Effects of Monochromatic UV-Visible Light and Sunlight on Fe(III)-Catalyzed Oxidation of Dissolved Sulfur Dioxide |
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Authors: | Email author" target="_blank">Yuegang?ZuoEmail author Jian?Zhan Taixing?Wu |
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Institution: | (1) Department of Chemistry and Biochemistry, University of Massachusetts Dartmouth, North Dartmouth, MA, 02747, U.S.A. |
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Abstract: | The effect of UV-visible light and natural sunlight on the Fe(III)-catalyzed oxidation of dissolved sulfur dioxide has been
studied under the conditions representative for those of acidified atmospheric liquids. The experimental results have shown
that both sunlight and UV-visible light enhance the rate of Fe(III)-catalyzed oxidation of aqueous sulfite with wavelength
ranging from 300 to 575 nm. The light enhanced oxidation is mainly due to photochemical formation of OH radicals from Fe(OH)2+ complexes in the wavelength region below 420 nm and SO3•− free radicals from Fe(III) sulfite complexes above 420 nm in the absence of organic ligands. Like the Fe(III)-catalyzed thermal
chemical oxidation, the Fe(III)-catalyzed photochemical oxidation is also first order with respect to sulfite ion concentration.
The sunlight irradiation can increase the Fe(III)-catalyzed oxidation of S(IV) over 45%. The presence of organic complex ligands,
such as oxalate, can completely inhibit the Fe-catalyzed oxidation of S(IV) in the dark. However, the photolysis of Fe(III)-oxalato
complexes generates oxalate free radicals, leading to the formation of H2O2 and OH radicals and the oxidation of S(IV). The rate of Fe(III)-catalyzed oxidation of S(IV) species is found to increase
with increasing light intensity. The effects of sunlight on the Fe(III)-catalyzed oxidation of S(IV) should be taken into
account when predicting the daytime rates of sulfuric acid formation in atmospheric water droplets. |
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Keywords: | atmospheric chemistry free radical iron sunlight photooxidation sulfur dioxide |
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