title: Identification of Nitration Products during Heterogeneous Reaction of NO2on Soot in the Dark and under Simulated Sunlight.
abstract: Author: The present work, involving the formation of NO and nitrous acid (HONO) and the nitration of polycyclic aromatic hydrocarbon (PAHs) to nitro-PAHs as well as the uptake coefficients of NO2, has been performed on a normal-pressure flow reactor to identify the nitration products during the heterogeneous reaction of soot toward NO2in the dark and under simulated sunlight. Two types of soot particles, namely the commercial black carbon (BC) and the diesel engine soot (ES), were selected as the studied soot to compare the impacts of soot properties on heterogeneous nitration. During the whole reaction on either of the two studied soots in the dark, a fast reversible physical adsorption is observed at the very beginning, followed by a slow irreversible chemical conversion from NO2to HONO and NO, in good agreement with the "reduction-oxidation" mechanism. HONO is the most abundant product during the nitration reaction on the two studied soots, contributing to 70-90% of consumed NO2after 50 min exposure. Reaction orders of NO2for HONO are determined as 1.20 ± 0.07 and 1.31 ± 0.04 for BC and ES, respectively, which are both close to first-order. Moreover, four sorts of PAHs compounds and their five nitro-derivatives have been identified and quantified during the reaction. About 40% and 20% of the total four measured PAHs are consumed on BC and ES, respectively, resulting in an increase in the total five measured nitro-PAHs by 21-fold on BC and 2.8-fold on ES. Finally, the impacts of light on gaseous and organics products have been investigated and the results confirm that simulated sunlight can enhance the reactivity of PAHs toward NO2and cause the photolysis of newly formed nitro-compounds with more HONO formation, strongly suggesting that photochemistry of soot in the presence of NO2is of great importance to be a photochemical source of HONO and would also influence the fates of PAHs and nitro-PAHs on soot.
authors.affiliation: Key Laboratory for Power Machinery and Engineering of M. O. E, Shanghai Jiao Tong University , Shanghai 200240, China.
authors.forename: Chun
authors.identifier: http://orcid.org/0000-0001-7748-2632
authors.initials: C
authors.lastname: Guan
authors.affiliation: Key Laboratory for Power Machinery and Engineering of M. O. E, Shanghai Jiao Tong University , Shanghai 200240, China.
authors.forename: Xinling
authors.initials: X
authors.lastname: Li
authors.affiliation: Key Laboratory for Power Machinery and Engineering of M. O. E, Shanghai Jiao Tong University , Shanghai 200240, China.
authors.forename: Wugao
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Key Laboratory for Power Machinery and Engineering of M. O. E, Shanghai Jiao Tong University , Shanghai 200240, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Huang