OXIDATION OF SULPHUR DIOXIDE IN POWER STATION PLUMES

Some theoretical estimates are made of the rate of growth of H2SO4 droplets nucleated by MnSO4 crystallites in a humid, SO2 polluted atmosphere. Comparison with experiment suggests that, as the acid concentration within the droplet rises, the rate of growth decreases as a result of the product acid affecting the rate of SO2 oxidation. For this reason the amount of droplet growth, and the amount of SO2 oxidation, is very sensitive to the ambient humidity, and will be greatest for saturated or very high relative humidities where droplet acid concentrations are restricted to low values. Similar calculations relating to the dusty conditions present in power station plumes are also made. These show that the rates of SO2 oxidation observed in these systems can be accounted for by the catalytic qualities of the iron present in the effluent dust. It is suggested that other oxides present also play an important part in this process in that they react with the product acid as it is formed, thus keeping the droplet in a neutral condition in which the catalyst is most active. © 1969.