Enhanced Daytime Production of Airborne Pollutants by SO2 Oxidation at Ocean Surface Over Eastern Asia

Abstract

Sulfur dioxide (SO₂) is oxidized to sulfate within atmospheric aerosols. However, it is also deposited on the ocean surface by dry deposition thereby reacting with the enriched organic material within sea-surface microlayer (SML) such as unsaturated fatty acids and humic substances. Here, we performed dedicated experiments on SO₂ oxidation chemistry at authentic SML sampled from 10 sites in coastal area and open sea of the South China Sea, in dark and under simulated sunlight irradiation. Real-time measurements of volatile organic compounds (VOCs) formed by SO₂ oxidation chemistry were performed by using ultra-high resolution mass spectrometry. Intriguingly, a total of 104 product compounds were identified in dark whereas 843 compounds were produced upon sunlight irradiation, during the SO₂ oxidation of the SML samples. We evaluated the potential influence of the SO₂ oxidation on SML under light irradiation as a new marine VOCs source by a chemical transport model. The simulations suggest a significant change of oxygenated VOCs in marine atmosphere over Eastern Asia that potentially alters the budgets of HO_x and RO_x radicals and consequently the lifetime of methane.