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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-876
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Sep 2018

Research article | 11 Sep 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Sensitivity of Arctic sulfate aerosol and clouds to changes in future surface seawater dimethylsulfide concentrations

Rashed Mahmood1,2, Knut von Salzen1,2, Ann-Lise Norman3, Martí Galí4, and Maurice Levasseur5 Rashed Mahmood et al.
  • 1School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada
  • 2Canadian Center for Climate Modelling and Analysis, Environment and Climate Change Canada, Victoria, British Columbia, Canada
  • 3Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
  • 4Takuvik Joint International Laboratory & Québec-Océan, Université Laval, Québec, Québec, Canada
  • 5Département de biologie and Québec-Océan, Université Laval, Québec, Québec, Canada

Abstract. Dimethylsulfide (DMS), outgassed from ocean waters, plays an important role in the climate system, as it oxidizes to methane sulfonic acid (MSA) and sulfur dioxide (SO2), which can lead to the formation of sulfate aerosol. Newly formed sulfate aerosol resulting from DMS oxidation may grow by condensation of gases, in-cloud oxidation, and coagulation to sizes where they may act as cloud condensation nuclei (CCN) and influence cloud properties. Under future global warming conditions, sea-ice in the Arctic region is expected to decline significantly, which may lead to increased emissions of DMS from the open ocean and changes in cloud regimes. In this study we evaluate impacts of DMS on Arctic sulfate aerosol budget, changes in cloud droplet number concentration (CDNC), and cloud radiative forcing in the Arctic region under current and future sea ice conditions using an atmospheric global climate model. Given that future DMS concentrations are highly uncertain, several simulations with different surface seawater DMS concentrations and spatial distributions in the Arctic were performed in order to determine the sensitivity of sulfate aerosol budgets, CDNC, and cloud radiative forcing to Arctic surface seawater DMS concentrations. For any given amount and distribution of Arctic surface seawater DMS, similar amounts of sulfate are produced by oxidation of DMS in 2000 and 2050 despite large increases in DMS emission in the latter period due to sea ice retreat in the simulations. This relatively low sensitivity of sulfate burden is related to enhanced sulfate wet removal by precipitation in 2050. However simulated aerosol nucleation rates are higher in 2050, which results in an overall increase in CDNC and substantially more negative cloud radiative forcing. Thus potential future reductions in sea ice extent may cause cloud albedos to increase, resulting in a negative climate feedback on radiative forcing in the Arctic associated with ocean DMS emissions.

Rashed Mahmood et al.
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This study evaluates impacts of surface seawater dimethylsulfide on Arctic sulfate aerosol budget, changes in cloud droplet number concentration (CDNC), and cloud radiative forcing under current and future sea ice conditions using an atmospheric global climate model. In the future, sulfate wet removal efficiency is increased by enhanced precipitation, however, simulated aerosol nucleation rates are higher, which result in an overall increase in CDNC and negative cloud radiative forcing.
This study evaluates impacts of surface seawater dimethylsulfide on Arctic sulfate aerosol...
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