Mechanistic study on photochemical generation of I•/I2•- radicals in coastal atmospheric aqueous aerosol

The reactive iodine species may exhibit significant impacts on many global atmospheric issues and the I-center dot/I-2(center dot-) radicals play key roles for inducing the formation of these reactive iodine species. However, the current understanding on the formation of I-center dot/I-2(center dot-) radicals in atmospheric aqueous aerosol is still quite limited. The results reported herein suggest that I-center dot/I(2 center dot-)can be produced simultaneously in aqueous aerosol by several sunlight-driven photochemical pathways including direct photo-dissociation of soluble organic iodine (SOI) at rates of 0.10-1.34 x 10(-9) M ns(-1) and 0.99-5.68 x 10(-7) M mu s(-1),(OH)-O-center dot-mediated oxidation of I- at 0.03-1.41 x 10(-8) M ns(-1) and 0.05-4.10 x 10(-6) M mu s(-1) , and 3DOM*-induced oxidation of I- at 1.57-1.65 x 10(-9) M ns(-1) and 0.99-5.68 x 10(-7) M mu s(-1) for generation of I-center dot and I-2(center dot-) , respectively. Meanwhile, the pathway of e(aq)(-)-initiated stepwise reduction of IO3- to I-2(aq) and further photolyzed into I-center dot plays negligible role in formation of I-center dot/I-2(center dot-) due to the low reaction rates and severe quenching effect of e(aq)(-) by dissolved O-2. Our work presented the new data on mechanism and kinetics for comprehensive elucidation of I-center dot/I-2(center dot-) formation in coastal atmospheric aqueous aerosol and would help to better understand the transformation mechanism of iodine species, pathways of iodine cycling and the associated environmental impacts involving atmospheric reactive iodine radicals.

Automated summary

This study investigates the mechanism of I·/I2·- radical formation in atmospheric aqueous aerosol, revealing that the radicals can be simultaneously produced through direct photo-dissociation, oxidation reactions, and 3DOM*-induced oxidation.