Please use this identifier to cite or link to this item: http://hdl.handle.net/2122/10758
Authors: Etiope, Giuseppe* 
Doezema, Lambert* 
Pacheco, C.* 
Title: Emission of Methane and Heavier Alkanes From the La Brea Tar Pits Seepage Area, Los Angeles
Issue Date: 2017
Series/Report no.: /122 (2017)
DOI: 10.1002/2017JD027675
URI: http://hdl.handle.net/2122/10758
Abstract: Natural hydrocarbon (oil and gas) seeps are widespread in Los Angeles, California, due to gas migration, along faults, from numerous subsurface petroleum fields. These seeps may represent important natural contributors of methane (CH4) and heavier alkanes (C2-C4) to the atmosphere, in addition to anthropogenic fossil fuel and biogenic sources. We measured the CH4 flux by closed-chamber method from the La Brea Tar Pits park (0.1 km2), one of the largest seepage sites in Los Angeles. The gas seepage occurs throughout the park, not only from visible oil-asphalt seeps but also diffusely from the soil, affecting grass physiology. About 500 kg CH4 d-1 is emitted from the park, especially along a belt of enhanced degassing that corresponds to the 6th Street Fault. Additional emissions are from bubble plumes in the lake within the park (order of 102–103 kg d-1) and at the intersection of Wilshire Boulevard and Curson Avenue (>130 kg d-1), along the same fault. The investigated area has the highest natural gas flux measured thus far for any onshore seepage zone in the USA. Gas migration, oil biodegradation, and secondary methanogenesis altered the molecular composition of the original gas accumulated in the Salt Lake Oil Field (>300 m deep), leading to high C1/C2+ and i-butane/n-butane ratios. These molecular alterations can be important tracers of natural seepage and should be considered in the atmospheric modeling of the relative contribution of fossil fuel (anthropogenic fugitive emission and natural geologic sources) versus biogenic sources of methane, on local and global scales.
Appears in Collections:Papers Published / Papers in press

Files in This Item:
File Description SizeFormat 
Etiope et al 2017 La Brea .pdf1.87 MBAdobe PDFView/Open
Show full item record

Page view(s)

30
Last Week
1
Last month
4
checked on Nov 15, 2018

Download(s)

6
checked on Nov 15, 2018

Google ScholarTM

Check

Altmetric