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Principal Investigator: Dr. Barbara Zielinska
Desert Research Institute
August 1992
ARB Contract No. A032-130 (Full Report)
ABSTRACT
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%.
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