Nitrogen Emissions from Soils

The oxidized nitrogen species nitric oxide (NO), nitrogen dioxide (NO₂) and nitrous oxide (N₂O) play an important role in tropospheric and stratospheric chemistry. NO and NO₂, collectively known as NO_x, regulate the tropospheric photochemical production of ozone and the abundance of the hydroxyl radical (OH, the main oxidant of the atmosphere), whereas N₂O influences stratospheric ozone chemistry (Crutzen, 1974). Moreover, N₂O is a long-lived greenhouse gas. The reduced nitrogen species ammonia (NH₃) is involved in rain and cloud water chemistry, aerosol formation, it acidifies ecosystems (e.g. van Breemen et al., 1982) and plays a crucial role in the tropospheric sulphur cycle (e.g. Bouwman et al., 1997). Nitrogen species are also relevant for the biogeochemical cycling of terrestrial nutrients, e.g. by regulating the Net Primary Production (NPP) in a future carbon dioxide-enhanced climate (Holland et al., 1997). A large input of nitrogen via wet and dry deposition can also result in forest decline as a consequence of nitrogen saturation or acidification of the soil (Bouwman et al., 1997)