Abstract. The production of NO has been studied by means of arc discharges in the laboratory which simulate natural lightning in current waveform and amplitude (___ 30kA). 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

Abstract. The first global tropospheric forecasts of O3 and its precursors have been used in the daily flight planning of field measurement campaigns. The 3-D chemistry-transport model MATCH-MPIC is driven by meteorological data from a weather center (NCEP) to produce daily 3-day forecasts of the global distributions of O3 and related gases, as well as regional CO tracers. This paper describes the forecast system and its use in three field campaigns, MINOS, CONTRACE and INDOEX. An overview is given of the forecasts by MATCH-MPIC and by three other chemical weather forecast models (EURAD, ECHAM, and FLEXPART), focusing on O3 and CO. Total CO and regional CO tracers were found to be the most valuable gases for flight planning, due to their relatively well-defined anthropogenic source regions and lifetimes of one to a few months. CO was in good agreement with the observations on nearly all the flights (generally  r > 0.7, and the relative RMS differences for the deviations from the means was less than 20%). In every case in which the chemical weather forecasts were primarily responsible for the flight plans, the targeted features were observed. Three forecasted phenomena are discussed in detail: outflow from Asia observed in the Mediterranean upper troposphere during MINOS, outflow from North America observed in the middle troposphere over northern Europe during CONTRACE, and the location of the "chemical ITCZ'' over the Indian Ocean during INDOEX. In particular it is shown that although intercontinental pollution plumes such as those observed during MINOS and CONTRACE occur repeatedly during the months around the campaigns, their frequency is sufficiently low (~10--30% of the time) that global chemical weather forecasts are important for enabling them to be observed during limited-duration field campaigns. The MATCH-MPIC chemical weather forecasts, including an interface for making customized figures from the output, are available for community use via http://www.mpch-mainz.mpg.de/~lawrence/forecasts.html.

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We have investigated NO production in the expansion phase of a lightning discharge using a hydrodynamic model coupled with the chemical rate equations for the two Zel'dovich reactions and oxygen dissociation. We have found that most of the NO production occurs early in the discharge, prior to shock wave formation, and that the rapid drop in density, not temperature, controls NO formation. The number of mo!eeu!es per Joule (P) depends strongly on the energy per unit 3olume in the initial heated channel: this dependence is nonlinear with a maximum value of 26 x 10 •e molecules NO/J. For a representative discharge at a pressure of I arm, the number produced is 15 x 10'6/I. Initial investigation indicates that for a constant energy density (estimated to be about 6 Ml/m •) the rate of production drops off rapidly with decreasing air density and thus altitude. Use of P appropriate for sea level pressure may !cad to a major overestimate of the rate of NO formation in atmospheric lightning, much of which occurs at high altitude. We present suggestions for new laboratory experiments to quantify global NO production by lightning.

Nitrogen oxides have been shown to catalyze the destruction of stratospheric ozone. Previous estimates of nitric oxide emissions from high‐altitude aircraft have taken into account engine emissions only. This study was undertaken to determine whether nitric oxide production in the hot viscous boundary layer surrounding the skin of a hypersonic aircraft can significantly increase estimates of total NO emissions. The described model approximates the viscous boundary layer as a series of finite stream tubes with time‐dependent and temperature‐dependent chemical kinetics and mass flow rates. Nitric oxide equilibrium mole fraction for air peaks at ≅ 3700 K. At hypersonic speeds the viscous effects near the aircraft skin will induce these very high temperatures. Along the skin surface of a 60 m craft, the NO mole fraction can be locally as high as 0.044. Nitric oxide output from this thin boundary layer becomes significant when integrated over the entire trailing edge of the aircraft. This model predicts that nitric oxide production in the boundary layer should be taken into account at speeds above Mach 8. Above Mach 8, boundary layer volume and temperature increase rapidly. At stratospheric speeds approaching Mach 16, the nitric oxide production in the boundary layer increases to the point where it roughly equals the nitric oxide output from the engines. Above Mach 16, the boundary layer produces the majority of the NO emissions. This additional source of nitric oxide will play an ever‐increasing role as aircraft fly at higher speeds and altitudes. Significant errors in total NO emission estimates will result if the viscous boundary layer is not taken into account at speeds above Mach 8.