Photolysis in aqueous aerosols: 300 nm yields of Fe2+ from a ferrioxalate actinometer and of OH radical from nitrate ions

Abstract

300 nm photolysis yields of Fe²⁺ from potassium ferrioxalate and of OH from nitrate ion have been measured in aqueous aerosols, the yield from ferrioxalate in a bulk solution being used to measure the light intensity. Mie theory was used to calculate effective cross-sections for absorption and scattering of light by the aerosol droplets. Yields of OH from nitrate ion have been measured with benzoic acid and carbon monoxide radical scavengers. The photolysis yield of Fe²⁺ from ferrioxalate was found to be enhanced in the aerosol by a factor of 48 ± 17. This enhancement is believed to be real, and is attributed to surfactant behaviour that results in the presence of a high concentration of ferrioxalate in a region of high light intensity near the droplet surface. The experiments with benzoic acid indicate that the yield of OH from nitrate in aerosol droplets is not significantly different from the yield in bulk solution. The CO experiments appear to indicate that the total OH production in the aerosol is enhanced over that in bulk solution by a factor of 10 ± 3, but this number is not considered reliable.