Model investigations of atmospheric ammonia scavenging

In this study, a one-dimensional reactive storm model was used to calculate vertical concentration profiles of atmospheric ammonia and to examine the behavior of these concentrations during precipitation events. The model was initially used to generate clear-air profiles that were found to be consistent with those reported in the literature. A simple, convective storm was then applied to these initial profiles to determine the response of the gaseous ammonia concentrations to the precipitation event. The vertical ammonia concentrations were found to be significantly depleted by the storm event, with the maximum depletion occurring in the cloud layer. This alteration can have potentially significant effects in calculated reaction rates and in the upward flux of ammonia to the stratosphere. Several different storm conditions were tested, and all cases displayed the same characteristic depleted profiles. Calculations were performed for gaseous and aqueous ammonia only to assess the usefulness of this method for determining the depletion of highly soluble atmospheric gases and to specify the minimum amount of gaseous ammonia depletion occurring during a precipitation event. 17 refs., 7 figs., 1 tab.