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 summer of 1993/1994. Part of the study involved gas phase measurements of OH, methane sulfonic acid (MSA), and H 2 SO 4 using a chemical ionization mass spectrometer, as well as measurements of the NO, CO, and O 3 concentrations. Mean 24 hour concentrations from February 16–23 of OH, MSA, and H 2 SO 4 were 1.1 × 10 5 , 9.5 × 10 5 , and 1.61 × 10 6 molecules cm −3 , respectively. Model calculations of OH compared well with observed levels (e.g., within 30%). The modeling results suggest that the dominant source of OH is from the reaction of O( 1 D ) with H 2 O, where O( 1 D ) is the product of O 3 photolysis. Because of the clean atmospheric environment and predicted low nonmethyl hydrocarbon levels in Antarctica, the dominant OH sink was found to be reaction with CO and CH 4 . Particulate levels of MSA were higher than could be attributed to condensation of boundary layer (BL) gas phase MSA on to the aerosol surface. Alternate mechanisms for generating MSA in the particle phase were speculated to involve either in‐cloud oxidation of dimethylsulfoxide or OH oxidation of DMS in the atmospheric buffer layer above the boundary layer followed by condensation of gas phase MSA on aerosols and transport back to the BL [ Davis et al. , this issue].