Emissions Estimates and Dispersion Modeling of Alkylated Polycyclic Aromatic Hydrocarbons in the Canadian Athabasca Oil Sands Region

Alkylated polycyclic aromatic hydrocarbons (APAH) are important contaminants of crude oil production and exhibit similar toxicity to their parent compounds. This study developed an emission inventory of APAH in a major oil sands development region of Alberta, Canada, and validated the inventory with ambient concentration measurements through dispersion modeling. The initial estimate of the annual emissions of 21 APAH species in this region was 362 tonnes/year in 2010-2012, of which 309 and 53 tonnes/year were in particle-bound and gas-phase APAH, respectively. Fugitive dust from oil sands mining activities is the primary source of particle-bound APAH, emitting 274 tonnes/year. Other major sources of APAH include tailings ponds (20.8), anthropogenic fuel consumption from mine fleet (16.7), local transportation (16.0), local residential and commercial activities (5.7), and controlled agriculture and forest burning (1.6). The group of species with highest emissions was C1-C4 alkylnaphthalenes (53%), followed by C1-C4 alkylphenanthrenes/anthracenes (19%), C1-C4 fluorenes (13%), and C1-C4 fluoranthenes/pyrenes and C1-C4 benz[a]anthracenes/chrysene/triphenylenes (7% each).

CALPUFF dispersion modeling was performed using the APAH emissions as model input. The model-predicted annual average ambient APAH concentrations at 17 monitoring sites were 1-52% (19% on average) lower than the measurements. Inverse dispersion modeling was then applied to adjust APAH emissions higher by 19% for each of the 21 APAH species, which resulted in a revised estimate of APAH emissions to 431 tonnes/year. With the revised emissions as model input, model bias in the predicted ambient concentration was reduced from -19% to -8%. The predicted average particle-bound APAH concentration was about 30 ng/m³ at local measurement sites and 20 ng/m³ at remote sites, while that of gas-phase APAH was about 35 ng/m³ at local sites and 10 ng/m³ at remote sites. The model results showed the highest concentration of APAH near tailings ponds and open mining faces and downwind areas. Spatial distribution of APAH in the AOSR was influenced by emission sources and the wind patterns of the model domain.