Measurements of Sulfuric Acid and Methanesulfonic Acid During ISCAT 2000

Gas phase sulfuric and methanesulfonic acid (MSA) were measured at the South Pole using a selected ion chemical ionization mass spectrometric technique during ISCAT 2000. Both compounds were typically quite low. Upon only a few occasions did sulfuric acid increase briefly into the 1x10⁶ molecules cm^-3 range and MSA increase into the mid 10⁵ molecules cm^-3 range. While MSA was typically close to its detection limit at about 1x10⁵ molecules cm^-3, sulfuric acid was typically only a few times higher at 2 or 3x10⁵ molecules cm^-3. Despite the consistently high OH concentrations measured at this site, the low observed gas phase sulfuric acid suggests that average local sulfur dioxide concentrations are probably fairly low. Methanesulfonic acid remained low throughout the campaign, also suggesting that DMS was probably not being oxidized locally. Thus, the MS observed in aerosols is believed to have been transported in the particle phase from areas closer to the coast.