Item

Abstract

Carbonyl sulfide (OCS) is the most abundant sulfur-containing gas in the Earth’s atmosphere playing a pivotal role as precursor to sulfate aerosol in the stratosphere. In the troposphere, dominant sources of OCS are oceans and anthropogenic emissions while consumption by the terrestrial biosphere is the largest sink. The marine environment is the dominant source region for OCS with comparisons between observations and models indicating that there is either an over-estimation of the terrestrial OCS sink or an unaccounted source over the tropical oceans.

New chemical paths have been found for the peroxy radical formed from the oxidation of dimethyl sulfide (DMS) by the OH radical that may impact the yield of OCS. We performed experiments in the atmospheric simulation chamber SAPHIR to elucidate the DMS oxidation chemical mechanism focusing on the paths leading to the formation of OCS. The experiments were performed at atmospherically relevant conditions initiating the DMS oxidation with OH and Cl radicals. During the experiments we collected measurements of precursors, radicals, OCS and oxidation products.

An unexpected high yield of 7% for OCS was found for all experimental conditions. Concentrations of measured species were compared to results from a detailed chemical mechanism, which includes new chemical paths derived a-priori from theoretical calculations. Despite the detailed chemistry included, model result largely underestimated the observed OCS. We suggest additional paths and adjustment of rate coefficients to bring our measurements and model results into agreement.