Advances in understanding, models and parameterizations of biosphere-atmosphere ammonia exchange

Abstract

Ammonia (NH3) emission from the biosphere to the atmosphere is one of the many unintended consequences of reactive nitrogen (Nr) creation from inert dinitrogen gas (N2) through symbiotic biological nitrogen fixation (BNF) and the Haber-Bosch process, and of the agricultural usage of the fixed Nr for crop and meat production (Sutton et al. 2011). Conversely, NH3 emission is also one of the main precursors of the nitrogen cascade (Galloway et al. 2003), whereby the N atom of the NH3 molecule may potentially participate in a number of environmental impacts through a series of pathways and chemical and (micro-)biological transformations in the biosphere. As airborne NH3 is transported downwind from sources, chemically processed in the atmosphere, and dry- and wet-deposited to the Earth's surface, it may be converted in air, vegetation, soils and water successively to NH+4, NH-3, NO, N2O, many organic N forms, threatening in terms of air quality, water quality, soil quality, the greenhouse gas balance, ecosystems and biodiversity-5 key threats identified by Sutton et al. (2011).