Sulfur chemistry over the central Arctic Ocean during the summer: Gas‐to‐particle transformation

Abstract

Atmospheric gas‐to‐particle transformation of the oxidation products of dimethyl sulfide (DMS) was investigated over the central Arctic Ocean by using observational data and a coupled gas phase chemistry‐aerosol dynamics model. Chemical compounds investigated were sulfuric acid (H₂SO₄(g)), methasulfonic acid (MSA(g)), and sulfur dioxide (SO₂(g)) in the gas phase, and non‐sea‐salt sulfate (nss‐SO₄²⁻) and MSA in the particulate phase. During the advection from the open ocean to over the pack ice region, the particulate phase was found to be influenced significantly by three processes: (1) rapid removal of particulate matter during the first 1–2 days of advection, (2) continual formation of particulate nss‐SO₄²⁻ and MSA, and (3) local production of particles consisting mostly of matter other than nss‐SO₄²⁻ and MSA over the pack ice. In the absence of clouds and fogs, the principal sink for the vapors H₂SO₄(g) and MSA(g) were their condensational transport to submicron particles. SO₂(g) was influenced significantly by both dry deposition and gas phase oxidation. Although there is a local source of coarse sea‐salt particles within the pack ice region, the role of these particles in the budgets of nss‐SO₄²⁻ and SO₂(g), and probably also in the budget of MSA, is only minor, especially when compared with marine regions at lower latitudes. The performance of the DMS gas‐phase chemistry scheme was tested against field data using a measurement case influenced minimally by clouds/fogs and the free troposphere. The predicted concentration of nss‐SO₄²⁻ was within the uncertainties of the analysis, whereas that of MSA was high by a factor of 3–6. This demonstrates that not only heterogeneous reactions involved in atmospheric DMS chemistry but also certain gas‐phase reactions require further investigation.