Nitrogen oxides emissions from lightning: Global source rate and tropical/mid-latitude differences

Kurzfassung

Lightning-induced nitrogen oxides (LNOx) have several important implications for atmospheric chemistry and climate. The global LNOx source is one of the largest natural sources of NOx in the atmosphere and certainly the largest source of NOx in the upper troposphere, in particular in the tropics. The LNOx source rate has been often cited to be the least known one within the total atmospheric NOx budget. Considerable progress has been made recently which allows reducing the uncertainty of the global LNOx value. This includes ground-based and satellite observations of various lightning signals, satellite observations of NO2 column and profile distributions, airborne in-situ measurements of NOx abundance near thunderstorms at midlatitudes and over tropical continents, where most lightning occurs, detailed cloud-resolving model studies, and improved global models. This paper reviews the present knowledge on the global LNOx source rate and its still large uncertainties (Schumann and Huntrieser, ACP, 2007). Mainly as a result of global model studies for various LNOx parameterisations tested with related observations, the best estimate of the annual global LNOx nitrogen mass source and its uncertainty range is (5+-3) Tg/a in this study. Some recent findings from analysis of field experiments comparing LNOx efficiency of mid-latitude and tropical thunderstorms are also reported.