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Open Access Publications from the University of California

Scholarly Works (2 results)

  • Thesis
  • Peer Reviewed
UC Irvine Electronic Theses and Dissertations (2018)

Short lived greenhouse gases are an immediate target for reductions in climate policy planning. To understand to what extent legislation to limit greenhouse gas emissions is working, monitoring projects are necessary. In this work, whole air samples were collected downwind of the Los Angeles megacity over the course of two years between June 2014 and May 2016. Samples were analyzed via gas chromatography instruments to quantify over 70 volatile organic compounds with limits of detection on the single part per trillion level.

Unlike larger hydrocarbons, the daytime average mixing ratio for both methane and ethane did not decrease in the region since a previous study in 2007 suggestive of continued natural gas leakage. Using monthly ethane to methane enhancement ratios and natural gas composition of gas delivered to the region showed that 72 ± 16% of all excess methane emitted in the SoCAB was due to natural gas leakage. This result is significantly higher than the fraction due to natural gas in previous bottom-up inventories in the region.

Positive matrix factorization was applied to the data set to aid in apportionment of hydrocarbons to various sources in the region. A seven factor result was obtained in which natural gas, oil and gas refining, biogenic, industrial sources, BTEX, gasoline liquids and tailpipe emissions were matched to source profiles. Via this analysis, 59% (57-65%) of the methane seen in the SOCAB was due to the leakage of unburned natural gas. This agrees well with the result obtained using the composition of delivered gas and two recent studies of the region using other data sets.

Finally, several classes of refrigerants which are potent greenhouse gases were studied. The emission of banned chlorofluorocarbons was noted to have completely stopped in the region. Hydrofluorochlorocarbons are currently being phased out and so emissions estimates were calculated and compared to older data sets to show that regulations are working to limit their emission. HCFC-142b emissions were noted to have dramatically stopped during the sampling period as the result of a phase down rule that went into place on January 1, 2015.

    Cover page: Characterization and Source Apportionment of Greenhouse Gas Emissions in the Los Angeles Megacity
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2016)
    Methane emissions inventories for Southern California's South Coast Air Basin (SoCAB) have underestimated emissions from atmospheric measurements. To provide insight into the sources of the discrepancy, we analyze records of atmospheric trace gas total column abundances in the SoCAB starting in the late 1980s to produce annual estimates of the ethane emissions from 1989 to 2015 and methane emissions from 2007 to 2015. The first decade of measurements shows a rapid decline in ethane emissions coincident with decreasing natural gas and crude oil production in the basin. Between 2010 and 2015, however, ethane emissions have grown gradually from about 13±5 to about 23±3 Gg yr-1, despite the steady production of natural gas and oil over that time period. The methane emissions record begins with 1 year of measurements in 2007 and continuous measurements from 2011 to 2016 and shows little trend over time, with an average emission rate of 413±86 Gg yr-1. Since 2012, ethane to methane ratios in the natural gas withdrawn from a storage facility within the SoCAB have been increasing by 0.62±0.05%yr-1, consistent with the ratios measured in the delivered gas. Our atmospheric measurements also show an increase in these ratios but with a slope of 0.36±0.08%yr-1, or 58±13% of the slope calculated from the withdrawn gas. From this, we infer that more than half of the excess methane in the SoCAB between 2012 and 2015 is attributable to losses from the natural gas infrastructure.
      Cover page: Quantifying the loss of processed natural gas within California's South Coast Air Basin using long-term measurements of ethane and methaneCreative Commons 'BY' version 4.0 license
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