Role of Organic Carbon in Heterogeneous Reaction of NO_2 with Soot

摘要

A large uncertainty among the reported uptake coefficients of NO_2 on soot highlights the importance of the composition of soot in this reaction. Soot samples with different fractions of organic carbon (OC) were prepared by combusting n-hexane under controlled conditions. The heterogeneous reaction of NO_2 on soot was investigated using a flow tube reactor at ambient pressure. The soot with the highest fuel/oxygen ratio showed the largest uptake coefficient (γ_(initial)) of NO_2 and yield of HONO (y_(HONO))- Compared to fresh soot samples, preheated samples exhibited a great decrease in uptake coefficient of NO_2 and HONO yield due to the removal of OC from soot. Ozonized soot also showed a lower reactivity toward NO_2 than fresh soot, which can be ascribed to the consumption of OC with a reduced state (OC_R). A linear dependence of the NO_2 uptake coefficient and yields of HONO and NO on the OC_R content of the soot was established, with γ_(initial)(NO_2) = (1.54 ± 1.39) X 10~(-6) + (1.96 ± 0.35) × 10~(-7) × OC_R, y_(HONO)= (11.6 ± 16.1) + (1.3 ± 0.40) × OC_R, and y_(NO) = (13.1 ± 1.9) - (0.2 ± 0.05) × OC_R, respectively.