Abstract
Locally measured tropospheric OH concentrations are compared with model calculations to study the influence of chemical precursors and sunlight. The chemical scheme was taken from the gas phase reaction mechanism of the Regional Acid Deposition Model, which includes an explicit inorganic and a comprehensive organic chemistry. The experimental investigations probed planetary boundary layer air in two sets of campaigns. In Deuselbach (1983) and Schauinsland (1984) rural conditions were encountered with NOx concentrations on the average of 2.2 ppb and 0.9 ppb, respectively. This dataset was already compared with model results based upon an older and less detailed chemical reaction scheme (Perner et al.). Since then, the experimental data were reanalyzed leading to modified measured OH concentrations and also to modified precursor concentrations. For a consistent comparison with the more recent campaigns in Jülich (1987 and 1988) the calculations have been redone. The modeled and experimental OH concentrations of the campaigns in 1983 and 1984 correlate well with a coefficient of correlation of r=0.73. On average the model overpredicts OH by about 20%. Under more polluted conditions in Jülich with average NOx, mixing ratios of 4 ppb, the correlation coefficient between experimental and modeled data are significantly smaller (r=0.61). Again the model overpredicts the OH concentration by about 15%, somewhat less than for the rural case. The precision of the comparison is limited by the uncertainties of the chemical reaction rate constants.
