A theoretical explanation is presented for the recent observation of a maximum in the production of NO2 in onset streamers in (positive) point-to-plane gaps in air at atmospheric pressure. The observed NO2 yield was an order of magnitude higher than in the steady corona obtained by increasing the gap voltage. In the exemplary case considered, the gap voltage was 7.0 kV, the mean current 1.43 mu A, the average time between consecutive streamers 0.64 ms, the height of the streamers 9.5 mm, the loss of energy about 390 eV/molecule and the yield of NO2 was 1.0*1011 molecules per streamer. According to the proposed model, the NO synthesis occurs mainly via the oxidation of vibrationally excited N2. The small diameter of streamers and the diffusion are crucial in the suppression of reverse reactions. The theoretical results are sensitive to uncertainties in input data, for example, in the cross sections for vibrational excitation and for electron-ion recombination. The analytical method with closed-form expressions was adequate for the calculations. An auxiliary series of experiments aimed at maximising the ozone yield; the least expenditure of energy was 42 eV per ozone molecule.

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A method is presented that yields exact closed-form solutions in curvilinear coordinates for the partial differential equations determining the electric field in a stationary flow of unipolar ions with constant mobility. The method is applied to the parabolic cylindrical, elliptic cylindrical, bipolar, parabolic, and spheroidal coordinates. The new solutions approach infinity roughly in the manner of the classical parallel-plate solution. They are expected to apply to analyses of non-self-sustained ion flows.