OH PHOTOCHEMISTRY AND METHANE SULFONIC-ACID FORMATION IN THE COASTAL ANTARCTIC BOUNDARY-LAYER

Studies of dimethylsulfide (DMS) oxidation chemistry were conducted at Palmer Station on Anvers Island, Antarctica, during the austral summe r of 1993/1994. Part of the study involved gas phase measurements of O H, methane sulfonic acid (MSA), and H2SO4 using a chemical ionization mass spectrometer, as well as measurements of the NO, CO, and O-3 conc entrations, Mean 24 hour concentrations from February 16-23 of OH, MSA , and H2SO4 were 1.1 x 10(5), 9.5 x 10(5), and 1.61 x 10(6) molecules cm(-3), respectively. Model calculations of OH compared well with obse rved levels (e.g., within 30%). The modeling results suggest that the dominant source of OH is from the reaction of O(D-1) with H2O, where O (D-1) is the product of O-3 photolysis, Because of the clean atmospher ic environment and predicted low nonmethyl hydrocarbon levels in Antar ctica, the dominant OH sink was found to be reaction with CO and CH4. Particulate levels of MSA were higher than could be attributed to cond ensation of boundary layer (BL) gas phase MSA on to the aerosol surfac e. Alternate mechanisms for generating MSA in the particle phase were speculated to involve either in-cloud oxidation of dimethylsulfoxide o r OH oxidation of DMS in the atmospheric buffer layer above the bounda ry layer followed by condensation of gas phase MSA on aerosols and tra nsport back to the BL [Davis et al., this issue].