A large spark generator was used outdoors to determine the production of nitrogen oxides (NOx) 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 NOx from spark generations were sensed by a NOx analyzer. The spark energy was 9.8±0.7×104 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 NOx 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 NOx, 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±0.2×1016 molecules J−1. The median ratio of nitric oxide (NO) to nitrogen dioxide (NO2) was 0.76, indicating substantial conversion within a few seconds. Scaling of NOx production to lightning energy levels and dimensions yielded an annual global NOx 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 NOx production by lightning might also need to be reduced by an order of magnitude.
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