The chemical kinetics of HONO formation resulting from heterogeneous interaction of NO₂ with flame soot

Abstract

Uptake experiments at ambient temperature of NO 2 on ethylene, acetylene and toluene soot resulted in significant amounts of HONO. The initial uptake coefficient γ0 of NO 2 on ethylene soot decreased from 0.12 to 0.03 with increasing NO 2 concentration in the range 8×10 10 to 1.4×10 13 molecule s −1 . The HONO yields relative to NO 2 taken up were in the range 50 to 93% and were consistent with a mechanism in which either soot or hydrogen contained in it was the reducing agent. The branching ratio of the yield of HONO and NO was a function of the sampling spot at which the soot was collected within a diffusion flame and ranged from 23 to 2.2 with increasing distance from the flame base and thus age. The total amount of HONO generated in one uptake experiment was 1.2×10 16 molecules per mg of soot. Heating cycles bring back the ability of soot to generate HONO, but at diminishing yields.