Kinetics of NO2 uptake on methane flame soot

The dependences of the initial NO2 uptake coefficient γ on a methane soot coating at 255 K on the NO2 concentration (1.3 × 1012–3.3 × 1013 cm–3) and time t were studied using a flow reactor with a mobile insert and mass spectrometric recording of gaseous reagents and products: 1/γ(t) = 1/γ0 + at, where γ0 and a are the parameters that depend on the NO2 concentration; γ0 = γ0 ini/(1 + k L [NO2], a= k [NO2], with the constants γ0 ini = (4.8 ± 2) × 10–4, K L = (8.2 ± 3) × 10–13 cm3, and k = (2.3 ± 0.1) × 10–10 cm3 s–1. The elementary parameters that determine the uptake were evaluated on the basis of the Langmuir adsorption model: desorption rate constant k d = (52 ± 20) s–1, adsorption heat Q ad = (38 ± 8) kJ mol–1, rate constant of the unimolecular heterogeneous conversion of NO2 into the product k r = (2.5 ± 1.3) × 10–2 s–1, and its activation energy E a = (19 ± 10) kJ mol–1. The laboratory data were extrapolated, based on the uptake coefficient, to the limiting tropospheric NO2 concentrations in remote marine (1 ppb) and polluted industrial regions (40 ppb).