OH production rates in the troposphere

Abstract

The evaluation of OH radical reactions as a global sink for many trace gases in the troposphere requires a detailed knowledge of the OH production rate as a function of latitude and altitude. The OH production rate may be expressed as a product of the primary rate P 1 from the reaction of O( 1D) with water vapor and an amplification factor ƒ due to a re-cycling mechanism. The primary rate and its diurnal and seasonal averages have been computed as a function of latitude and altitude for the northern hemisphere, using only observational data for the involved parameters. For the southern hemisphere this procedure is not possible at present, because sufficiently detailed ozone measurements are not available. The calculation of the amplification factor requires in addition to the latitudinal distributions of atmospheric mixing ratios of CH 4 and CO, those of nitrogen dioxide for which observational data are almost entirely lacking. Accordingly the distribution of NO 2 mixing ratios was estimated to obtain values for the amplification factor ƒ. Effective OH production rates are given assuming that primary OH production rates obtained for the northern hemisphere are applicable also in the southern hemisphere. Due to the many uncertainties entering specifically into the values for the amplification factor the derived OH production rates must be considered a first approximation.