Modeling the Time-Dependent O3 Uptake on a Methane Flame Soot Coating Under Conditions of Competitive O3/NO2 and O3/N2O5 Adsorption

The uptake of O-3 (1 x 10(12)-5x 10(13) cm(-3)) on a methane soot coating preliminarily exposed to N2O5, is studied using a flow reactor with a movable insert. Based on the dependence of the ozone uptake coefficient on the exposure time and O-3 concentration, the uptake mechanism is established and a number of elementary parameters are obtained that describe the uptake process at arbitrary O-3 concentrations. Based on the Langmuir representation of adsorption, a model description of the uptake on soot under conditions of the competitive adsorption of O-3/NOx, where NOx = NO2 and N2O5, taking into account the multistage uptake process, is proposed. Based on the developed model and elementary parameters describing the uptake of O-3, NO2, and N2O5 on a fresh soot surface, as well as the uptake of ozone on a surface pretreated with NO2 and N2O5, numerical estimates were made of the additional contributions to the ozone uptake for two real scenarios of the O-3/NOx ratio. For an industrial region in winter, when the ozone concentration is minimal (10 ppb O-3, 17 ppb NO2, and 4 ppb N2O5), the additional integral contribution to the uptake of O-3 on the reaction products of NO2 with soot is 68%, and in the case of N2O5, it is 3.6%. For the same region in summer, at the maximum ozone concentration (36 ppb O-3, 17 ppb NO2, and 4 ppb N2O5), the analogous contributions will be 20 and 1%, respectively. The reasons for this difference are discussed.