Lightning‐produced NO x (LINOX): Experimental design and case study results

This paper investigates the role of lightning in the production of nitrogen oxides (NO x ) and their subsequent distribution by thunderstorms. These questions were addressed by the field experiment LINOX (lightning produced NO x ), which was performed in southern Germany in July 1996. The structure of thunderstorms was observed by radar and satellite, the lightning activity was recorded by a lightning detection network, and airborne chemical measurements were performed aboard a jet aircraft penetrating the storm anvils. NO x 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 NO x was found to be dominant in narrow peaks produced by flashes as well as near cloud boundaries, probably because of increased photolysis rates of NO 2 . Using CO 2 as an air mass tracer, the lightning‐produced NO x amount was discriminated 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‐produced NO x was present in the same order of magnitude as the amount of NO x originating from lower levels; during later stages of cloud development, the content of the former even exceeded the latter one. A simple two‐dimensional model of advection and dispersion of the lightning‐produced NO x was able to reproduce the general structure of the anvil NO x plume. Some NO x peaks could directly be attributed to flash observations close to the aircraft track.