Laboratory studies of free radical reactions in cloudwater.

摘要

Reactions in cloudwater can be important pathways for chemical transformation of atmospheric trace gases because of high solubility of reagent gases, rapid aqueous-phase kinetics, and large thermodynamic driving force. A key cloudwater reaction is oxidized of dissolved SO(sub 2) and H(sub 2)O(sub 2). It is thus important to understand processes controlling H(sub 2)O(sub 2) formation in the atmosphere by gas- and aqueous-phase reactions of HO(sub 2) free radicals. A concern with models of free radical chemistry in cloudwater is that of the applicability of present chemical kinetic schemes to such complex milieus. This concern arises because, at the low free-radical concentrations expected for cloudwater, reactions of radicals with trace impurities are favored over radical-radical reactions, which dominate at high radical concentrations commonly employed in laboratory investigations. We report initial results of a study in which the rate of change in H(sub 2)O(sub 2) concentration is monitored in synthetic and authentic cloudwater in which HO(sub 2) radicals are produced by (sup 60)Co(gamma) radiolysis at rates comparable to those expected upon transfer of HO(sub 2) from interstitial cloud air to cloudwater. These results indicate that micromolar concentrations of Fe(III) decrease H(sub 2)O(sub 2) yields and can even lead to H(sub 2)O(sub 2) loss rather than formation. Implications on cloud chemistry will be discussed. 14 refs., 2 figs.