Macroseepage of Light Alkanes at La Brea Tar Pits in Los Angeles
Authors:Roger Baril, Paul Contreras
Mentor:Lambert Doezema, Associate Professor of Chemistry, Loyola Marymount University
Macroseepage of light hydrocarbons were measured over seeps at the La Brea Tar Pits in Los Angeles, California. The macroseepage of the light alkanes was measured using aluminum flux chambers with 2 L stainless steel canisters and quantified with gas chromatography using flame ionization detectors (GC-FID). Flux was determined by first taking a reference sample of ambient air at the time of deployment of the flux chamber and using the reference as a background concentration. The flux chambers collected hydrocarbon seepage over ten minute time intervals at several locations within the La Brea Tar Pits. Samples taken over tar seeps exhibited high flux rates with an estimated hourly total light alkane (C2-C5) flux of more than 300 mg per square meter. A maximum hourly flux of more than 1 g per square meter was observed for methane. The methane to ethane ratio of fluxes was higher than ratios associated with typical oil/natural gas signatures. Macroseepage rates appear high enough to be an important local source of light alkanes in Los Angeles.