This study investigated the reactive dissolution of nitric oxide (NO) and nitrogen dioxide (NO2) mixtures in deionized water. The dissolution study was carried out in a flat surface type gas–liquid reaction chamber utilizing a gas flow-pattern resembling plasma jets which are often used in biomedical applications. The concentration of NO and NO2 in the gas mixtures was varied in a broad range by oxidizing up to 800 ppm of nitric oxide in Ar carrier gas with variable amount of ozone. The production of nitrite (NO2?) and nitrate (NO3?) in the water was proportional to treatment time up to 50 min. The concentration of NO3? was a power function of gas phase NO2 while the concentration of NO2? increased approximately linearly with gas phase NO2. The formation of NO2? and NO3? could be described by reactions between dissolved NO2 and NO in the water while the production rate was determined by diffusion-limited mass transport of nitrogen oxides to the bulk of the liquid. At higher NO2 concentrations, the formation of dinitrogen tetraoxide (N2O4) increased the formation rate of NO2? and NO3?. The identified mass transport limitation by diffusion suggests that convection of water created by the gas jet is insufficient and dissolution of nitrogen oxides can be increased by additional mixing. In respect of practical applications, the ratio of NO2? /NO3? in water could be varied from 0.8 to 5.3 with treatment time and gas phase NO2 and NO concentrations.
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