Production of nitrogen oxides by a large spark generator

A large spark generator was used outdoors to determine the production of ni trogen oxides (NOx) from sparks with characteristics similar to those of li ghtning strokes. The experiment was conducted at the Rocket Triggered Light ning Program facility at Cape Canaveral, Florida, in August 1991, during th e Convection and Precipitation/Electrification field experiment. Plumes of NOx from spark generations were sensed by a NOx analyzer. The spark energy was 9.8 +/- 0.7 X 10(4) J, and the spark gap was 1.65 or 2.13 m. The plumes reached the analyzer inlet within 0.3-4.7 s after spark generation. The lq , concentrations varied, depending on the geometry of the plume. Laboratory studies of analyzer response permitted adjustment of the measured concentr ations to corrected concentrations. Production of NOx, in terms of mass of nitrogen, averaged 22.5 +/- 2.9 mg per spark, 11.7 +/- 1.5 mg m(-1) of spar k length, and 1.1 +/- 0.2 x 10(16) molecules J(-1). The median ratio of nit ric oxide (NO) to nitrogen dioxide (NOx) was 0.76, indicating substantial c onversion within a few seconds. Scaling of NO production to lightning energ y levels and dimensions yielded an annual global NOx production of 9.7 Tg y r(-1), similar to values estimated from recent thunderstorm measurements an d modeling studies. Recent satellite measurements suggest that cloud-to-gro und lightning flash frequency is an order of magnitude smaller than normall y assumed; estimates of global NOx production by lightning might also need to be reduced by an order of magnitude.