Atmospheric Chemistry of Hydrogen Peroxide, Nitrogen-Trioxide, Nitrous Acid, and Nitric Acid: Influence of Aqueous Phase and Heterogeneous Processes.

Abstract

Aqueous phase and heterogeneous processes related to the production of H(,2)SO(,4) and HNO(,3) in the atmosphere are investigated. The transformation of SO(,2) by gas phase reactions is slow, and aqueous reactions between dissolved SO(,2) and O(,3) or H(,2)O(,2) are thought to account for much of the sulfate in precipitation. At the low pH values of cloud water and precipitation, only H(,2)O(,2) reactions are viable. However, this reactant may be limited in the troposphere. Measurements of H(,2)O(,2) vapor using aqueous collection are shown to suffer from artifact formation and suggest that O(,3) and H(,2)O reactions could produce H(,2)O(,2) in cloud and precipitation. Experiments to illucidate the O(,3), H(,2)O, and H(,2)O(,2) mechanism show that under pure conditions this process is the result of surface reactions on the glass collector walls. Consequently, a direct O(,4)-H(,2)O source of H(,2)O(,2) in the atmosphere is negligible. The conversion of nitrogen oxides, on the other h and , is slow in aqueous solution due to the low solubility of the HNO(,3) precursors at normal atmospheric conditions. Heterogeneous reactions between trace nitrogen oxides, NO(,3), N(,2)O(,4), and N(,2)O(,5), are possible and would result in a rapid generation of HNO(,3) in-cloud. A model sensitivity study is performed and demonstrates that under moderately polluted conditions these reactions are capable of producing nitrate at rates comparable to those observed in stratus clouds. This study also shows that heterogeneous processes are not necessary to resolve anomalous nocturnal measurements of NO(,3) 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.