Experimental studies on aerosol particle formation by sulfur dioxide

Abstract

The formation and growth of aerosol particles of dilute sulfuric acid produced by photochemical oxidation of SO 2 (0.05–10 ppm. by volume) in purified air has been studied qualitatively in laboratory apparatus. The number of particles formed is strongly dependent on SO 2 concentration, relative humidity (< 10–80%) and u.v. light intensity. The number concentration increases rapidly to a maximum within a few minutes after the start of irradiation and then decreases slowly during the next 10 min. Particle size increases with irradiation time and is dependent on SO 2 concentration, and on relative humidity when the SO 2 concentration is less than 0.1 ppm. In the conditions employed the volumetric rate of formation of particles ranged from 0.15 to 18.7μm 3 cm −3. The overall quantum yield of photochemical reaction was 8 × 10 −3. The oxidation rate was 0.04% h −1: extrapolation of this rate to noonday sunlight in summer at latitude 35°N gives 0.7% h −1.