The three western Canadian provinces (British Columbia, Alberta and Saskatchewan) are responsible for more than 90 % of the 2017 national total fugitive methane (CH4) emissions from the oil and gas sector. Several survey-based previous studies demonstrated that government estimated CH4 emissions from western Canada’s oil and gas sector are significantly underestimated due to large methodological uncertainties. Most of these survey-based studies were conducted for a limited number of days in a small area; scaling up the short-term results over a larger area for the whole year might lead to emission estimation errors. However, accurate quantification is required to inform effective emission reduction policies in Canada. To improve our understanding of CH4 emissions from the oil and gas sector in western Canada, this Ph.D work has addressed the above problem by using a combination of long-term satellite XCH4 data sets (SCIAMACHY and GOSAT; 2003-2017) and NOAA/ESRL aircraft CH4 measurements, as well as GEOS-Chem CH4 simulation (2010-2017). The overall XCH4 enhancement trend was found to be 6.71 ±4.84 %/yr in western Canada during 2009-2017, which is likely influenced by local oil and gas development activities. The oil and gas CH4 emissions estimation using an ensemble of GOSAT XCH4 data products in a mass balance method demonstrated a fluctuating pattern of emissions in these three provinces during 2009-2017, largely due to diminished oil and gas development activities particularly during 2014-2016. The satellite-based estimated oil and gas CH4 emissions in British Columbia and Saskatchewan are higher than the government inventory by ~200 %, but only higher by ~50 % in Alberta. Although the GOSAT products are suitable for quick and reasonably accurate annual CH4 emissions quantification in western Canada, the GOSAT product is limited in its ability to detect monthly emissions, which is required considering the seasonality of CH4 emissions from major sources. Therefore, further studies particularly with TROPOMI is strongly suggested. Furthermore, the GEOS-Chem based numerical experiments identified emissions from major sources such as wetlands and oil and gas sector are spatially overlapped in the oil and gas dominated areas, particularly during summer, suggesting further oil and gas CH4 emission studies should be carefully conducted.
