Evaluation of a three-dimensional cloud chemistry model

To evaluate the effectiveness of a three-dimensional dynamical cloud model in simulating cloud water chemistry, the ion concentrations in simulated clouds are compared with the results of chemical analyses of collected cloud water samples. The model is initialized with surface and aircraft measurements of clear air chemistry. The data that are used in the evaluation come from non-precipitating cumulus clouds that were sampled during the Eulerian Model Evaluation Field Study (EMEFS I) that was conducted in central Ontario in the summer of 1988. Three different cases are considered. In general, the simulated ion concentrations agree well with the observed concentrations when the ambient aerosol is assumed to be activated with 1.00% efficiency. In two of the cases the predominant contribution to the cloud water sulphate is activation of the aerosol. In the third case, in which the clear air sulphate concentration is small, oxidation of sulphur dioxide by hydrogen peroxide and ozone is the dominant source of sulphate.