Abstract

Studies on the kinetics of soot-O<sub>3</sub> reactions, at various soot and ozone concentrations, have been conducted under flow conditions with ozone ranging from 50 to 15,000 ppm and soot from 2 to 350 mg. At lower concentrations, the initial rates of CO<sub>2</sub> and CO formation are found to be half order with respect to soot and first order with respect to ozone. At higher concentrations, CO<sub>2</sub> formation exhibits a more complex pattern. The initial rate for the formation of CO<sub>2</sub> for a first stage is half order with respect to soot and 1.5 order with respect to O<sub>3</sub>, while the second stage is zero order in both species. Differences between data at higher and lower concentrations are discussed, and mechanisms for the formation of CO<sub>2</sub>, CO, and carboxylics during ozonation are suggested. Mass balance calculations on low concentration data reveal that only a small portion of the ozone is used to produce CO<sub>2</sub>, CO, H<sub>2</sub>O, and carboxylic species, most of it being decomposed catalytically over soot. At higher concentrations of O<sub>3</sub>, the rate of formation of carboxylic functionalities during the hexane soot-ozone reaction under static conditions has been examined. The initial rate, as determined by the Elovich equation, suggests that the soot-ozone reaction is nearly 6 times faster under equivalent conditions than the soot-NO<sub>2</sub>/N<sub>2</sub>O<sub>4</sub> reaction reported earlier from this laboratory.

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