Production of nitrogen oxides by a large spark generator

A large spark generator was used outdoors to determine the production of nitrogen oxides (NO x ) from sparks with characteristics similar to those of lightning strokes. The experiment was conducted at the Rocket Triggered Lightning Program facility at Cape Canaveral, Florida, in August 1991, during the Convection and Precipitation/Electrification field experiment. Plumes of NO x from spark generations were sensed by a NO x analyzer. The spark energy was 9.8±0.7×10 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 NO x concentrations varied, depending on the geometry of the plume. Laboratory studies of analyzer response permitted adjustment of the measured concentrations to corrected concentrations. Production of NO x , in terms of mass of nitrogen, averaged 22.5±2.9 mg per spark, 11.7±1.5 mg m −1 of spark length, and 1.1±0.2×10 16 molecules J −1 . The median ratio of nitric oxide (NO) to nitrogen dioxide (NO 2 ) was 0.76, indicating substantial conversion within a few seconds. Scaling of NO x production to lightning energy levels and dimensions yielded an annual global NO x production of 9.7 Tg yr −1 , similar to values estimated from recent thunderstorm measurements and modeling studies. Recent satellite measurements suggest that cloud‐to ground lightning flash frequency is an order of magnitude smaller than normally assumed; estimates of global NO x production by lightning might also need to be reduced by an order of magnitude.