Nitric oxide production by simulated lightning: Dependence on current, energy, and pressure

The production of NO has been studied by means of arc discharges in the laboratory which simulate natural lightning in current waveform and amplitude (≃30 kA). Observations are compared to the results of a computational model that includes the dynamics of energy deposition and channel expansion, combined with the Zel'dovich equations to model the relevant chemical reactions. Results are expressed as NO produced per meter of arc length, and are measured as functions of dissipated energy and of peak current. It is found that at atmospheric pressure, the NO production per joule of dissipated energy is not constant. NO production per meter discharge length as a function of peak current appears to provide a more appropriate scaling factor for estimates of total global NO production. Production of NO2 was less than 10% of the production of NO, and by implication the production of O3 less still. From these data, and using published estimates of global lightning frequency, we derive an estimate of global NO production of 2.5 Tg(N)/yr for 30 flashes per second to 8.3 Tg(N)/yr for 100 flashes per second.