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

Eric S Edgerton; Yu-Mei Hsu; Emily M White; Mark E Fenn; Matthew S Landis

doi:10.1016/j.scitotenv.2019.134864

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

Sci Total Environ. 2020 Mar 1:706:134864. doi: 10.1016/j.scitotenv.2019.134864. Epub 2019 Nov 18.

Authors

Eric S Edgerton¹, Yu-Mei Hsu², Emily M White³, Mark E Fenn⁴, Matthew S Landis⁵

Affiliations

¹ Atmospheric Research & Analysis, Inc., 410 Midenhall Way, Cary, NC, 27513, USA. Electronic address: eedgerton@atmospheric-research.com.
² Wood Buffalo Environmental Association, 805 Memorial Drive, Fort McMurray, T9K0K4, Canada.
³ Maed Consulting, 151 Harrison Court, Pittsboro, NC, 27312, USA.
⁴ USDA Forest Service, Pacific Southwest Research Station, 4955 Canyon Crest Drive, Riverside, CA, 92507, USA.
⁵ Integrated Atmospheric Solutions, LLC, 1009 Yellow Birch Drive, Cary, NC, 27519, USA. Electronic address: mlandis@atmospheric-solutions.com.

PMID: 31855646
DOI: 10.1016/j.scitotenv.2019.134864

Abstract

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 ~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 PM_2.5 data showed that >80% of SO₄^2- was in the PM_2.5 fraction, while > 60% of Ca²⁺, Mg²⁺, Na⁺ and Cl^- were in the PM_10-2.5 fraction. Ion balances of both PM₁₀ 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 PM₁₀ ions showed peak Ca²⁺ during March-April to November, but peak SO₄^2-, 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 (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.

Keywords: Ammonia; Atmospheric deposition; Base cations; Boreal forest; Nitric acid; Nitrogen; Oil sands; Sulfur.