Isotopic constraints on the role of hypohalous acids in sulfate aerosol
formation in the remote marine boundary layer
Qianjie Chen1,Lei Geng1,a,b,Johan A. Schmidt2,Zhouqing Xie3,Hui Kang3,Jordi Dachs4,Jihong Cole-Dai5,Andrew J. Schauer6,Madeline G. Camp7,c,and Becky Alexander1Qianjie Chen et al. Qianjie Chen1,Lei Geng1,a,b,Johan A. Schmidt2,Zhouqing Xie3,Hui Kang3,Jordi Dachs4,Jihong Cole-Dai5,Andrew J. Schauer6,Madeline G. Camp7,c,and Becky Alexander1
1Department of Atmospheric Sciences, University of Washington,
Seattle, WA, USA
2Department of Chemistry, University of Copenhagen, Copenhagen,
Denmark
3Institute of Polar Environments, School of Earth and Space Sciences,
University of Science and Technology of China, Hefei, Anhui, China
4Department of Environmental Chemistry, IDAEA-CSIC, IDAEA-CSIC,
Barcelona, Catalunya, Spain
5Department of Chemistry and Biochemistry, South Dakota State
University, Brookings, SD, USA
6Department of Earth and Space Sciences, University of Washington,
Seattle, WA, USA
7Joint Institute for the Study of Atmosphere and Ocean, University of
Washington, Seattle, WA, USA
anow at: Univ. Grenoble-Alpes, LGGE, 38000, Grenoble,
France
bnow at: CNRS, LGGE, 38000, Grenoble, France
cnow at: DSG Solutions, LLC, Shoreline, WA, USA
1Department of Atmospheric Sciences, University of Washington,
Seattle, WA, USA
2Department of Chemistry, University of Copenhagen, Copenhagen,
Denmark
3Institute of Polar Environments, School of Earth and Space Sciences,
University of Science and Technology of China, Hefei, Anhui, China
4Department of Environmental Chemistry, IDAEA-CSIC, IDAEA-CSIC,
Barcelona, Catalunya, Spain
5Department of Chemistry and Biochemistry, South Dakota State
University, Brookings, SD, USA
6Department of Earth and Space Sciences, University of Washington,
Seattle, WA, USA
7Joint Institute for the Study of Atmosphere and Ocean, University of
Washington, Seattle, WA, USA
anow at: Univ. Grenoble-Alpes, LGGE, 38000, Grenoble,
France
bnow at: CNRS, LGGE, 38000, Grenoble, France
cnow at: DSG Solutions, LLC, Shoreline, WA, USA
Correspondence: Becky Alexander (beckya@atmos.washington.edu)
Received: 10 May 2016 – Discussion started: 12 May 2016 – Revised: 24 Aug 2016 – Accepted: 24 Aug 2016 – Published: 14 Sep 2016
Abstract. Sulfate is an important component of global atmospheric aerosol, and has partially compensated for greenhouse gas-induced warming during the industrial period. The magnitude of direct and indirect radiative forcing of aerosols since preindustrial times is a large uncertainty in climate models, which has been attributed largely to uncertainties in the preindustrial environment. Here, we report observations of the oxygen isotopic composition (Δ17O) of sulfate aerosol collected in the remote marine boundary layer (MBL) in spring and summer in order to evaluate sulfate production mechanisms in pristine-like environments. Model-aided analysis of the observations suggests that 33–50 % of sulfate in the MBL is formed via oxidation by hypohalous acids (HOX = HOBr + HOCl), a production mechanism typically excluded in large-scale models due to uncertainties in the reaction rates, which are due mainly to uncertainties in reactive halogen concentrations. Based on the estimated fraction of sulfate formed via HOX oxidation, we further estimate that daily-averaged HOX mixing ratios on the order of 0.01–0.1 parts per trillion (ppt = pmol/mol) in the remote MBL during spring and summer are sufficient to explain the observations.
The formation mechanisms of sulfate in the marine boundary layer are not well understood, which could result in large uncertainties in aerosol radiative forcing. We measure the oxygen isotopic composition (Δ17O) of sulfate collected in the MBL and analyze with a global transport model. Our results suggest that 33–50 % of MBL sulfate is formed via oxidation of S(IV) by hypohalous acids HOBr / HOCl in the aqueous phase, and the daily-mean HOBr/HOCl concentrations are on the order of 0.01–0.1 ppt.
The formation mechanisms of sulfate in the marine boundary layer are not well understood, which...
