  Compound-specific stable carbon isotope ratios for phenolic compounds in
secondary particulate organic matter (POM) formed by photooxidation of toluene
were studied. Secondary POM generated by photooxidation of toluene using a
continuous-flow reactor and an 8 cubic meter indoor smog chamber was collected,
and then extracted with acetonitrile. Eight phenolic compounds were identified
in the extracts by a gas chromatograph coupled with a mass spectrometer, and
their compound-specific stable carbon isotope ratios were determined by a gas
chromatograph coupled with a combustion furnace followed by an isotope ratio
mass spectrometer. The majority of the products, including methylnitrophenols
and methylnitrocatechols, were isotopically depleted by 5 to 6 permil compared
to the initial isotope ratio for toluene, whereas the isotope ratio for
4_nitrophenol remained the same as the initial isotope ratio for toluene. Based
on the reaction mechanisms postulated in literature, stable carbon isotope
ratios of these products were calculated. Comparison of the observed isotope
ratios with the predicted implies that a reaction channel of
methylhydroxycyclohexadienyl radical with NO2 is a possible production pathway
for the particulate phenolic compounds.
