The photochemical role of tropospheric nitrogen oxides

Abstract

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 NO x (NO+NO 2 ) levels approaching 1 ppb in NO x source regions but less than 0.1 ppb outside source regions. Applying the new rate coefficients implies increased radical concentrations and a more intense O 3 and CO photochemistry. Even for densities of 0.1 ppb or less, NO x still leads to significant local O 3 production and conversion of HO 2 to OH. Unrealistic O 3 profiles are obtained with the new rate coefficients for surface NO x densities of about 1 ppb, while reasonable agreement with observation is obtained with lower NO x densities. Feedback processes between CO, NO x , OH, and CH 4 are also discussed. © 1978 by the Chinese Geophysical Society