Cloud Chemistry Studies at the Whiteface Mountain Field Station

Measurements of gas phase concentrations of SO(,2), sulfate, NO(,x), nitric acid and nitrate and aqueous phase cloud chemistry measurements made at the summit of Whiteface Mountain during the summer of 1982 were used to investigate the aqueous-phase oxidation of SO(,2) in cloud water. Previous studies of cloud water chemistry and aqueous oxidation of SO(,2) are reviewed and the chemical climatology of Whiteface Mountain and the surrounding region are discussed. The Air Resources Laboratories Advanced Trajectory and Dispersion Mode ARL-ATAD trajectories were used to study the atmospheric concentrations and cloud water concentrations of the various chemical constituents. Highest concentrations of most substances were observed in air that approach Whiteface from the southwest reflecting the higher emission densities of these substances in that direction. Ratios of acidity to the primary ions associated with that acidity, nitrate and sulfate, were used to compare the chemistry of cloud-free and cloudy air. It was determined that the acidity of cloud water can best be explained by assuming that SO(,2) is oxidized to sulfuric acid in cloud water. SO(,2) concentrations were observed to fall to below the detectable limit of 0.3 ppb during most period of cloudiness at the summit. Two cases were studied in detail. One, a cap cloud, showed rapid decrease of SO(,2) concentrations to their previous levels as the cloud dissipated. The other case showed SO(,2) concentrations at relatively high levels during the beginning of a cloud event. It was concluded that aqueous oxidation of SO(,2) is a common occurrence in the clouds studied, but there are some periods when all the SO(,2) is not oxidized.