Microbial Nitric Oxide, Nitrous Oxide, and Nitrous Acid Emissions from Drylands

Reactive nitrogen compounds (Nr, which include NOx (i.e., NO+NO2), N2O, ammonia, and HONO) have a large impact on atmospheric chemical composition and, thus, on climate. Nitric oxide (NO) is a chemically reactive trace gas that reacts with ozone (O3) to form NO2 (Crutzen 1979). The formation of O3 depends on a sensitive relationship between NOx (NO+NO2) and volatile organic compounds (VOC) (Sillman et al. 1990). Thus, even trace levels of NOx can activate O3 production. O3 itself can enrich the troposphere and as a short-lived climate pollutant (SLCP) can affect the climate (Shoemaker et al. 2013). Nitrous oxide (N2O) is among the most important greenhouse gases, together with H2O, CO2, and CH4. N2O has a relatively long lifetime, is enriched in the troposphere, and impacts the earth’s radiative balance (Ciais et al. 2013). When N2O enters the stratosphere, it reacts with O3 to NO, thereby depleting the ozone layer (Crutzen 1979)