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

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 SO2, NO2, HNO3 and NH3, respectively. 18 of 30 sites showed statistically significant (p < 0.05) negative trends in SO2 concentrations suggesting an similar to 40% decrease since 2000. In contrast, only 2 of 30 sites showed statistically significant temporal trends (1 positive, 1 negative) for NO2. NH3 data showed (i) intermittent wildfire impacts, and (ii) high seasonality, with low concentrations during winter and significantly higher values during the summer. PM10 measurements were more limited, but also showed significant spatio-temporal variability. Comparison of PM10 and PM2.5 data showed that >80% of SO42 was in the PM2.5 fraction, while > 60% of Ca2+, Mg2+, Na+ and Cl- were in the PM10-2.5 fraction. Ion balances of both PM10 and PM2.5 contained cation excesses at near-field oil sand sites, but PM2.5 samples at forest health sites >20 km from surface production locations contained anion excesses. Monthly average concentrations of PM10 ions showed peak Ca2+ during March-April to November, but peak SO42, NH4+ and NO3 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 (PAD 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. (C) 2019 The Author(s). Published by Elsevier B.V.