Role of cuprous oxide in the autoxidation of aqueous sulphur dioxide and its atmospheric implications

Copper smelters emit sulphur dioxide and cuprous oxide concurrently In humi d atmosphere, aqueous cuprous oxide is likely to catalyse the autoxidation of sulphur dioxide. This led us to undertake the study of the kinetics of t he autoxidation of aqueous SO2 in aqueous Cu2O suspensions. In unbuffered s uspensions, the reaction is characterised by an induction period and the ra te law observed is: R-obs = k(2) [CU2O](0-5) [S(IV)][O-2](0.5). The value of k(2) was determined to be 1.26 x 10(-2) l mol(-.5) g(-0.5) s(- 1) at 30 degrees C and pH 5.5. Addition of 0.18 mol l(-1) ethanol did not a ffect the reaction. A free radical mechanism has been proposed to explain t he results. In acetate-buffered suspensions, in addition to the oxidation o f sulphur(IV) into sulphate, copper(I) is also autoxidised into copper(II). The atmospheric implications of this study are discussed. (C) 1999 Elsevie r Science Ltd. All rights reserved.