Air-Sea Exchange of Sulphur and Nitrogen and Their Interaction in the Marine Atmosphere

Abstract

Compounds of sulphur and nitrogen can exchange across the sea surface in a number of chemical forms. In this paper we are principally concerned with formation and emission of gaseous compounds of these elements in and from seawater, as well as their subsequent reactivity and mutual interaction in the atmosphere. In the case of sulphur, the main gas formed in the oceans is dimethyl sulphide ({DMS)}, although other volatile compounds, such as carbonyl sulphide ({COS)}, are also of some importance both quantitatively and with respect to atmospheric chemistry. In the nitrogen system the major gaseous form is ammonia ({NH3)}, although mono-, di-, and tri-methylamines [N({CH3)n(H)3−n]} may also play some relatively minor role. In the atmosphere ammonia is the major gaseous source of alkali. For marine regions remote from pollution sources, the main products of {DMS} oxidation in the atmosphere, sulphur dioxide({SO2)/sulphate(SO4} 2−)/methanesulphonate({CH3SO3} −), are the major suppliers of acid to the atmospheric system. Thus, not unexpectedly, these two cycles constitute some of the major controls on the {pH} of rain and aerosols in remote marine areas (Charlson and Rodhe, 1982). Further, sub-micron particles formed from the interaction of {NH4} + and {SO4} 2− are very important as a source of cloud condensation nuclei in remote regions, and have also been proposed as a fundamental part of a natural climate regulating mechanism (Charlson et al., 1987).