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Chemical reactions in frozen solution: A possible pathway for enhanced chemical transformation in freezing systems

Wednesday, May 26, 2004
Betterton (Atmospheric Sciences Dept, University of Arizona)

Dilute aqueous solutions of nitrous acid can be oxidized to nitric acid in >90% yield simply by freezing. This counterintuitive observation can been explained by the "freeze-concentration effect", which can be harnessed to drive many other types of chemical reactions that would not normally be expected to proceed at a significant rate. The freeze-concentration effect could provide new feedback mechanisms between cloud condensation nuclei and glaciated clouds; it could provide a further link between cloud formation and the atmospheric aerosols; and it could affect cloud droplet size distributions and therefore cloud albedos and the radiation budget. The freeze-concentration effect could also play an important role in the formation of acid precipitation since precursors of both sulfuric and nitric acids can be oxidized during freezing. The autoxidation of certain species such as iodide, bromide and some trace metals in seawater offers another intriguing possibility in maritime environments. Finally, we have recently shown that organic polymerization reactions can be enhanced by freezing. We will speculate on some possible implications for Europa.

Useful Reference:
Betterton,E.A., Anderson, D.J., 2001, "Autoxidation of N(III), S(IV) and other species in frozen solution - a possible pathway for enhanced chemical transformation in freezing systems", J. Atmos. Chem., 40, 171-189    

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