A 3-DIMENSIONAL GLOBAL-MODEL STUDY OF CARBONYL SULFIDE IN THE TROPOSPHERE AND THE LOWER STRATOSPHERE

Global distributions of carbonyl sulfide and carbon disulfide have bee n calculated with a three-dimensional global model of the atmospheric general circulation (ECHAM). The model calculates a global sink streng th for carbonyl sulfide of 0.3 Tg S yr(-1), with vegetation uptake bei ng the largest sink. With this sink strength, the sources have to be c lose to the lower limit of the present estimate in the literature. The calculated mixing ratios are higher in the Southern Hemisphere than i n the Northern Hemisphere. This interhemispheric gradient is the oppos ite of what is observed demonstrating that the present knowledge of th e distribution of sinks and sources is not fully adequate. The model c alculations support the idea that the open oceans could act as a net s ink of carbonyl sulfide. The calculated stratospheric photolysis of ca rbonyl sulfide constitutes about 4% of the total sink of carbonyl sulf ide. A stratospheric production of sulfate from carbonyl sulfide of 0. 013 Tg S yr(-1) is obtained, which is 3 to 12 times less than what is needed to maintain the stratospheric sulfate aerosol layer. Although t hese results are associated with uncertainties, due to the low upper b oundary and coarse vertical resolution of the model, they support rece nt findings of a low stratospheric production of sulfate from carbonyl sulfide. instead, sulfur dioxide transported from the troposphere is calculated to be the most important precursor for the stratospheric su lfate aerosol layer.