Kinetics of NO3 uptake on a methane soot coating

The dependence of the initial rate of NO3 uptake on a methane soot coating at two temperatures (256 and 297 K) and NO3 concentrations of 2.4 x 10(12) to 3.6 x 10(13) cm(-3) is studied using a flow reactor with a movable insert and mass-spectrometric detection. It is found that, in this concentration range, the uptake of NO3, unlike that of NO2 and N2O5, occurs by the impact recombination mechanism. It is demonstrated that, before being deactivated, each active surface site destroys similar to 100 and similar to 150 NO3 radicals at 297 K and 256 K, respectively. The uptake coefficient calculated per specific BET surface of the soot coating depends on the exposure time as gamma(t) = gamma(0)exp(-t/tau), where gamma(0) and tau are NO3-concentration-dependent parameters. Based on the Langmuir concept of adsorption, the elementary parameters that control the uptake process are determined, such as the desorption rate constant k (d) = nu (d)exp(-Q (ad)/RT) at nu(d) = 3 x 10(9) s(-1) and the heat of adsorption, Qad = 42.6 kJ mol(-1), as well as the rate constant of the bimolecular heterogeneous reaction of deactivation of active surface sites, k (r) = A (r)exp(-Ea/RT), with A (r) = 1.1 x 10(-11) cm(3) s(-1) and E (a) = 9.5 kJ mol(-1).