HOMOGENEOUS OXIDATION OF SULFUR-DIOXIDE IN CLOUD DROPLETS

In light of recent criticism as to the importance of the uncatalyzed oxidation of aqueous SO2 by dissolved oxygen, a reassessment of pertinent cloud water measurements has been undertaken. These measurements have been compared with predictions from the Easter and Hobbs (1974) interactive cloud-chemistry model after the model was updated with respect to both ambient trace gas inputs and the dissolved SO2 oxidation rate law employed. The model was further modified to output both the mean cloud water pH and the pH of individual droplet size classes as a function of time. The sensitivity of the sulfate production predicted by the model to the initial cloud condensation nucleus spectrum and cloud interaction time was also investigated. The modeling results show that the Easter-Hobbs model predicts cloud water pH's in accord with measurements and that at these pH's the uncatalyzed oxidation of aqueous SO2 by dissolved oxygen produces significant amounts of sulfate. © 1979.