Time: 15:00PM, Oct.14,  2011

Abstract:

Dimethyl sulfide (CH₃SCH₃, DMS) is produced by phytoplankton in seawater. Emission of oceanic DMS to the atmosphere is thought to be second only to anthropogenic SO₂ as a global source of atmospheric sulfur. It has been suggested that processes resulting from cycling of DMS through the ocean-atmosphere system may regulate climate on a global cycle.The same microorganisms that produce DMS also produce dimethyl selenide (CH₃SeCH₃, DMSe), albeit at levels approximately four orders of magnitude smaller than those of DMS. Oceanic emission is thought to be the single largest source of atmospheric DMSe, and atmospheric transport, transformation, and subsequent deposition are thought to be key processes influencing selenium levels and speciation in terrestrial environments. Serious health effects are associated with both insufficient and excess selenium in animals, including humans. Developing a quantitative description of the atmospheric chemistry of DMS and DMSe is necessary for understanding the climate and health effects described above. 

In this presentation, the current level of understanding of the atmospheric chemistries of DMS and DMSe will be reviewed and new laboratory results will be presented that improve our understanding of the reactions of atomic chlorine, an important oxidant in the marine boundary layer, with DMS and DMSe. The laboratory results quantify the rate coefficients for H-abstraction and addition and also represent the first experimental determination of X−Cl (X=S or Se) bond strengths in the 2-center−3-electron bonded adducts that may be important intermediates in the Cl-initiated atmospheric oxidations of DMS and DMSe. 

Contact: Prof.MU Yujing, Tel.: 62849125, Email：yujingmu@rcees.ac.cn