THE RESPONSE OF SULFATE LINEARITY AND PRECIPITATION CHEMISTRY TO GAS-PHASE PROFILES

Results are reported from a series of cloud chemistry simulations designed to evaluate the sensitivity of precipitation sulfate concentrations to changes in the shape and mass of the preexisting gas phase profiles. Linearity factors relating chemical inflow conditions to deposition are evaluated. The height from which any given fraction of the sulfur in precipitation came in stratiform storms was found to be approximately equal to the height at which the corresponding fraction of initial sulfur was located. This source height was greater for convective storms. Changes in the total sulfur generally resulted in an almost proportional change in the resulting precipitation sulfate concentrations. Because stratiform storms rely more strongly on the initial gas-phase profiles to define the available oxidant at a given height, the deposition and SO2 linearity factors associated with such storms were found to be more sensitive to the initial height dependence of the ratio [SO2] and [H2O2] than was found for convective storms. The deposition and the linearity factors for convective storms were found to be more strongly dependent on the total column mass of these species. The precipitation sulfate concentration and linearity were found to be generally insensitive to perturbations in the fine structure of the initial gas-phase profiles.