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Discussion papers | Copyright
https://doi.org/10.5194/acp-2017-949
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Dec 2017

Research article | 11 Dec 2017

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This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

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, UK
  • 4University of Miami, Florida, USA
  • 5Centre for Atmospheric Informatics and Emissions Technology, Cranfield University, Cranfield, UK
  • 6University 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. 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 capture 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±0.3×108g/month and 0.7±0.1×108g/month for CHBr3 and CH2Br2 over 130°–155°E and 0°–12°N, respectively, which represent reductions of 20–40% and substantial spatial deviations from the a priori inventory. We find no evidence to support a robust linear relationship between CHBr3 and CH2Br2 oceanic emissions, as used by previous studies.

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Liang Feng et al.
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