IRON(II)-CATALYZED PHOTOCHEMICAL DECOMPOSITION OF OXALIC-ACID AND GENERATION OF H2O2 IN ATMOSPHERIC LIQUID-PHASES

Although the iron(III)-catalyzed decomposition of organic acids and fo rmation of H2O2 in sunlit atmospheric water droplets has been well doc umented, field measurements have shown that a large fraction of the di ssolved iron in fogs, clouds, and rainwaters is present as reduced Fe( II) species. In this study, we report on Fe(II)-initiated photochemica l depletion of oxalic acid and formation of H2O2 in atmospheric water droplets. Our results show that the Fe(II)/Fe(III) couple is involved in the photocatalytic decomposition of oxalic acid and formation of H2 O2 with Fe(III) being the more active catalyst species. The initial ox idation state of iron is not critical for the catalytical processes, s ince the photochemical cycling between Fe(II) and Fe(III) occurs rapid ly in the atmospheric droplets. (C) 1997 Elsevier Science Ltd.