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Spatial patterns and source attribution of urban methane in the Los Angeles Basin

Hopkins, Francesca M. and Kort, Eric A. and Bush, Susan E. and Ehleringer, James R. and Lai, Chun-Ta and Blake, Donald R. and Randerson, James T. (2016) Spatial patterns and source attribution of urban methane in the Los Angeles Basin. Journal of Geophysical Research. Atmospheres, 121 (5). pp. 2490-2507. ISSN 2169-897X. http://resolver.caltech.edu/CaltechAUTHORS:20160317-132327182

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Abstract

Urban areas are increasingly recognized as a globally important source of methane to the atmosphere; however, the location of methane sources and relative contributions of source sectors are not well known. Recent atmospheric measurements in Los Angeles, California, USA, show that more than a third of the city's methane emissions are unaccounted for in inventories and suggest that fugitive fossil emissions are the unknown source. We made on-road measurements to quantify fine-scale structure of methane and a suite of complementary trace gases across the Los Angeles Basin in June 2013. Enhanced methane levels were observed across the basin but were unevenly distributed in space. We identified 213 methane hot spots from unknown emission sources. We made direct measurements of ethane to methane (C_2H_6/CH_4) ratios of known methane emission sources in the region, including cattle, geologic seeps, landfills, and compressed natural gas fueling stations, and used these ratios to determine the contribution of biogenic and fossil methane sources to unknown hot spots and to local urban background air. We found that 75% of hot spots were of fossil origin, 20% were biogenic, and 5% of indeterminate source. In regionally integrated air, we observed a wider range of C_2H_6/CH_4 values than observed previously. Fossil fuel sources accounted for 58–65% of methane emissions, with the range depending on the assumed C_2H_6/CH_4 ratio of source end-members and model structure. These surveys demonstrated the prevalence of fugitive methane emissions across the Los Angeles urban landscape and suggested that uninventoried methane sources were widely distributed and primarily of fossil origin.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1002/2015JD024429DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/2015JD024429/abstractPublisherArticle
ORCID:
AuthorORCID
Randerson, James T.0000-0001-6559-7387
Additional Information:© 2016 American Geophysical Union. Received 3 NOV 2015. Accepted 17 FEB 2016. Accepted article online 20 FEB 2016. Original geolocated, time-stamped trace gas measurements made by mobile laboratory are provided as Data Set S1. This research is funded by the U.S. Department of Energy's Office of Science (BER) under grant DE-SC0005266. This work was supported in part by the W. M. Keck Institute for Space Studies. We thank Valerie Carranza, Joshua Miu, Mariela Ruacho, Kristal Verhulst, Josette Marrero, and Tianyang Zhu for help with field work and Simone Meinardi for help in the laboratory.
Group:Keck Institute for Space Studies
Funders:
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0005266
Keck Institute for Space Studies (KISS)UNSPECIFIED
Subject Keywords:methane; ethane; emissions; fugitive; apportionment
Record Number:CaltechAUTHORS:20160317-132327182
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20160317-132327182
Official Citation:Hopkins, F. M., E. A. Kort, S. E. Bush, J. R. Ehleringer, C.-T. Lai, D. R. Blake, and J. T. Randerson (2016), Spatial patterns and source attribution of urban methane in the Los Angeles Basin, J. Geophys. Res. Atmos., 121, 2490–2507, doi:10.1002/2015JD024429.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:65441
Collection:CaltechAUTHORS
Deposited By: Colette Connor
Deposited On:17 Mar 2016 21:13
Last Modified:03 Oct 2016 17:22

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