Atmospheric Chemistry of H2O2, NO3, HONO, and HNO3: Influence of Aqueous Phase and Heterogeneous Processes

摘要

Aqueous phase and heterogeneous processes related to the production of H2SO4 and HNO3 in the atmosphere are investigated. The transformation of SO2 by gas phase reactions is slow, and aqueous reactions between dissolved SO2 and O3 or H2O2 are thought to account for much of the sulfate in precipitation. At the low pH values of cloud water and precipitation, only H2O2 reactions are viable. However, this reactant may be limited in the troposphere. Consequently, a direct O3-H2O source of H2O2 in the atmosphere is negligible. The conversion of nitrogen oxides, on the other hand, is slow in aqueous solution due to the low solubility of the HNO3 precursors at normal atmospheric conditions. Heterogeneous reactions between trace nitrogen oxides, NO3, N2O4, and N2O5, are possible and would result in a rapid generation of HNO3 in-cloud. A model sensitivity study is performed and demonstrates that under moderately polluted conditions these reactions are capable of producting nitrate at rates comparable to those observed in stratus clouds. This study also shows that heterogeneous processes are not necessary to resolve anomolous nocturnal measurements of NO3 and HONO. Additionally, a method is presented for calculating the solubilities of acid precursors and the acids themselves for use in future numerical predictions of cloud acidity and acid precipitation.