Studies of the gas-phase reaction of water vapor and parts-per-million concentrations of nitrogen dioxide were made at atmospheric pressure and near ambient temperatures. Of special interest in the work was careful chemical analysis-water to values less than 2 ppm and nitric oxide and nitrogen dioxide to values less than 5 ppm-and absence of mist. The initial rate of disappearance of nitrogen dioxide was first order with respect to water and second order with respect to nitrogen dioxide. Nitric oxide and nitric acid were the principal products. A third-order rate constant of 5.50 (±0.29) X 104 I.2 mol-2 sec"1 was found at 25°C. Results of the work are applicable to air pollution studies and to the understanding of the mechanism for the absorption of nitrogen dioxide into aqueous solution.

A study was made of the kinetics of the oxidation of nitric oxide in the presence of water in the temperature region of 25-50°C. The kinetics of the actual oxidation of the nitric oxide in the presence of water vapor were not different from those of the dry oxidation. That is three principle reactions were believed to occur: 2ND + 02 = 2N02 (reaction A); NO + N02 + H20 = 2HN02 (reaction B); 3HN02 + K20 = NO + 2HNO3, (reaction C). For the condition studied, reaction C occurred only to a small extent. Of significant importance is that water significantly catalyzes the oxidation of nitric oxide on a Car bow ax 5000 surface, which suggests that oxidation of nitric oxide must be studied under very carefully controlled conditions.

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