Modeling halogen chemistry in the marine boundary layer 2. Interactions with sulfur and the cloud-covered MBL

Abstract

A companion paper presented a numerical one-dimensional model of the marine boundary layer (MBL) including chemical reactions in the gas and aqueous phase, focusing on the reaction cycles of halogen compounds. In this paper we study interactions between halogen and sulfur chemistry. HOCl and HOBr were found to be generally more important than H2O2 or O3 in the oxidation of S(IV) in sea salt aerosols in the cloud-free MBL. The inclusion of halogen chemistry lead to an increase in the oxidation of DMS of roughly 63%. This additional oxidation is caused by BrO. The model was also expanded for the study of the cloudy MBL. We found that the effects of stratiform clouds on the evolution and diurnal cycle of halogen species are widespread; they are not restricted to cloud layers. The diurnal variation of gas and aqueous phase bromine was the opposite of that in cloud-free runs. Oxidation of S(IV) by HOBr and HOCl was important for cloud droplets, too. However, the relative importance of these oxidants changed compared to the cloud-free runs. Copyright 2002 by the American Geophysical Union.