DETERMINATION OF THE DRY DEPOSITION FLUX OF SO2 USING COSMOGENIC S-35AND BE-7 MEASUREMENTS

The radionuclides S-35 (half-life = 87 days) and Be-7 (half-life = 53 days) are produced in the atmosphere by cosmic rays. The former quickl y becomes gaseous (SO2)-S-35 while Be-7 is directly associated with ae rosols. The production rates of both nuclides increase virtually expon entially with increasing altitude. Conversion of (SO2)-S-35 to particu late (SO4)-S-35 is effected by oxidation after which, like Be-7, it is subject to removal by precipitation in the troposphere. The (SO2)-S-3 5 is also removed from the gaseous state by solution and oxidation in water droplets (clouds) and, at the planetary surface, through ''dry d eposition'' (i.e., oxidation on plant and other surfaces). The kinetic s controlling removal df (SO2)-S-35 also operate on SO2 in the atmosph ere from natural and pollution sources. Through measurements of (SO2)- S-35, (SO4)-S-35, Be-7, SO2 and SO4 in air samples in the boundary lay er and the wet precipitation fluxes of the (SO4)-S-35, Be-7, and SO4 i ntegrated over monthly intervals, we have established the following pa rameters at New Haven, Connecticut for 1992. Based on the Be-7 balance the average effective height of the troposphere, H-t, varies from 13 ion for me winter months to 17 through 21 km for the spring and summer months. The height of the surface reactive ''boundary'' layer, H-b, i s about 0.5 ion for all but the month of August. By optimization proce dures, best solutions were obtained for scavenging coefficients for bo th the free troposphere and the surface reactive layer together with t he dry deposition coefficient and the mean residence time of air in th e surface reactive layer. The highest fraction of dry deposition flux to total S flux occurred in the fall and winter. The weighted average for the entire year is 0.25.