ESTIMATIONS OF GLOBAL NOX EMISSIONS AND THEIR UNCERTAINTIES

zThe AERONOX programme investigated the impact of NOx emissions from a ircraft on the atmosphere and included an extensive modelling programm e. In the model comparisons undertaken within the AERONOX programme, a ''standard'' set of emissions of NOx from both aviation and non-aviat ion sources was required so that differences between the models could be examined. This paper describes the data sets used in the study. The se 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 T g N yr(-1)). However, global emission inventories of trace gases are d eveloping rapidly: this paper also presents some emission estimates up dated since the AERONOX study and also attempts to quantify uncertaint ies. The lightning source was constructed using convective cloud-top h eight from a GCM and differential rates of NO production calculated fo r cloud-to-cloud, and cloud-to-ground strikes. A revised biomass inven tory including deforestation, savanna burning, agricultural waste burn ing and biofuel combustion results in approximately 8 Tg N yr(-1) This estimate includes sources beyond the tropics. Both extrapolation of m easurements of soil NO fluxes by biome type, and a further refinement of the AERONOX soils emission model resulted in an emission of approxi mately 7 Tg N yr(-1). Ammonia oxidation as a source of NOx is calculat ed to be 0.9 N Tg yr(-1) with a range of 0-1.6 Tg N yr(-1), which show s that this is a relatively unimportant source of NOx in the troposphe re. Uncertainty estimates for all sources have been given and discusse d. The global source term for NOx for all sources (including the revis ions)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. ( C) 1997 Published by Elsevier Science Ltd.