Human and animal wastes: Implications for atmospheric N2O and NOx

[1] More than 220 Tg N are processed annually through the global agriculture/animal/ human food chain. It is suggested that aerobic denitrification, reduction of nitrite formed in the first stage of nitrification, is an important source not only of global N2O but also of NOx. A simple top-down method indicates a globally averaged yield of 2% for N2O emitted as a consequence of human disturbances to the global nitrogen cycle. This yield can account not only for the contemporary budget of atmospheric N2O but also for trends observed over the past 1000 years. The associated microbial source of NOx is estimated assuming a NOx/N2O ratio of 3, consistent with results from a variety of laboratory and field studies. This source is significant, particularly for large developing countries such as China and India for which its contribution is comparable to that from fossil fuel.