Volatile organic compounds up to C20 emitted from motor vehicles; measurement methods

To understand better the sources of observed differences between on-road vehicle emissions and model estimates, and to evaluate the emission of ozone precursors from motor vehicles, a series of experiments was conducted in the Fort McHenry Tunnel, Baltimore, Maryland (18–24 June 1992), and in the Tuscarora Mountain Tunnel, Pennsylvania (2–8 September 1992). Samples were collected using stainless steel canisters (whole air samples, analyzed for C2---C12 hydrocarbons), Tenax-TA solid adsorbent cartridges (for semi-volatile hydrocarbons, in the C8---C20 range), and 2,4-dinitrophenylhydrazine (DNPH) impregnated cartridges (for carbonyl compounds). The samples were analyzed using high resolution gas chromatographic separation with Fourier transform infrared/mass spectrometric detection (GC/IRD/ MSD) for qualitative identification and with flame ionization detection (GC/FID) for quantitation of hydrocarbons, and high performance liquid chromatography (HPLC) for identification and quantitation of carbonyl compounds. A custom-designed database management system was used to handle the large data sets generated by these analyses. From the evaluation of canister and Tenax sample stability upon storage, it was found that hydrocarbons in the C8---C12 range seemed to be more stable in the Tenax cartridge than in the canister. The effect of the Nafion® dryer (frequently used for moisture removal prior to cryogenic concentration of the canister samples) was also assessed and it was found to lower the measured concentrations of hydrocarbons collected in the canisters. Comparison of hydrocarbon concentrations found in the Tenax and canister samples allows an assessment of the contribution of semi-volatile hydrocarbons (C10---C20 range derived from Tenax data) to the total non-methane hydrocarbons (C2---C20, derived from canisters and Tenax data). The results of this study show that hydrocarbons in the range of C10---C20 are important components of gas-phase hydrocarbons emitted from heavy-duty diesel vehicles (they account for approximately half of the total gas-phase non-methane hydrocarbon emission rates) and hence that solid adsorbent sampling should be used in addition to canister sampling in measurements of motor vehicle emissions.