Dimethyl sulfide in the marine atmosphere

Abstract

We have performed over 900 measurements of atmospheric dimethyl sulfide (DMS) in five different marine locations: the equatorial Pacific; Cape Grim, Tasmania; the Bahamas; the North Atlantic; and the Sargasso Sea. At all locations, DMS concentrations were usually in the range of 100–400 ng S m −3 , with similar average concentrations of approximately 150 ng S m −3 (107 parts per thousand by volume). Highest concentrations occurred during, but were not limited to, periods of sustained high winds and overcast skies, presumably owing to faster exchange from surface seawater and less photochemical activity in the atmosphere. Lowest values occurred during airflow from continental regions, which provides higher levels of oxidants and free radicals to react with DMS. Averaged over time, the concentrations in clean marine air reached a maximum at night and a minimum in the afternoon, when concentrations were about one third lower than during the nighttime maximum. The observed concentrations of DMS in the marine atmosphere and their diurnal variability agree well with model simulations involving OH and NO 3 oxidation of DMS and are consistent with a global sea‐to‐air DMS flux of about 40±20 Tg S yr −1 . DMS may represent a major sink for NO 3 in the marine troposphere.