DMS OXIDATION IN THE ANTARCTIC MARINE BOUNDARY-LAYER - COMPARISON OF MODEL SIMULATIONS AND FIELD OBSERVATIONS OF DMS, DMSO, DMSO2, H2SO4(G), MSA(G), AND MSA(P)

A sulfur field study (SCATE) at Palmer Station Antarctica (January 18 to February 25) has revealed several major new findings concerning (di methyl sulfide) DMS oxidation chemistry and the cycling of sulfur with in the Antarctic environment. Significant evidence was found supportin g the notion that the OH/DMS addition reaction is a major source of di methyl sulfoxide (DMSO), Methane sulfonic acid (MSA(g)) levels were al so found to be consistent with an OH/DMS addition mechanism involving the sequential oxidation of the products DMSO and methane sulfinic aci d (MSIA). Evidence supporting the hypothesis that the OH/DMS addition reaction, as well as follow-on reactions involving OH/DMSO, are a majo r source of SO2 was significant, but not conclusive. No evidence could be found supporting the notion that reactive intermediates (i.e., SO3 ) other than SO2 were an important source of H2SO4. Quite clearly, one of the major findings of SCATE was the recognition that a large fract ion of the Antarctic oxidative cycle for DMS (near Palmer Station) too k place above the boundary layer (BL) in what we have labeled here as the atmospheric buffer layer (BuL). Although still speculative in plac es, the overall picture emerging from the SCATE field/modeling results is one involving major coupling between chemistry and dynamics in the Antarctic. At Palmer the evidence points to frequent episodes of rapi d vertical transport from a very shallow marine BL into the overlying BuL. Due to the combination of a long photochemical lifetime for DMS a nd the frequency of shallow convective events, a large fraction of oce an released DMS is transported into the BuL while still in its unoxidi zed state. There, in the presence of elevated OH and low aerosol scave nging, high levels of oxidized sulfur accumulate. Parcels of this BuL air are then episodically entrained back into the BL, thereby providin g a controlling influence on BL SO2, DMSO, and DMSO2. Additionally, be cause SO? and DMSO are major precursors to H2SO4 and MSA, BuL chemistr y, in conjunction with vertical transport, also act to control BL leve ls of the latter species. Although many uncertainties remain in our un derstanding of Antarctic DMS chemistry, the above picture already sugg ests that previous chemical interpretations of Antarctic field data ma y need to be altered.