Soot samples from a spark generator, a flame, and a diesel passenger car were either collected on a Teflon filter and transferred to an IR-transparent window or deposited directly from a flame onto the window and investigated by Fourier transform infrared (FTIR) spectroscopy. The soot-covered windows were mounted in a 10 cm vacuum cell connected to a standard flow system with He as carrier gas. Reactive gases, such as NO2 and HNO3, were added to the carrier gas flow at a concentration of (0.016 to 2.5) × 1014 molecule cm-3. FTIR spectra of soot samples before and after exposure to HNO3, NO2, and O3 are presented. Formation of IR absorption bands was analyzed as a function of exposure time. IR bands attributable to soot surface oxidation products and nitrogen containing species, e.g. −CO, R−NO2, R−ONO2, and R−ONO were observed. The observed time dependence of the absorption bands of the spark generator soot can be fitted by two parallel reactions, a slow and a fast process. Both processes have a reaction order of n ≈ 0.2 (±0.3) for the NO2 + soot reaction and n ≈ 0.5 (±0.6) for the HNO3 + soot reaction. The number of active sites, N max = 2.2 × 1014 molecules cm-2 soot surface, has been estimated from saturation experiments. Surface reaction probabilities depend on reactant concentration and reaction time and were in the range of γ ≈ 10-6 to 10-8 for the slow, and γ ≈ 10-3 to 10-6 for the fast processes. The reaction probability on diesel engine soot was nearly 1 order of magnitude slower. It is concluded that the reaction of NO2 with soot cannot account for the HONO levels observed in urban air.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.