The role of nitrogen oxides in the tropospheric photochemical system is re‐evaluated in the light of recent measurements of the rate constants for two key reactions. A model for nitrogen oxides is discussed which yields surface NOx(NO+NO2) levels approaching 1 ppb in NOxsource regions but less than 0.1 ppb outside source regions. Applying the new rate coefficients implies increased radical concentrations and a more intense O3and CO photochemistry. Even for densities of 0.1 ppb or less, NOxstill leads to significant local O3production and conversion of HO2to OH. Unrealistic O3profiles are obtained with the new rate coefficients for surface NOxdensities of about 1 ppb, while reasonable agreement with observation is obtained with lower NOxdensities. Feedback processes between CO, NOx, OH, and CH4are also discusse