The carbon kinetic isotope effects (KIEs) of the room temperature reactions of benzene and several light alkyl benzenes with OH radicals were studied in a reaction chamber at ambient pressure using gas chromatography coupled with online combustion and isotope ratio mass spectrometry (GCC‐IRMS). The KIEs are reported in per mil according to ɛ (‰) = (KIE − 1) × 1000, where KIE = k12/k13. The following average KIEs were obtained, (all in ‰): benzene 7.53 ± 0.50; toluene 5.95 ± 0.28; ethylbenzene 4.34 ± 0.28; o‐xylene 4.27 ± 0.05, p‐xylene 4.83 ± 0.81; o‐ethyltoluene 4.71 ± 0.12 and 1,2,4‐trimethylbenzene 3.18 ± 0.09. Our KIE value for benzene + OH agrees with the only reported value known to us [Rudolph et al., 2000]. It is shown that measurements of the stable carbon isotope ratios of light aromatic compounds should be extremely useful to study atmospheric processing by the OH radical.

No abstract

[1] A three-dimensional global chemical tracer model of the atmosphere has been adapted to include the stable carbon isotopic composition and isotopic fractionation of ethane and benzene. For computational efficiency the chemistry was based on a prescribed OHradical concentration field, and therefore the feedback of ethane and benzene chemistry on the atmospheric OH-radical concentrations was not considered. The Emission Database for Global Atmospheric Research (EDGAR) V2.0 emission database used needed to be scaled by a factor of 2.22 in order to have good agreement between observed and modeled concentrations. Modeled isotopic compositions were consistent with the few published observations. The global distribution of modeled stable carbon isotope ratios and the derived mean photochemical ages of ethane and benzene are presented. The model predicts distinct regimes of photochemical aging and air mass mixing for polar regions.

No abstract