Primary and Secondary Glyoxal Formation from Aromatics:  Experimental Evidence for the Bicycloalkyl−Radical Pathway from Benzene, Toluene, and p-Xylene

Abstract

A new approach is presented to study the ring-cleavage process of benzene, toluene, and p-xylene (BTX). DOAS (differential optical absorption spectroscopy) was used for the simultaneous measurement of the respective ring-retaining products as well as glyoxal (a ring-cleavage product) in a series of experiments at the EUPHORE outdoor simulation chamber, Valencia/Spain. The good time resolution of the DOAS measurements (1-2 min) allowed the primary formation of glyoxal to be separated from any further contributions through additional pathways via reactions of stable intermediate compounds (secondary glyoxal formation). The ring-retaining products and glyoxal were identified as primary products. The primary glyoxal yield was found to be essentially identical to the overall yield of glyoxal formed over the time scale of the experiments. The negligible contribution from secondary glyoxal formation pathways was quantitatively understood for the experimental conditions of this study and was found to be representative for the troposphere. The yield of glyoxal was determined to be 35% ( 10% for benzene and about 5% higher for toluene and p-xylene. For benzene, the yield of hexadienedial was estimated to be e 8%. It is concluded that ringcleavage pathways involving the bicycloalkyl radical are major pathways in the oxidation of monocyclic aromatic hydrocarbons, i.e., BTX. The branching ratio for the bicycloalkyl radical intermediate, proposed to form from the reaction of the aromatic-OH adduct with atmospheric oxygen, could be directly identified with the primary glyoxal yield for the benzene system and as a lower limit in the case of toluene and p-xylene. Implications for the chemical behavior of aromatic hydrocarbons in the atmosphere are discussed.

Distributions and diurnal changes of low molecular weight organic acids and ^|^alpha;-dicarbonyls in suburban aerosols collected at Mangshan, North China

“…α-Dicarbonyls showed concentrations ranging from 3.5 to 289 ng m -3 , with an arithmetical average of 51.5 ng m -3 in daytime and 59.8 ng m -3 in nighttime. Glyoxal (Gly) and methylglyoxal (MeGly) are gas-phase oxidation products of numerous VOCs such as benzene, toluene, xylene (Volkamer et al, 2001), ethylene (Ervens et al, 2004), isoprene (Zimmermann and Poppe, 1996) and terpene (Fick et al, 2004), and could act as precursors of secondary organic aerosols via heterogeneous processes (Kroll et al, 2005;Liggio et al, 2005).…”

On-road vehicle emissions of glyoxal and methylglyoxal from tunnel tests in urban Guangzhou, China

“…Toluene is a major anthropogenic SOA precursor in highly industrialized areas like the Pearl River Delta region (Ding et al, 2012), and it is a precursor to form glyoxal and methylglyoxal (Volkamer et al, 2001;Nishion et al, 2010). From our tunnel study we observed that average mass ratios of glyoxal-to-toluene and methylglyoxal-to-toluene were 0.1 and 0.03, respectively.…”

“…Glyoxal and methylglyoxal can both formed from the oxidation of VOCs (Calvert et al, 2000(Calvert et al, , 2002Volkamer et al, 2001) and emitted directly from tailpipes and biomass burning Kean et al, 2001;Hays et al, 2002;Ban-Weiss et al, 2008), yet direct emissions were viewed as being minor when compared to the secondary formation (Volkamer et al, 2005;Fu et al, 2008). As for speciated carbonyls emitted by gasoline and diesel vehicles, data were mostly obtained from tunnel studies carried out in the United States more than a decade ago Kean et al, 2001;Hays et al, 2002), and the trends in carbonyl emissions from vehicles were thereafter reviewed by Ban-Weiss et al (2008).…”

Diurnal and temporal variations of water-soluble dicarboxylic acids and related compounds in aerosols from the northern vicinity of Beijing: Implication for photochemical aging during atmospheric transport

“…60±70 ng m -3 ) at night. Glyoxal (Gly) and methylglyoxal (MeGly) are produced by gaseous-phase oxidation from various VOCs including ethylene (Ervens et al, 2004), and toluene, benzene, xylene (Volkamer et al, 2001) as well as terpenes (Fick et al, 2004) and isoprene (Zimmermann and Poppe, 1996). Interestingly, Gly showed higher concentrations in daytime whereas MeGly is more abundant in nighttime (Table 2).…”