Development of an air quality model for BCL Limited

Abstract

In order to understand the impact from a point source of pollution a comprehensive air quality monitoring programme must be in place. Measurement stations are at fixed locations and can only measure the relevant concentration if the wind is blowing in a particular direction. With changing wind direction, a measurement station needs to be coupled with a dispersion model to predict the impact from a point source, such as the BCL Limited smelter. The smelter produces 55 500 tonnes per annum of nickel/copper granules; in the process emitting waste gases to the atmosphere through a 153 m stack. The EEGAIR-BCL1. dispersion model was developed for BCL Limited to complement the air quality monitoring programme in the Selebi-Phikwe area. The model was developed for the smelter specifically, using local meteorological data at Selebi-Phikwe and smelter specific emission data. Results from the model were tested against data obtained from existing measurements stations at Selebi-Phikwe for May 2002, using statistical analyses. The average index of agreement indicates that the model predictions were more accurate for Kopano (0,44) and SPSS (0,25) stations than for WUC (0,08) station. Yearly averaged emission data was used for model input and better correlation can be expected when using actual hourly and/or monthly emission data. Based on the EEGAIR-BCl1 dispersion model results, it was found that the highest impact from the smelter stack was at a distance of 4 km to 7 km west from the stack. The model results indicate that, on average, the impact from the smelter stack in residential areas of Selebi-Phikwe was between 0 and 50 µ/m3 for May 2002.