Lightning-produced NOx (LINOX): Experimental design and case study results

This paper investigates the role of lightning in the production of nitrogen oxides (NOx) and their subsequent distribution by thunderstorms. These que stions were addressed by the field experiment LINOX (lightning produced NOx ), which was performed in southern Germany in July 1996. The structure of t hunderstorms was observed by radar and satellite, the lightning activity wa s recorded by a lightning detection network, and airborne chemical measurem ents were performed aboard a jet aircraft penetrating the storm anvils. NOx concentrations in the storm anvils were found to typically range from 1 to 4 parts per billion by volume. The NO contribution to the total NOx was fo und to be dominant in narrow peaks produced by flashes as well as near clou d boundaries, probably because of increased photolysis rates of NO2. Using CO2 as an air mass tracer, the lightning-produced NOx amount was discrimina ted from the contribution due to transport of air from the boundary layer. It was found from a case study of a large storm anvil that lightning-produc ed NOx was present in the same order of magnitude as the amount of NOx orig inating from lower levels; during later stages of cloud development, the co ntent of the former even exceeded the latter one. A simple two-dimensional model of advection and dispersion of the lightning-produced NOx was able to reproduce the general structure of the anvil NOx plume. Some NOx peaks cou ld directly be attributed to flash observations close to the aircraft track .