PHOTOCHEMICAL DECOMPOSITION OF OXALIC, GLYOXALIC AND PYRUVIC-ACID CATALYZED BY IRON IN ATMOSPHERIC WATERS

Kinetics of the iron(III) catalysed photochemical degradation of oxalic, glyoxalic and pyruvic acids has been investigated under conditions representative of atmospheric waters. Degradation rates for the organic acids are proportional to the concentration of iron (III)-substrate complexes and sunlight intensity. Under September noon sunlight irradiation (0.65 m Einstein m-2 s-1), 1 muM dissolved iron(III) has a potential to catalyse the degradation of oxalic acid at a rate of 10 +/- 1 nM s-1; of glyoxalic acid, 7 +/- 1 nM s-1; and of pyruvic acid, 8 +/- 1 nM s-1. The half life for the photolysis of oxalic acid and alpha-keto acids catalysed by iron(III) is in the order of a few minutes whenever the concentration of dissolved iron(III) is comparable to that of the organic acids. A detailed reaction mechanism has been proposed in which the complex formation between iron(III) and the substrate is a key step. The evidence, that such an iron(III) catalysed photochemical process serves as a major removal pathway for atmospheric oxalic and alpha-keto acids, has also been discussed.