Laboratory Studies on the Carbon Kinetic Isotope Effects on the Production Mechanism of Particulate Phenolic Compounds Formed by Toluene Photooxidation: A Tool to Constrain Reaction Pathways

摘要

Compound-specific stable carbon isotope ratios for phenolic compounds insecondary particulate organic matter (POM) formed by photooxidation of toluenewere studied. Secondary POM generated by photooxidation of toluene using acontinuous-flow reactor and an 8 cubic meter indoor smog chamber was collected,and then extracted with acetonitrile. Eight phenolic compounds were identifiedin the extracts by a gas chromatograph coupled with a mass spectrometer, andtheir compound-specific stable carbon isotope ratios were determined by a gaschromatograph coupled with a combustion furnace followed by an isotope ratiomass spectrometer. The majority of the products, including methylnitrophenolsand methylnitrocatechols, were isotopically depleted by 5 to 6 permil comparedto the initial isotope ratio for toluene, whereas the isotope ratio for4_nitrophenol remained the same as the initial isotope ratio for toluene. Basedon the reaction mechanisms postulated in literature, stable carbon isotoperatios of these products were calculated. Comparison of the observed isotoperatios with the predicted implies that a reaction channel ofmethylhydroxycyclohexadienyl radical with NO2 is a possible production pathwayfor the particulate phenolic compounds.