| Abstract |
A general circulation model is used to provide three-dimensional global winds, vertical convective mass transport and precipitation fields for modeling the transport of reactive nitrogen and its removal by precipitation. Major sources of NOx include lightning, soil microbial activity, oxidation of N2O in the stratosphere and its transport to the troposphere, fossil-fuel combustion, and biomass burning. In the modeling study, a simplified approach for the atmospheric chemistry of NOx and its conversion to HNO3 is used. The gas-phase concentrations of NOx and HNO3 throughout the troposphere as well as the deposition of nitrate in precipitation and dry deposition are determined for January and July. Model predictions of NOx, HNO3, and NO3(-) concentrations in precipitation are compared to measured abundances as well as predictions of surface NOx and HNO3 concentrations. The model is used to treat three situations: only fossil-fuel sources, only natural sources, and all sources in order to discern the contribution of various sources to the observed and predicted abundances. Information about the source and deposition amounts are combined to create regional net nitrogen mass balances, thereby, illustrating which regions and sources contribute to increase nitrogen deposition. |
