Ambient concentrations and total deposition of inorganic sulfur, inorganic nitrogen and base cations in the Athabasca Oil Sands Region

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Trace gas, particulate matter and deposition data collected in the Athabasca Oil Sands Region (AOSR) from 2000 to 2017 were evaluated as part of a broad scientific programmatic review. Results showed significant spatial patterns and temporal trends across the region. Concentrations of reactive gases were highest near the center of surface oil sands production operations and decreased towards the edges of the monitoring domain by factors of 8, 20, 4 and 3 for SO 2 , NO 2 , HNO 3 and NH 3 , respectively. 18 of 30 sites showed statistically significant ( p < 0.05) negative trends in SO 2 concentrations suggesting an ~40% decrease since 2000. In contrast, only 2 of 30 sites showed statistically significant temporal trends (1 positive, 1 negative) for NO 2 . NH 3 data showed (i) intermittent wildfire impacts, and (ii) high seasonality, with low concentrations during winter and significantly higher values during the summer. PM 10 measurements were more limited, but also showed significant spatio-temporal variability. Comparison of PM 10 and PM 2.5 data showed that >80% of SO 4 2− was in the PM 2.5 fraction, while > 60% of Ca 2+ , Mg 2+ , Na + and Cl − were in the PM 10-2.5 fraction. Ion balances of both PM 10 and PM 2.5 contained cation excesses at near-field oil sand sites, but PM 2.5 samples at forest health sites >20 km from surface production locations contained anion excesses. Monthly average concentrations of PM 10 ions showed peak Ca 2+ during March-April to November, but peak SO 4 2− , NH 4 + and NO 3 − from November-March. Deposition estimates showed rapid declines as a function of distance to oil sand operations. Estimated total N and total S deposition to forest health monitoring sites ranged from 2.0 to 5.7 kg ha −1 a −1 and 2.1–14.0 kg ha −1 a −1 , respectively. Potential acid input (PAI) ranged from −0.46 to 0.79 keq ha −1 a −1 and was mostly 0.1–0.2 keq ha −1 a −1 throughout the domain, except for two clusters of sites near oil sand operations.