Dependence of the OH concentration on solar UV

Abstract

OH and the major parameters determining its concentration were measured during a field campaign in August 1994 at Mankmoos, a rural, relatively unpolluted site in northeastern Germany. The measured OH concentrations were previously shown to depend mainly on the intensity of solar UV and on the mixing ratio of NO2. In this paper we develop a simple parameterization of the dependence on solar UV and on NO2. The photolysis of O3 to O1D, of NO2 to NO, and of HCHO to HCO and H, all contribute significantly to the total dependence of OH on solar UV. We demonstrate that the photolysis frequency of O3, JO1D, is a suitable measure for that dependence which is slightly less than linear. The highly nonlinear dependence of OH on NOx is approximated by a Padé function. The parameterization provides a tool for a future quantitative intercomparison of the measured and modeled dependences of OH on UV and NO2. It also allows the removal of the variation in the measured OH induced by the dependences on the variables, UV and NO2, and thus enables a search for dependences on other, less influential parameters.