Light-induced formation of hydroxyl radicals in fog waters determined by an authentic fog constituent, hydroxymethanesulfonate.

The determination of the photo-production rate of hydroxyl radical (OH) in atmospheric liquids is of fundamental importance to an understanding of atmospheric aquatic chemistry. Recently, several studies have been performed to examine the photo-chemical formation rate of OH in cloud and fog waters using a free radical quenching technique with addition of a relatively large concentration of organic compounds as an OH scavenger. The addition of free-radical scavenger chemicals may significantly alter the nature of the sample water and its OH production rate. In this paper, an authentic constituent, hydroxymethanesulfonate, is proposed as a free radical probe for the measurement of photo-chemical generation rate of OH in fog water. At 313 nm, an apparent quantum yield for the production of OH in a fog water was found to be 0.012+/-0.001, indicating that aqueous-phase photo-chemical processes could represent a significant and may be a dominant source of OH in atmospheric liquids.