The dependence of the concentration of OH on its precursors under moderately polluted conditions : a model study

Atmospheric trace-gas oxidation is initiated by free radicals. Of these, the hydroxyl radical is the most important daytime initiator, because of its universal ability to react with pollutants, which begins the process of removing the pollutants from the atmosphere. The concentration of the hydroxyl radical is an index of the capacity for atmospheric oxidation, because it often determines the rate of pollutant removal. The effects of various precursors, including nitrogen oxides, carbon monoxide, hydrocarbons, formaldehyde, ozone, and peroxyacetylnitrate on hydroxyl radical concentration were studied. In addition, photolysis rates were correlated with concentrations. Nitrogen oxides are the most important influence on hydroxyl radical concentration, and it played a role in the activity of all other precursors. In the presence of high-NO sub(x)concentrations hydrocarbons and CO do not affect the hydroxyl radical concentration. Mathematic models of air masses are accurate only under low-NO sub(x) concentration conditions.