Macroseepage of light alkanes at the La Brea Tar Pits in Los Angeles
Authors:Alicia Marquez, Derek Weber
Mentor:Lambert Doezema, Associate Professor of Chemistry, Loyola Marymount University
Macroseepage of gases in the La Brea Tar Pits in Los Angeles were measured to determine if light hydrocarbons from the tar seeps affect the air quality in the greater LA area and to ascertain the importance of geological seepage as an emission source. Macroseepage refers to natural gas seeps in which there is a visible bubbling of gases. It has been theorized that macroseepage is an underreported global source of methane and light alkanes. In North America, very few studies have been carried out to quantify the amounts of these compounds that are released via macroseepage. Samples were collected in 2 L stainless steel canisters connected to 0.125 m3 aluminum flux chambers which were sealed airtight over the visible seeps. These air samples were analyzed using gas chromatography ovens equipped with flame ionization detectors (GC-FID). By taking more than seventy samples in this manner, the average flux of methane from the tar pits was found to be 8000 ppm (parts per million by volume) m-2 h-1, the average flux of ethane was 130 ppm m-2 h-1 and the average flux of propane was found to be 80 ppm m-2 h-1. These results suggest that emissions from the La Brea Tar Pits do affect Los Angeles air quality and macroseepage of light alkanes could be an underreported global source for light alkanes.