Hydrogen peroxide and sulfur (IV) in Los Angeles cloud water

Airborne collection and chemical analysis of cloud water samples in the Los Angeles Basin showed that the reaction between hydrogen peroxide and sulfur (IV) was inhibited in the collected samples, so these species reacted to form sulfate more slowly in these samples than would be expected from published laboratory data. The cloud water contained formaldehyde, which can react with sulfite to form hydroxymethanesulfonic acid (HMSA). This adduct contributed to measured S(IV) concentrations in the cloud water, which were more than 100 times greater than those calculated from ambient sulfur dioxide concentrations, water pH, and the Henry's Law and acid-base equilibrium constants. The average S(IV) concentration constituted 14% of the sulfate determined in the cloud water after oxidation. It is likely that a salt formed from HMSA contributed to prior observations of S(IV) and volatile sulfur in the Los Angeles aerosol.