Estimations of global no, emissions and their uncertainties

Abstract

The AERONOX programme investigated the impact of NO x emissions from aircraft on the atmosphere and included an extensive modelling programme. In the model comparisons undertaken within the AERONOX programme, a “standard” set of emissions of NO x from both aviation and non-aviation sources was required so that differences between the models could be examined. This paper describes the data sets used in the study. These were: fossil fuel combustion from stationary and mobile sources at Earth's surface (22 Tg N yr −1), tropical biomass burning (5 Tg N yr −1), soil microbial production of NO (4 Tg N yr −1), lightning (5 Tg N yr −1), and the stratospheric decomposition of nitrous oxide (0.6 Tg N yr −1), ). However, global emission inventories of trace gases are developing rapidly: this paper also presents some emission estimates updated since the AERONOX study and also attempts to quantify uncertainties. The lightning source was constructed using convective cloud-top height from a GCM and differential rates of NO production calculated for cloud-to-cloud, and cloud-to-ground strikes. A revised biomass inventory including deforestation, savanna burning, agricultural waste burning and biofuel combustion results in approximately 8 Tg Nyr −1. This estimate includes sources beyond the tropics. Both extrapolation of measurements of soil NO fluxes by biome type, and a further refinement of the AERONOX soils emission model resulted in an emission of approximately 7 Tg Nyr −1. Ammonia oxidation as a source of NO x is calculated to be 0.9 N Tg yr −1), with a range of 0-l.6 Tg N yr −1), which shows that this is a relatively unimportant source of NO x in the troposphere. Uncertainty estimates for all sources have been given and discussed. The global source term for NO x for all sources (including the revisions) is estimated to be 44 Tg N yr −1), with an uncertainty range of 23–81 Tg N yr −1), A future scenario for fossil fuel combustion is given for 2025 resulting in an emission term of 46.5 Tg N for this source, showing a pronounced shift in distribution to Asia and the Far-East.