Exchange of gaseous nitrogen compounds between agricultural systems and the atmosphere

Crop and livestock agricultural production systems are important contributors to local, regional and global budgets of NH₃, NO_x (NO + NO₂) and N₂O. Emissions of NH₃ and NO_x (which are biologically and chemically active) into the atmosphere serve to redistribute fixed N to localand regional aquatic and terrestrial ecosystems that may otherwise be disconnected from the sources of the N gases. The emissions of NO_x also contribute to local elevated ozone concentrations while N₂O emissions contribute to global greenhouse gas accumulation and to stratospheric ozone depletion. Ammonia is the major gaseous base in the atmosphere and serves to neutralize about 30% of the hydrogen ions in the atmosphere. Fifty to 75% of the [ap] 55 Tg N yr^-1 NH₃ from terrestrial systems is emitted from animal and crop-based agriculture from animal excreta and syntheticfertilizer application. About half of the 50 Tg N yr^-1 ofNO_x emitted from the earth surface annually arises from fossil fuel combustion and the remainder from biomass burning and emissions from soil. The NO_x emitted, principally as nitric oxide (NO), reacts rapidly in the atmosphere and in a complex cycle with light, ozone and hydrocarbons, and produces nitric acid and particulate nitrate. These materials can interact with plants and the soil locally or be transported form the site and interact with atmospheric particulate to form aerosols. These salts and aerosols return to fertilize terrestrial and aquatic systems in wet and dry deposition. A small fraction of this N may be biologically converted to N₂O. About 5% of the total atmospheric greenhouse effect is attributed to N₂O from which 70% of the annual global anthropogenic emissions come from animal and crop production. The coupling of increased population with a move of a large sector of the world population to [ABSTRACT FROM AUTHOR]