Quantifying the Loss of Processed Natural Gas Within California's South Coast Air Basin Using Long-term Measurements of Ethane and Methane

Abstract

<p><strong>Abstract.</strong> California's South Coast Air Basin (SoCAB) is a region in which the top-down methane emissions are underestimated by the bottom-up inventories. To provide insight into the sources of the discrepancy, we analyse a record of atmospheric trace gas total column abundances in the SoCAB starting in the late 1980s. The gases measured include ethane and methane and provide insight into the sources of the excess methane found in the SoCAB. The early few years of the record show a rapid decline in ethane emissions at a much faster rate than decreasing vehicle exhaust or natural gas and crude oil production can explain. Between 2010 and 2015, ethane emissions have grown gradually from 13 ± 4.5 Gg · yr<sup>−1</sup> to 25.8 ± 3.9 Gg · yr<sup>−1</sup>, which is in contrast to the steady production of natural gas liquids over that time. Our methane emissions record begins in 2012 and shows an increase between 2012 and 2015 from 380 ± 78 Gg · yr<sup>−1</sup> to 448 ± 91 Gg · yr<sup>−1</sup>. Since 2012, ethane to methane ratios in the natural gas withdrawn from a storage facility within the SoCAB have been increasing; these ratios are tracked in our atmospheric measurements with about half of the rate of increase. From this, we infer that about half of the excess methane in the SoCAB between 2012–2015 is attributable to losses from the natural gas infrastructure.</p>

Anthropogenic Methane Emission and Its Partitioning for the Yangtze River Delta Region of China

“…Despite the disproportionate role that cities play in the global carbon cycle, large uncertainties persist at the regional to city scales (Mitchell et al, ; Wu et al, ). Improved knowledge of CH 4 emissions from urban areas is of high priority in improving our understanding of the global CH 4 cycle and for developing practical mitigation strategies (Hopkins et al, ; Townsend‐Small et al, ; Wunch et al, ).…”

“…Based on the theory that “excess” GHG gas (i.e., enhancement) above “background” values can reflect the influence of both local emissions and meteorological conditions, top‐down atmospheric techniques combine high‐precision mixing ratio observations and transport modeling to constrain bottom‐up emission estimates from urban regions (Mitchell et al, ; Salmon et al, ; Sargent et al, ). Townsend‐Small et al () found that fugitive emissions of CH 4 in California, USA, were underestimated by more than ~50% based on isotopic constraints and the difference between their top‐down estimates compared with with a priori inventories for California (Hopkins et al, ; Wong et al, ; Wunch et al, ). By applying a Bayesian inversion method, Chen et al () also reported that CH 4 emissions from oil/gas sources and livestock were underestimated by 1.3 and 1.8 times, respectively, for the Upper Midwestern United States.…”

Emissions and topographic effects on column CO2 () variations, with a focus on the Southern California Megacity

“…The SoCAB has ∼17 million inhabitants sprawled over four counties (Los Angeles, Orange, San Bernardino, and Riverside) and more than 160 cities. SoCAB emissions have been estimated to be on order of 167 Tg CO 2 yr −1 [ Wunch et al , ] which is ∼3.2% of fossil fuel and cement production CO 2 emissions from the United States or approximately 0.4% of the total global anthropogenic CO 2 emissions.…”

“…Column‐averaged DMFs (e.g., ) have been suggested to be important tools for Measurement, Reporting, and Verifying (MRV) of emissions from urban areas [ Kort et al , ; McKain et al , ; Keppel‐Aleks et al , ; Hase et al , ; Wunch et al , ]. is measured long term with remote sensing instruments (e.g., by satellites or ground‐based solar viewing spectrometers).…”

Methane emissions from groundwater pumping in the USA

“…20,21 Annual emissions of methane since 2007 in the SoCAB have been~0.413 ± 0.086 Tg/a methane and~0.023 Tg/a ethane. 21,22 Methane emissions in the United States for various sectors including agriculture, energy, waste, industrial processes, land use change and forestry have been estimated as a total flux of~29.03 Tg of methane 23 in the year 2000. Global emissions of methane are estimated at~275 Tg/ a of methane in 2010.…”