Temporal and Spatial Trends of Polycyclic Aromatic Compounds in Air across the Athabasca Oil Sands Region Reflect Inputs from Open Pit Mining and Forest Fires

Results of a passive air monitoring study for polycyclic aromatic compounds (PACs) in the Athabasca oil sands region (AOSR) in Alberta, Canada, are reported. Polyurethane foam disk passive air samplers were deployed for consecutive 2-month periods from November 2010 to January 2016 at 15 sites. Samples were analyzed for polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs (alkPAHs), and dibenzothiophene and its alkylated derivatives (DBTs). Concentrations in air were in the ranges of 0.3-43, 0.15-460, and 0.04-130 ng/m(3) for Sigma PAHs, Sigma alkPAHs, and Sigma DBTs, respectively. The increase in the levels of PACs in air at most sites was small but statistically insignificant over this 5-year period, which is consistent with expectations as in situ bitumen extraction techniques have become predominant over open pit mining in the area. Significant increases in PAC levels were observed at a site that is within a few kilometers of open pit mining that expanded over the study period. The 5-year regional trend for PACs in air provides a baseline against which planned future open pit mining projects (e.g., Teck Frontier) can be assessed for impact. Seasonal trends in concentrations in air were observed for more volatile PACs; concentrations in air were higher in winter than in summer. These trends were not observed for less volatile compounds. Two major forest fire episodes from April to July 2011 and during June and July 2015 resulted in greatly elevated levels for PAH and a small subset of alkylated PAHs but not for the majority of alkPAHs and DBTs. Increases in regional PAH concentrations associated with forest fire periods were consistent with estimates based on published emission factors for PAHs for wood combustion. Although forest fires are likely to be an important source of PAH concentrations in air across the AOSR, alkPAHs and DBTs appear to be primarily associated with emissions from oil sands mining operations. Air quality guidelines for alkPAHs and DBTs are still lacking.