The tropospheric gas-phase degradation of NH3 and its impact on the formation of N2O and NOx

The gas-phase degradation of NH3 in the atmosphere still has many uncertain ties. One of them is the possible isomerisation of NH2O to NHOH, as indicat ed by kinetic studies. Since NH2O is formed during the gas-phase oxidation of ammonia in the troposphere, this reaction can potentially influence the subsequent production of N2O and NOx. So far, the isomerisation has never b een implemented into current chemical schemes describing the atmospheric ga s-phase degradation of NH3 and its atmospheric relevance has never been ass essed. The N2O yield from NH3 degradation is calculated to be in the range of 10-43 %. It depends on the NO2 and O-3 concentrations, but is independen t of the NH3 concentration. Compared with the results from recent literatur e, the N2O yield derived from the new mechanism is 20-80% lower, implying a smaller global N2O source strength of 0.4 Tg yr(-1). The production of NH2 SO2 seems to be less important for the atmospheric degradation of NH3.NH3 o xidation is a sink for NOx at NOx mixing ratios of more than about 1 ppb an d a source at lower NOx burdens.