Ozone aqueous chemistry

The role of oxygen derived short-lived radical species in AOPs is still a field of active research. However, extensive knowledge has been accumulated on the mechanism of ozone aqueous chemistry (Rice, 2001, Gottschalk, 2000, Hoigne, 1998). The decomposition of molecular ozone in water by a radical-type chain reaction involves species such as hydrogen trioxide (HO ) with a lifetime of about 10 ps and HO radicals. The latter equilibrate with their dissociation products in about 30 ps, i.e. O3 and OH (Hoigne, 1998) or they decompose into O2 and HO promoting the chain reaction. 

Interfacial mass transfer of trace gases into aqueous pnase is investigated in a UV absorption-stop flow apparatus. For the first time, the mass accommodation coefficients are determined for O3 (5.3x10" ) and for SO2 (>2x10 2) The results are incorporated into a simple model considering the coupled interfacial mass transfer and aqueous chemistry in cloud drops. It is shown that dissolution of O3 into a drop is fast compared with its subsequent oxidation of dissolved S02 In addition, the conversion rate of S(IV) to S(VI) in aqueous drops by ozone reactions is not limited by interfacial resistance. 

The rate of aqueous ozonation reactions is affected by various factors such as the pH, temperature, and concentration of ozone, substrate, and radical scavengers. Kinetic measurements have been carried out in dilute aqueous solution on a large number of organic compounds from different classes (56,57). Some of the chemistry discussed in the foUowing sections occurs more readily at high ozone and high substrate concentrations. 

Tomiyasu, H Fukutomi, H Gordon, G. Kinetics and mechanism of ozone decomposition in basic aqueous soiution. inorganic Chemistry, 1985 24 (19), 2962-2966. 

The aqueous-phase and gas-phase chemistries of HO, are sufficiently closely coupled that the chemistry shown in Tables 8.11 and 8.12 can affect gas-phase concentrations as well. For example, including the aqueous-phase chemistry in models of tropospheric ozone formation alters predicted 03 concentrations, although whether the perturbation is significant is subject to some controversy (e.g., see Lelieveld and Crutzen, 1990 Jonson and Isaksen, 1993 Walcek et al., 1997 Liang and Jacob, 1997). 

Liang, J., and D. J. Jacob, Effect of Aqueous Phase Cloud Chemistry on Tropospheric Ozone, J. Geophys. Res., 102, 5993-6001 (1997). 

The chemistry of ozone in aqueous solutions and the health effects are complex. It is clear that ozone reacts with water products in the water supply to form numerous disinfection byproducts. However, the general pattern that emerges from most studies is that the reaction byproducts of ozonation appear to be less toxic than those produced by chlorination. 

Forni L, Bahnemann D, Hart E J (1982) Mechanism of the Hydroxide Ion Initiated Decomposition of Ozone in Aqueous Solution, Journal of Physical Chemistry 86 255-259. 

Tomiyasu H, Fukutomi H, Gordon G (1985) Kinetics and Mechanisms of Ozone Decomposition in Basic Aqueous Solutions, Inorganic Chemistry 24 2962-2985. 

Hoigne J (1998) Chemistry of Aqueous Ozone and Transformation of Pollutants by Ozonation and Advanced Oxidation Processes, in The Handbook of Environmental Chemistry Vol. 5 Part C, Quality and Treatment of Drinking Water II, ed. by J Hrubec, Springer- Verlag, Berlin, Heidelberg. 

Yes there are reactions involving dissolved ozone, even photochemical reactions which can produce free radicals. However given the atmospheric abundance of ozone of about 20-40 ppbv and its very low solubility, it can be easily shown that the ozone concentration in cloudwater is low — about 10 moles per liter — and hterefore that homogeneous aqueous-phase ozone reactions have a negligible effect on cloud and precipitation chemistry. 

Green solutions believed to be Am are prepared by oxidation of Am in concentrated aqueous basic solution by either ozone or the O radical. In contrast to Np, and similar to Pu, Am is unstable and reduces to the hexavalent state within minutes. A review on the chemistry of heptavalent transplutonium elements can be found in the Handbook of the Physics and Chemistry of the Actinides. ... 

Hoign4 J (1998) Chemistry of aqueous ozone and transformation of pollutants by ozonation and advanced oxidation processes. In Hrubec J (ed) The Handbook of Environmental Chemistry, vol 5. part C. Quality and Treatment of Drinking Water 11. Springer, Berlin Heidelberg New York... 

Cloud processes have been predicted to have a significant effect on the chemistry of the clean troposphere (Lelieveld and Crutzen, 1990, 1991 Warneck, 1991, 1992). For example, the uptake of HCHO, HOz radicals, and N2Os into cloud droplets can lead to a decrease in the production of ozone. Removal of HCHO reduces the rate of gas-phase production of HOz radicals, and N205 into cloud droplets can lead to a decrease in the production of ozone. Removal of HCHO reduces the rate of gas-phase production of H02 radicals [reactions (33)—(36)1, and consequent conversion of NO to N02. Also, aqueous-phase reactions of H2C(OH)2, the hydrated form of HCHO, lead to the formation of 02, which can react with dissolved 03 to enhance the rate of transfer of 03 to the liquid phase over that based solely on physical solubility. Absorption of N2Os into... 

Hoigne, J. 1984. Kinetics of reactions of aqueous ozone and of its decomposition products. Paper presented at Conference on Gas-Liquid Chemistry of Natural Waters, Brookhaven, NY. Abstracts, pp. 13-1 to 13-6. 

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