Identification of Hydroxymethanesulfonate in Fog Water

Abstract

Previous studies have suggested that hydroxymethanesulfonate ion (HMSA) can be an important species in fog and cloud water. Formation of HMSA explains observed excesses of sulfur in the S(IV) state (+4 oxidation state) and formaldehyde (CH_2O) in fogs and clouds. HMSA was determined in fog water by a novel ion-pairing chromatographic technique. Concentrations in samples collected in Bakersfield, California, within 5 kilometers of major sources of sulfur dioxide (SO_2), were as high as 300 micromoles per liter. Total CH_2O and S(IV) concentrations, which were measured independently, ranged from 10 to 200 and 5 to more than 300 micromoles per liter, respectively. Concentrations of CH_2O, S(IV), and HMSA at Buttonwillow, California, which is 15 kilometers from the nearest source of SO_2, were less than those at Bakersfield but not absent. These data confirm that HMSA forms in atmospheric water droplets and can reach appreciable concentrations. HMSA represents an important source of acidity for water droplets and may also play a role in long-distance transport and transformation of SO_2.