Products of the Gas-Phase Reactions of OH Radicals with p-Xylene and 1,2,3- and 1,2,4-Trimethylbenzene: Effect of NO₂ Concentration

Abstract

Products of the gas-phase reactions of the OH radical with p-xylene and 1,2,3-and 1,2,4-trimethylbenzene have been measured by gas chromatography in the presence of varying concentrations of NO 2 . Our product analyses show that the ring-cleavage products 2,3-butanedione (from 1,2,3-and 1,2,4-trimethylbenzene) and 3-hexene-2,5-dione (from p-xylene and 1,2,4-trimethylbenzene) exhibit a dependence of their formation yields on the NO 2 concentration, with higher yields from the reactions of the OH-aromatic adducts with O 2 than from their reactions with NO 2 . Furthermore, our data show that these ring-cleavage products are primary products of the OH-aromatic adduct reactions. Formation yields extrapolated to zero NO 2 concentration should be applicable to ambient atmospheric conditions (provided that there is sufficient NO that peroxy radicals react dominantly with NO), and are from p-xylene, p-tolualdehyde, 0.0706 ( 0.0042 (independent of NO 2 concentration), 2,5-dimethylphenol, 0.138 ( 0.016 (independent of NO 2 concentration), and 3-hexene-2,5-dione, 0.32 (extrapolated); from 1,2,3-trimethylbenzene, 2,3-butanedione, 0.52 (extrapolated); and from 1,2,4-trimethylbenzene, 2,3-butanedione, 0.10 (extrapolated) and 3-hexene-2,5-dione, 0.31 (extrapolated). Our formation yields of 3-hexene-2,5-dione from p-xylene and 1,2,4-trimethylbenzene are similar to those reported for glyoxal from p-xylene and of methylglyoxal from 1,2,4-trimethylbenzene and therefore suggest that these are coproducts, as expected from reaction schemes presented here.

Theoretical considerations of secondary organic aerosol formation from H-abstraction of p-xylene

“…Also consistent with previous experimental results [3,29], the reaction of IM3 with nitrogen oxide under the presence of NO is predicted to occur via two pathways by our calculations. One pathway is unimolecular decomposition via TS2 involving O 1 AO 2 cleavage.…”

“…Partially due to the complicacy of VOCs species, therefore the compositions of SOA formed from VOCs, and the difficulty in direct measurements of the highly reactive intermediates during the oxidation reaction [27,28], experimental ratification of the entire reaction course has not yet obtained [1,3,10,29,30]. Previous studies showed that in the presence of OH radical the main reaction path is OH addition to the aromatic ring to form a xylene-OH adduct (consuming $90% of OH radicals) with Habstraction from one methyl group to form a methylbenzyl radical (consuming $10% of OH radicals) being the minor route [18,[31][32][33][34].…”

Consecutive reactions of aromatic-OH adducts with NO, NO<sub>2</sub> and O<sub>2</sub>: benzene, naphthalene, toluene, m- and p-xylene, hexamethylbenzene, phenol, m-cresol and aniline

“…Atkinson and Aschmann (1994) observed a decrease of the yield of 2,3-butanedione from o-xylene with the expected curvature and a [NO 2 ] 1/2 value of about 2 ppm, confirmed by an experiment with fivefold decreased level of O 2 (RO 2 from the equilibrium (7/-7), see Volkamer et al (2002b). The decreasing yields of 2,3-butanedione from 1,2,3-trimethylbenzene and 1,2,4-trimethylbenzene with increasing NO 2 observed by Bethel et al (2000) can be taken as a hint at a similar competition of NO 2 with O 2 in the reaction with the OHadducts.…”

“…While tropospheric NO 2 levels (averaged over the region of benzene oxidation) are much lower than the 1.3 ppm value calculated for benzene, scavenging by NO 2 becomes important in high-NO x chamber experiments. Klotz et al (2002) to deliver 6% of phenol from benzene), Bethel et al (2000, yields of 3-hexene-2,5-dione from p-xylene), and Berndt and Böge (2003, yields of catechol from phenol decreasing from 73% in the absence to 35% at high NO 2 ), respectively. The agreement is excellent, except for phenol, where the chamber data imply a fivefold higher efficiency of NO 2 .…”

“…These aspects have been studied by laser photolysis/laser absorption and laser photolysis/UV absorption by Zellner et al (1985), , Bohn (2001), Johnson et al (2002Johnson et al ( , 2005, Raoult et al (2004) and Grebenkin and Krasnoperov (2004); by discharge-flow/laser induced fluorescence (Goumri et al, 1990); in flash photolysis/resonance fluorescence studies by Perry et al (1977), and Knispel et al (1990) for benzene, toluene and phenol; and in product studies by , Atkinson et al (1991), Atkinson and Aschmann (1994), Klotz et al (1998), Smith et al (1998, Bethel et al (2000), Berndt and Böge (2001a, 2001b, 2003 and Volkamer et al (2002a,b), Klotz et al (2002), Olariu et al (2002), Zhao et al (2005) and Coeur-Tourneur et al (2006) for benzene, toluene, o-, m-and p-xylene, 1,2,3-, 1,2,4-and 1,3,5-trimethylbenzene, HMB, phenol and o-, m-and p-cresol. In the following, we present a kinetic study of the consecutive reactions of aromatic-OH adducts in the presence of variable amounts of either NO, NO 2 or O 2 . Most of the results on benzene, toluene, p-xylene, phenol and m-cresol were obtained using the VUV flash photolysis/resonance fluorescence (FP/RF) technique, introduced by Stuhl and Niki (1972).…”