Marine-derived carbonyl sulfide (COS), as a major component of volatile organic sulfur, greatly contributes to atmospheric sulfate formation especially in the stratosphere and affects the climate. Although photochemical formation pathways of COS from dissolved organic sulfur (DOS) in seawater have been extensively studied, the effect of nitrate on photoproduction of COS is still unknown. Herein, we report for the first time that enhanced nitrate concentration affects COS formation in the authentic seawater. By comparing the photochemical formation behaviors of COS from cysteine (a typical proxy of DOS) under different concentrations of nitrate during sunlight irradiation, we found that COS formation showed a trend of increasing first and then decreasing with the increase of nitrate concentration, which is closely related to nitrate photolysis. In addition, a common hydroxyl radical (•OH) scavengers (isopropyl alcohol) was used to evaluate in terms of its effect of •OH on the relative contribution of COS formation, and the results suggested that the generation of •OH with nitrate photolysis during the irradiation period plays a key role in the variation of COS formation. Our work suggests that the nitrate can be one of the most important controlling factors to impact on photochemical production of COS in surface seawater and effect of nitration concentration of photochemical processes should be considered.
 

Carbonyl sulfide,Nitrate,Seawater,Photochemistry,hydroxyl radicals