A hybrid model for predicting the distribution of sulphur dioxide concentrations observed near elevated point sources

A hybrid model, combining a deterministic model with a distributional model, is developed for predicting the distribution of ambient sulphur dioxide concentrations recorded near point sources. The deterministic component of the hybrid model is based upon the Gaussian plume model, while the distributional models are identified from amongst the two-parameter lognormal, Weibull and gamma, and the one-parameter exponential distribution models. Using the deterministic model component output calibrated about the 50-90 percentile concentrations, the hybrid model produces estimates of 24-, 8-, 3-, 1-, 0.5-h average sulphur dioxide data to an accuracy of a factor of 2 for the 98-percentile, second-highest and maximum concentrations. The effect of the method of calibration of the deterministic component upon the statistical component of the hybrid model is examined in detail.