Quantifying sources of methane using light alkanes in the Los Angeles basin, California

Abstract

[1] Methane (CH 4 ), carbon dioxide (CO 2 ), carbon monoxide (CO), and C 2 -C 5 alkanes were measured throughout the Los Angeles (L.A.) basin in May and June 2010. We use these data to show that the emission ratios of CH 4 /CO and CH 4 /CO 2 in the L.A. basin are larger than expected from population-apportioned bottom-up state inventories, consistent with previously published work. We use experimentally determined CH 4 /CO and CH 4 /CO 2 emission ratios in combination with annual State of California CO and CO 2 inventories to derive a yearly emission rate of CH 4 to the L.A. basin. We further use the airborne measurements to directly derive CH 4 emission rates from dairy operations in Chino, and from the two largest landfills in the L.A. basin, and show these sources are accurately represented in the California Air Resources Board greenhouse gas inventory for CH 4 . We then use measurements of C 2 -C 5 alkanes to quantify the relative contribution of other CH 4 sources in the L.A. basin, with results differing from those of previous studies. The atmospheric data are consistent with the majority of CH 4 emissions in the region coming from fugitive losses from natural gas in pipelines and urban distribution systems and/or geologic seeps, as well as landfills and dairies. The local oil and gas industry also provides a significant source of CH 4 in the area. The addition of CH 4 emissions from natural gas pipelines and urban distribution systems and/or geologic seeps and from the local oil and gas industry is sufficient to account for the differences between the top-down and bottom-up CH 4 inventories identified in previously published work.

Methane emissions from natural gas infrastructure and use in the urban region of Boston, Massachusetts

“…Two recent studies in Los Angeles covering ∼2 mo provide the only previous atmosphere-based ("top-down") estimates of emissions from NG in an urban area, 1-2% (0.7-3% when accounting for the error ranges) of total NG consumed in the basin (10,11). However, attribution of CH 4 emissions to pipeline gas in Los Angeles is complicated by the presence of current and abandoned oil and gas wells, refinery operations, and natural CH 4 seeps, in addition to NG consumption.…”

“…Elevated CH 4 concentrations in urban environments have been documented around the world for decades (7) (SI Appendix, Table S1) and attributed to a variety of anthropogenic source types. Recent studies of urbanized regions in California, using diverse atmospheric observing and modeling approaches, consistently found that CH 4 emission rates were larger than those estimated by regional bottom-up inventories (8)(9)(10)(11)(12). In Boston, elevated CH 4 concentrations have been observed at street level and attributed to >3,000 NG pipeline leaks from antiquated infrastructure (13), but associated CH 4 emission rates were not quantitatively assessed.…”

Constraining sector-specific CO<sub>2</sub> and CH<sub>4</sub> emissions in the US

“…Other CH 4 emitters, including agriculture, landfills, and wetlands, do not emit higher-order alkanes in substantial amounts. For example, Peischl et al (2013) estimate that natural gas leaks account for 90 % of all ethane emissions in the Los Angeles metro region. If one has an estimate of ethane emissions and an estimate of the ethane content of natural gas, then one could estimate CH 4 emissions from oil and gas infrastructure.…”

Four-dimensional variational inversion of black carbon emissions during ARCTAS-CARB with WRFDA-Chem

“…Brioude et al (2013) constrained CO, NO x , and CO 2 , and Cui et al (2015) constrained CH 4 ; both applied a Lagrangian particle dispersion model (LPDM). Peischl et al (2013) constrained CH 4 using a mass balance approach and light alkane signatures from multiple sectors. LPDM benefits from being able to resolve sources on as fine of a grid resolution as is used in the underlying model.…”