Calculation of sulfate and nitrate levels in a growing, reacting aerosol

Abstract

The temporal variation of particle size and chemical composition of a marine aerosol exposed to SO2, NH3, NO, NO2, H2SO4 and H2O vapor is studied to determine the effect of these parameters on the sulfate and nitrate levels in the particle. Results show that, for gas phase SO2 oxidation to sulfate, and liquid phase nitrate formation, those parameters that enhance sulfate formation tend to inhibit nitrate formation, and vice versa. Further, for the situation considered, the ratio predicted for sulfate and nitrate ions to ammonium ions is very nearly that found if all these ions were present in the form of NH4NO3 and (NH4)2SO4. This compares favorably with data on sulfate, nitrate and ammonium levels in the Los Angeles area. The model used is capable of representing a general growing, reacting aerosol; other cases studied by this approach are briefly outlined. Limitations of its use are discussed.