| Abstract | Measurement-based estimates of greenhouse gas (GHG) emissions from complex industrial operations are challenging to obtain, but serve as an important, independent check on inventory-reported emissions. Such top–down estimates, while important for oil and gas (O&G) emissions globally, are particularly relevant for Canadian oil sands (OS) operations, which represent the largest O&G contributor to national GHG emissions. We present a multifaceted top–down approach for estimating CO₂ emissions that combines aircraft-measured CO₂/NOₓ emission ratios (ERs) with inventory and satellite-derived NOₓ emissions from Ozone Monitoring Instrument (OMI) and TROPOspheric Ozone Monitoring Instrument (TROPOMI) and apply it to the Athabasca Oil Sands Region (AOSR) in Alberta, Canada. Historical CO₂ emissions were reconstructed for the surface mining region, and average top–down estimates were found to be >65% higher than facility-reported, bottom–up estimates from 2005 to 2020. Higher top–down vs. bottom–up emissions estimates were also consistently obtained for individual surface mining and in situ extraction facilities, which represent a growing category of energy-intensive OS operations. Although the magnitudes of the measured discrepancies vary between facilities, they combine such that the observed reporting gap for total AOSR emissions is ≥(31 ± 8) Mt for each of the last 3 years (2018–2020). This potential underestimation is large and broadly highlights the importance of continued review and refinement of bottom–up estimation methodologies and inventories. The ER method herein offers a powerful approach for upscaling measured facility-level or regional fossil fuel CO₂ emissions by taking advantage of satellite remote sensing observations. |
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