THE COMPOSITION AND CONCENTRATION OF HYDROCARBONS IN THE RANGE OF C2 TO C18 IN DOWNTOWN LOS-ANGELES, CA

Ambient air samples were collected in the downtown Los Angeles (Califo rnia) area and analyzed for non-methane hydrocarbons in the range of C 2 to C18. Two daily samples were collected, using stainless steel cani sters and Tenax-TA solid adsorbent cartridges, over four days in Augus t 1991. The samples were analyzed using high resolution gas chromatogr aphic separation and Fourier transform infrared/mass spectrometric det ection (GC/IRD/MSD) or flame ionization detection (FID) of individual hydrocarbons. The comparison of hydrocarbon concentrations found in th e Tenax and canister samples and the assessment of the contribution of semivolatile hydrocarbons (C10-C18 range) to the sum of non-methane h ydrocarbons (C2-C10 or C2-C12), as measured by the canister method, is presented. This contribution ranges from approximately 7% to 15% (for C10-C18 range) and approximately 3% to 8% (for C12-C18 range). The se mivolatile hydrocarbons also contribute approximately 16% to the total ozone forming potential of non-methane hydrocarbons.