资源环境科技发展态势分析平台

Hypohalous acids (HOCl + HOBr) play an important but highly uncertain role in sulfate aerosol production in the marine atmosphere due to the unmeasured reaction rate constants (k) of HOCl/HOBr and HSO3-, the dominant S(IV) species in acidified sea salt aerosols and cloudwater. We directly determined k(HOCl+HSO3) by investigating the kinetics of aqueous oxidation of dissolved SO2 by HOCl in low pH aerosol particles in a flow tube. Further, we predicted k(HOBr+HSO3) using a novel kinetics model developed from the HOCl/HSO3- results. k(HOBr+HSO3) and k(HOCl+HSO3) were estimated to be 2 and 3 orders of magnitude lower, respectively, than the values used in atmospheric models. We assess the importance of halogen-driven S(IV) oxidation in the marine atmosphere with this new fundamental understanding and find that in-cloud sulfate production via HOBr oxidation remains an important atmospheric process, but the HOCl oxidation pathway in acidified sea salt aerosols is unlikely to be important.

Plain Language Summary Atmospheric aerosol particles contribute to the direct and indirect forcing of the Earth's climate. A large portion of aerosol particle mass is sulfate, formed from chemical reactions involving the oxidation of sulfur dioxide. Significant uncertainties in assessing global radiative forcing arise from uncertainties in the formation mechanisms of sulfate aerosols in the marine atmosphere. Model studies have suggested that aqueous oxidation of sulfur dioxide by hypochlorous and hypobromous acids plays an important role in sulfate production in the marine atmosphere. However, the validity of thesemodel studies remains uncertain because the reaction rate constants of two key reactions-hypochlorous and hypobromous acids reacting with bisulfite-have never been experimentally measured. Here, we show with laboratory experiments that the reaction rate constant of hypochlorous acid with bisulfite is 3 orders of magnitude lower than that used in atmospheric models. A simple chemical kinetics model predicts that the reaction rate constant of hypobromous acid with bisulfite is 2 orders of magnitude lower than the value assumed in atmospheric models. As a result, sulfate production via the hypochlorous acid pathway in the marine atmosphere may not be as important as previously believed, while sulfate production through hypobromous acid reactions remains atmospherically important.