Climate Change

Biography

Biography: Agustin J. Colussi

Abstract

The oxidation of biogenic dimethyl sulfide (DMS) emissions is a global source of cloud condensation nuclei. The amounts of the nucleating H₂SO₄(g) species produced in such process, however, remain uncertain. Hydrophobic DMS is mostly oxidized in the gas-phase into H₂SO₄(g) + DMSO(g) (dimethyl sulfoxide), whereas water-soluble DMSO is oxidized into H2SO4(g) in the gas-phase but into SO42- + MeSO3- (methane sulfonate) on water surfaces. Thus, R = MeSO₃^-/non-sea-salt-SO₄^2- ratios would therefore gauge both the strength of DMS sources and the extent of DMSO heterogeneous oxidation if R_het = MeSO₃^-/SO₄^2- for DMSO(aq) + ·OH(g) were known. Here we report that R_het = 2.7, a value obtained from online electrospray mass spectra of DMSO(aq) + ·OH(g) reaction products, which quantifies the MeSO₃^- produced in DMSO heterogeneous oxidation on aqueous aerosols for the first time. On this basis, the inverse R-dependence on particle radius in size-segregated aerosol collected over Syowa station and Southern oceans is shown to be consistent with the competition between DMSO gas-phase oxidation and its mass accommodation followed by oxidation on aqueous droplets. Geographical R variations are thus associated with variable contributions of the heterogeneous pathway to DMSO atmospheric oxidation, which increase with the specific surface area of local aerosols.