Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The rapidly expanding and energy-intensive production from the Canadian oil sands, one of the largest oil reserves globally, accounts for almost 12 % of Canada's greenhouse gas emissions according to inventories. Developing approaches for evaluating reported methane (<span class="inline-formula">CH<sub>4</sub></span>) emission is crucial for developing effective mitigation policies, but only one study has characterized <span class="inline-formula">CH<sub>4</sub></span> sources in the Athabasca oil sands region (AOSR). We tested the use of <span class="inline-formula"><sup>14</sup>C</span> and <span class="inline-formula"><sup>13</sup>C</span> carbon isotope measurements in ambient <span class="inline-formula">CH<sub>4</sub></span> from the AOSR to estimate source contributions from key regional <span class="inline-formula">CH<sub>4</sub></span> sources: (1) tailings ponds, (2) surface mines and processing facilities, and (3) wetlands. The isotopic signatures of ambient <span class="inline-formula">CH<sub>4</sub></span> indicate that the <span class="inline-formula">CH<sub>4</sub></span> enrichments measured at the site were mainly influenced by fossil <span class="inline-formula">CH<sub>4</sub></span> emissions from surface mining and processing facilities (56 <span class="inline-formula">±</span> 18 %), followed by fossil <span class="inline-formula">CH<sub>4</sub></span> emissions from tailings ponds (34 <span class="inline-formula">±</span> 18 %) and to a lesser extent modern <span class="inline-formula">CH<sub>4</sub></span> emissions from wetlands (10 <span class="inline-formula">±</span> &lt;1 %). Our results confirm the importance of tailings ponds in regional <span class="inline-formula">CH<sub>4</sub></span> emissions and show that this method can successfully distinguish wetland <span class="inline-formula">CH<sub>4</sub></span> emissions. In the future, the isotopic characterization of <span class="inline-formula">CH<sub>4</sub></span> sources and measurements from different seasons and wind directions are needed to provide a better source attribution in the AOSR.

Highlights

  • Methane (CH4) is an important greenhouse gas that has 32 times the global warming potential of carbon dioxide (CO2) on a 100-year timescale, and which contributes to the production of ozone, water vapor, and CO2 in the atmosphere (Myhre et al, 2013; Etminan et al, 2016)

  • Our results confirm the importance of tailings ponds in regional CH4 emissions and show that this method can successfully separate wetland CH4 emissions

  • Based on the previous aircraft source attribution study (Baray et al, 2018), we identified two main CH4 source categories: CH4 emissions related to the mining and processing of bitumen, and tailings ponds CH4 emissions

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Summary

Introduction

Methane (CH4) is an important greenhouse gas that has 32 times the global warming potential (mass basis) of carbon dioxide (CO2) on a 100-year timescale, and which contributes to the production of ozone, water vapor (in the stratosphere), and CO2 in the atmosphere (Myhre et al, 2013; Etminan et al, 2016). Top-down approaches are used to verify inventory-based GHG emission estimates, and aircraft-based top-down estimates in the AOSR 60 have shown that inventories underestimate GHG emissions (Liggio et al, 2019), with an aircraft-based estimate reporting 48% higher CH4 emissions than in the inventories (Baray et al, 2018) These aircraft measurements were limited to a short period of time (summer 2013), and there have not been other studies confirming and updating these findings. We expect to provide 90 a new and practical proof-of-concept method for the long-term monitoring of key CH4 emissions in regions with multiple CH4 sources like the AOSR, which is crucial to developing effective CH4 mitigation policies and, in the specific case study, to fulfill Canada’s goal of reducing CH4 emissions from the oil and gas sector by 40−45 % below 2012 levels by 2025 (Government of Canada, 2016)

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