume

17

Issue

24

DOI

http://dx.doi.org/10.5194/acp-17-15245-2017

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 1.6×1013 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.

Comments

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

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

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