Research Projects

Nonmethane hydrocarbons (NMHC) in ambient air are routinely analyzed for C2 to C10 species. The significance of the > C10 relative to the C2 to C10 and C2 to C12 hydrocarbons was assessed by a study conducted during the summer of 1991 at three locations in California, with different predominant emission sources. The Caldecott Tunnel, located in the San Francisco area, was selected as a site dominated by motor vehicle emissions. The remaining sampling sites were: Los Angeles as a typical urban site, and Oildale as a site dominated by oil production. Whole air samples, analyzed for C2 through C12 hydrocarbons, were collected using the stainless steel canisters. Semi-Volatile hydrocarbons, in the range of C8 to C18, were collected using Tenax-TA solid adsorbent. The samples were analyzed using high resolution gas chromatographic separation and Fourier transform infrared / mass spectrometric detection (GC/IRD/MSD) or flame ionization detection (FID) of individual hydrocarbons. The comparison of hydrocarbon concentrations found in the Tenax and canister samples and the assessment of the levels of semivolatile hydrocarbons (C10-C18 range) relative to total non-methane hydrocarbons (C2-C10 or C2-C12), as measured by the canister method, is presented. The results showed that the percent contribution of SVHC to TNMHC ranged from ~1 to ~18% depending on the carbon number arbitrarily selected as a starting point of SVHC range. If the hydrocarbons are quantified only up to C10 from canister samples, the percent contribution of C10 to C18 SVHC, ranged from ~6 to ~18%. The contribution of SVHC in the range of C12 to C18, was considerably lower and ranged from ~1 to ~7%.