NOx Emissions from Aircraft. Effects of lightning and convection on changes in tropospheric ozone

摘要

In this report, a global 3-dimensional chemical tracer model is used to study the impact of uncertainties in lightning emissions of NOx and deep convection activity on the changes in tropospheric ozone due to NOx emissions from subsonic aircraft. Three sets of two chemical tracer model experiments were performed, with and without emissions from aircraft: a reference set with normal convection and 12 Tg(N)/yr from lightning, a set with reduced lightning source 5 Tg(N)/yr and one set with reduced convective activity. A zonally homogeneous increase in upper tropospheric ozone north of 40(sup o)N, reaching 5-6 ppbv during May, was found in the reference case. Reduced emissions from lightning lead to 50-70% higher enhancement of ozone at northern mid-latitudes during summer because of lower background concentrations of NOx and more efficient ozone production. Reduced convective mixing lead to a 40% increased enhancement in aircraft-induced ozone at northern mid-latitudes and 150% in the tropics. In this case background NOx levels were higher in the upper troposphere, but the decreased ozone production efficiency was compensated by decreased downward mixing of ozone produced by emissions from aircraft. 55 refs., 8 figs., 4 tabs.