The kinetics of oxidation of sulphur dioxide within the plume from a sulphide smelter in a remote region

Abstract

The rate of oxidation of SO 2 has been determined in the plume of a smelter situated in a remote part of Australia. A strong diurnal effect has been demonstrated. Three major techniques have been employed in this study, namely correlation spectrometry, flame photometry and high-volume sampling. The first two methods have provided information on the overall rate of loss of SO 2 from the plume. Correlation spectrometry set an upper limit to this rate, in that less than 15% loss occurred over distances up to 236 km from the stack. Flame photometry was used to measure the fraction of the sulphur compounds in the plume that were gaseous. This fraction decreased from an initial 0.98 near the stack to 0.89 at a plume age of 10 h. However, this decrease correlated with the amount of insolation that the plume sample had received rather than plume age. Analysis of aerosol samples collected by high-volume filtration has demonstrated that the ratio of the concentration of SO 2− 4 to Pb increases with distance from the stack in a manner that correlates with insolation rather than age. (Pb is a minor component of the initial stack emission and is used as a conservative tracer.) These experiments have shown that oxidation proceeds only during the day, there being no detectable reaction at night. When diurnally averaged, the rate of oxidation (during the winter months at a latitude of 20°S) is 0.25%h −1. The oxidation process is interpreted to be gas phase homogeneous photooxidation involving the hydroxyl and hydroperoxy radicals.