Gasification of a soot aerosol by O3 and NO2:: Temperature dependence of the reaction probability

The rates of gasification of soot (produced in a spark generator) by 1 vol% ozone in the temperature range 22-105 degreesC, and by 1000 ppmv nitrogen dioxide at 200-350 degreesC, were determined by measuring the change in mass of carbon as a function of exposure time. The gasification of soot from a diesel engine by NO2 was also determined at 300 degreesC. To avoid shielding effects, less than or equal to500 mug of soot aerosol was deposited on 200 mg of loosely packed quartz wool plugs and exposed to the oxidizing gases in a flow system. The gasification rate of soot from the spark generator was considered in terms of the dimensionless reaction probability gamma(T) = (gasification rate)/(surface collision rate of oxidant molecules). These probabilities ranged from 2.9 x 10(-11) at 22 degreesC to 8.6 x 10(-10) at 105 degreesC for ozone, and from 1.2 x 10(-9) at 200 degreesC to 4 x 10(-8) at 350 degreesC for nitrogen dioxide. The gasification rate of diesel soot exceeded that of soot from the spark generator at 300 degreesC by a factor of 2. The temperature dependencies deviate from Arrhenius behavior at low temperatures. Parameterizations are proposed to interpolate gamma(T) in the investigated temperature ranges and to extrapolate gamma(T) to higher temperatures. (C) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.