Nitrogen oxides are nowadays a subject of global concern. Several types of nitrogen oxides exist in the environment: N2O, NO, NO2, N2O3, N2O4, N2O5. The abbreviation NOx usually relates to nitric oxide NO, nitrogen dioxide NO2, and nitrous oxide N2O. The first two are harmful pollutants for both environment and human health, whereas the third is one of the greenhouse gases. Implementation of stringent NOx emission regulations requires the development of new NOx removal technologies from exhaust gases. One of many proposals for NOx emission reduction is the application of an oxidizing agent which would transform NOx to higher nitrogen oxides with higher solubility in water. The main objective of the paper was to present the rate constant of nitric oxide oxidation, determined in our studies.