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

S. Kamm, H. Saathoff, K.-H. Naumann, O. Möhler, U. Schurath

Forschungszentrum Karlsruhe, Institute of Meteorology and Climate Research, POB 3640, D-76021 Karlsruhe, Germany

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Abstract

The rates of gasification of soot (produced in a spark generator) by 1 vol% ozone in the temperature range 22–

105 ◦C, and by 1000 ppmv nitrogen dioxide at 200–350 ◦C, 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 ◦C. To avoid shielding effects, <500 µg 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 γ (T ) = (gasification rate)/(surface

collision rate of oxidant molecules). These probabilities ranged from 2.9 × 10−11 at 22 ◦C to 8.6 × 10−10 at

105 ◦C for ozone, and from 1.2 × 10−9 at 200 ◦C to 4 × 10−8 at 350 ◦C for nitrogen dioxide. The gasification

rate of diesel soot exceeded that of soot from the spark generator at 300 ◦C by a factor of 2. The temperature

dependencies deviate from Arrhenius behavior at low temperatures. Parameterizations are proposed to interpolate

γ (T ) in the investigated temperature ranges and to extrapolate γ (T ) to higher temperatures.