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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 20 | Copyright
Atmos. Chem. Phys., 18, 14787-14798, 2018
https://doi.org/10.5194/acp-18-14787-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Oct 2018

Research article | 15 Oct 2018

Surface fluxes of bromoform and dibromomethane over the tropical western Pacific inferred from airborne in situ measurements

Liang Feng1,2, Paul I. Palmer1,2, Robyn Butler2, Stephen J. Andrews3, Elliot L. Atlas4, Lucy J. Carpenter3, Valeria Donets4, Neil R. P. Harris5, Ross J. Salawitch6, Laura L. Pan7, and Sue M. Schauffler7 Liang Feng et al.
  • 1National Centre for Earth Observation, University of Edinburgh, Edinburgh, UK
  • 2School of GeoSciences, University of Edinburgh, Edinburgh, UK
  • 3Department of Chemistry, Wolfson Atmospheric Chemistry Laboratories, University of York, York, UK
  • 4Department of Atmospheric Science, University of Miami, Miami, Florida, USA
  • 5Centre for Atmospheric Informatics and Emissions Technology, Cranfield University, Cranfield, UK
  • 6Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Maryland, USA
  • 7National Center for Atmospheric Research, Boulder, Colorado, USA

Abstract. We infer surface fluxes of bromoform (CHBr3) and dibromoform (CH2Br2) from aircraft observations over the western Pacific using a tagged version of the GEOS-Chem global 3-D atmospheric chemistry model and a maximum a posteriori inverse model. Using GEOS-Chem (GC) as an intermediary, we find that the distribution of a priori ocean emissions of these gases are reasonably consistent with observed atmospheric mole fractions of CHBr3 (r = 0.62) and CH2Br2 (r = 0.38). These a priori emissions result in a positive model bias in CHBr3 peaking in the marine boundary layer, but reproduce observed values of CH2Br2 with no significant bias by virtue of its longer atmospheric lifetime. Using GEOS-Chem, we find that observed variations in atmospheric CHBr3 are determined equally by sources over the western Pacific and those outside the study region, but observed variations in CH2Br2 are determined mainly by sources outside the western Pacific. Numerical closed-loop experiments show that the spatial and temporal distribution of boundary layer aircraft data have the potential to substantially improve current knowledge of these fluxes, with improvements related to data density. Using the aircraft data, we estimate aggregated regional fluxes of 3.6±0.3×108 and 0.7±0.1×108gmonth−1 for CHBr3 and CH2Br2 over 130–155°E and 0–12°N, respectively, which represent reductions of 20%–40% of the prior inventories by Ordóñez et al. (2012) and substantial spatial deviations from different a priori inventories. We find no evidence to support a robust linear relationship between CHBr3 and CH2Br2 oceanic emissions, as used by previous studies. We find that over regions with dense observation coverage, our choice of a priori inventory does not significantly impact our reported a posteriori flux estimates.

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We infer surface fluxes of bromoform (CHBr3) and dibromoform (CH2Br2) from CAST and CONTRAST aircraft observations over the western Pacific, using a tagged version of the GEOS-Chem global 3-D atmospheric chemistry model and a Maximum A Posteriori inverse model. Using the aircraft data, we estimate the regional fluxes about 20–40 % smaller than the prior inventories by Ordóñez et al. (2012). We find no evidence to support a robust linear relationship between CHBr3 and CH2Br2 oceanic emissions.
We infer surface fluxes of bromoform (CHBr3) and dibromoform (CH2Br2) from CAST and CONTRAST...
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