Search

For methane emission reduction strategies in urban areas to be effective, large emitters must be identified. Recent studies in U.S. cities have highlighted the contribution of methane emissions from natural gas distribution networks and end use. We present a methane emission source identification and quantification method for the Greater Toronto Area (GTA), the largest metropolitan area in Canada, using mobile gas monitoring systems. From May 2018 to August 2019, we collected 77 surveys of methane mixing ratios, covering a distance of about 6400 km, and sampled emission plumes from sources such as closed landfills, natural gas compressor stations, and waterways. Our results indicate that inactive landfills emit less than inventory estimates. Despite this discrepancy, we confirm that the waste sector is the largest methane emitter in the GTA. We also report that the frequency of methane leaks from the local distribution system ranges between 4 and 22 leaks per 100 km of roadway in downtown Toronto, which is comparable to the range observed in U.S. cities, which have invested in modern natural gas distribution infrastructure. Last, we find that engineered waterways, whose emissions are currently not reported in inventories, may be a significant source of methane.

Source attribution of natural gas emissions from fossil fuels in New Mexico's San Juan Basin (SJB) is challenging due to source heterogeneity and emissions transience. We demonstrate that ethane (C2H6) to methane (CH4) mixing ratios can identify and separate sources over different scales using various measurement techniques. We report simultaneous CH4and C2H6observations near a coal mine vent and oil and gas (O&G) emission sources using ground‐based in situ measurements in 2020/2021. During these campaigns, we observed a stable coal vent C2H6:CH4ratio of 1.28% ± 0.11%, discernibly different than nearby O&G source ratios ranging from 0.9% to 16.8%. We analyze airborne observations of the SJB taken in 2014/2015 that exhibit similar coal vent ratios and further show the region's heterogeneity. We identify episodic O&G sources, including a gas plant source detected in 2014/2015 that is absent in our 2020/2021 data. We examine total column observations of C2H6and CH4made in 2013 with a solar spectrometer and find a C2H6:CH4ratio of 1.3% ± 0.4% for the coal vent. The stable and unique coal vent ratio relative to other O&G sources in the region is used to demonstrate that consistent attribution is possible using various measurement methods at multiple scales across many years. Finally, we demonstrate that using C2H6as a proxy for fossil CH4inversions can inform detailed basin‐scale inversions, provided we understand source specific changes in the C2H6:CH4ratio like we report in the SJB. Oil, gas, and coal production processes are known to emit methane, a potent greenhouse gas, and other hydrocarbon air pollutants. Attributing these emissions to specific anthropogenic fossil sources is challenging in the vast and variable infrastructure. Ethane is often co‐emitted with methane and the ratio of ethane to methane in emission sources varies significantly with source types. By measuring this ratio with high sensitivity and accuracy, we can “fingerprint” gas sources by their unique ratio. We report simultaneous measurements of ethane and methane, and an empirical analysis of the ratio to demonstrate source specific attribution. Our varied measurement techniques spanning spatial scales (near‐source ground, airborne, and remote sensing) were used to sample sources in New Mexico's San Juan basin over 8 years. Despite a diverse and changing emissions environment, ethane to methane ratios were successfully used to identify and apportion several sources across scales in space and time. Specifically, our measurements show consistent and stable ethane to methane ratios from a large coal vent source in the study region. Our findings inform efforts seeking to characterize and quantify gas emissions in fossil extraction regions using multi‐scale data from diverse instruments. Multiple measurement techniques across spatiotemporal scales show consistent and stable ethane:methane ratios from a coal vent shaftEthane:methane ratios are a valuable tool for source apportionment, plume separation, and oil and gas basin emissions characterizationA large gas plant source was identified in 2015 but abated in 2021 showing change with time and monitoring Multiple measurement techniques across spatiotemporal scales show consistent and stable ethane:methane ratios from a coal vent shaft Ethane:methane ratios are a valuable tool for source apportionment, plume separation, and oil and gas basin emissions characterization A large gas plant source was identified in 2015 but abated in 2021 showing change with time and monitoring

The dairy industry in the San Joaquin Valley (SJV) is one of California’s largest methane (CH4) sources. Reducing dairy emissions is a priority for the state’s climate change plans. Observations of current dairy CH4emissions are key to monitoring actions taken toward this goal. To help support this, we present new ground‐based measurements of atmospheric column‐averaged CH4mixing ratio (XCH4) gradients across a group of 600 dairies in the central SJV using EM27/SUN solar spectrometers. We used measurements from the 2019 summer and 2020 winter seasons for a top‐down emission inversion based on the WRF‐STILT model. Our top‐down estimates of the region’s dairy emissions range from 90% to 183% of the current CALGEM inventory’s emissions of 277 Gg/yr. In contrast to the strong temperature dependence found by earlier dairy CH4emission studies, we also find that our top‐down emissions during the winter measurement days are comparable to the summer measurement days, possibly due to seasonal changes in dairy management practices and meteorological conditions. Furthermore, we find significant interday variability in our measurements and find that our emission estimates overlap with earlier top‐down studies and bottom‐up inventories in this region. Our study demonstrates how analysis of ground‐based remotely sensed CH4gradient observations can help improve our understanding of CH4sources at scales relevant to mitigation policy. It also reflects the need for long‐term monitoring of CH4emissions in the region and at individual facilities to better understand their emissions. We present total column measurements of the San Joaquin Valley's dairy methane emissions using EM27/SUN spectrometers over 6 measurement daysTop‐down emission estimates from this data show interday variability and overlap with published San Joaquin Valley emission estimatesOur measurements' winter emissions are comparable to summer emissions in contrast to patterns expected due to temperature We present total column measurements of the San Joaquin Valley's dairy methane emissions using EM27/SUN spectrometers over 6 measurement days Top‐down emission estimates from this data show interday variability and overlap with published San Joaquin Valley emission estimates Our measurements' winter emissions are comparable to summer emissions in contrast to patterns expected due to temperature