Global observational coverage of oil and gas methane sources with TROPOMI

Abstract

Abstract Satellite observations have been widely used to measure methane (CH4) emissions from the oil and gas (O&G) industry, particularly by revealing previously undocumented, very large emission events and basin-level emission estimates. However, the performance of retrieving CH4 mixing ratios from the short-wave infrared band of passive remote sensing instruments is spatially and temporally varied due to sunlight, earth surface properties, and atmospheric conditions. Thus, the reliability of satellites is also varied. To assess the reliability of passive remote sensing satellite instruments for routine monitoring of CH4 emissions, we investigated the global observational coverage of the TROPOMI (onboard the Sentinel-5P), which has been providing a daily global CH4 mixing ratio since 2017. A 0.1° x 0.1° gridded global map that indicates the average number of days with valid observations from TROPOMI from 2019 to 2021 was generated by following the measurement retrieval quality-assurance threshold (≥0.5). We found TROPOMI had promising observational coverage over dryland regions (maximum: 58.6%) but limited coverage over tropical regions and high latitudes (minimum: 0%). Cloud cover and solar zenith angle were the primary factors at high latitudes, while aerosol optical thickness was the primary factor over dryland regions. To further assess the country-level reliability of satellites for detecting and quantifying CH4 emissions from the O&G sector, we extracted the average annual TROPOMI observational coverage (TOC) over O&G infrastructure for 160 countries. Seven of the top-10 O&G-producing countries had an average annual TOC < 10% (< 36 days per year), which indicates the limited ability to routinely identify large emissions events, track their duration, and quantify emissions rates using inverse modelling. We further assessed the potential performance of the latter by combining TOC and the uncertainties from the global O&G inventory. Results inverse modeling with CH4 measurements from TROPOMI may only be accurate for quantifying emissions from O&G sectors in countries located in dryland and mid-latitude regions. Conclusively, the current passive-sensing satellites have low potential for frequent monitoring of large methane emissions from O&G sectors in countries located in tropical and high latitudes (e.g., Canada, Russia, Brazil, Norway, and Venezuela). Therefore, alternative methods should be considered for routine emissions monitoring in the corresponding regions.