Methane is a powerful greenhouse gas and its emission sources need to be evaluated. During the 2016 NASA Student Airborne Research Program, whole air samples were collected throughout the San Joaquin Valley aboard the NASA DC-8. The area southeast of Fresno was found to have elevated methane concentrations (2320 ± 2 ppbv). Samples from 2009-2015 SARP flights also exhibited elevated methane in this region. To determine the source of methane in this area, thermogenic and biogenic tracers were analyzed. This area exhibited elevated acetonitrile (399 ± 12 pptv) indicating a small contribution from thermogenic methane. Enhanced methanol (8727 ± 2618 pptv), ethanol (1981 ± 594 pptv), dimethyl sulfide (3.3 ± 0.3 pptv), and isoprene (193 ± 6 pptv) were observed and indicate a large contribution from biogenic sources. Methane to ethane ratios were used to determine two distinct sources of methane in this region. It is difficult to define a single source as the cause of the enhancement as it is most likely from a mixture of sources. Research in this region should be continued, as a more thorough analysis using isotopic and radiocarbon signatures could confirm and quantify individual methane contributions from each potential source.

Presentation Slides: Identifying-Methane-Emission-Sources-in-the-San-Joaquin-Valley