Heterogeneous Reaction of NO₂on Hexane Soot:  A Knudsen Cell and FT-IR Study

In this study, the reaction of NO 2 on freshly prepared hexane soot has been studied using a Knudsen cell reactor and FT-IR spectroscopy. Initial uptake coefficients were determined using gas-diffusion models that account for the surface area of the top layer of soot particles as well as the accessible underlying layers of soot particles. Under dry conditions, the initial uptake coefficient was found to be near 5 × 10 -5 at a gas concentration of 2.5 × 10 11 molecules cm -3 and a temperature of 295 K. In addition to reporting an initial uptake coefficient, uptake coefficients averaged over time and/or coverage are reported so as to compare to other values in the literature. Accounting for the increased surface area due to the underlying layers of soot particles, there is better agreement between the value of the uptake coefficient reported here using a Knudsen cell reactor and values determined from other experimental methods. The total amount of NO 2 reacted per unit surface area of soot and the conversion of NO 2 to HONO have been quantified. From these data, the atmospheric implication of the heterogeneous reaction of NO 2 on soot particles to form HONO is discussed.