Modeling trace elements over Athabasca oil sands region in Alberta, Canada using WRF-Chem

The Athabasca Oil Sands Region (AOSR) in northern Alberta, Canada serves as a significant source of trace elements. In this study, the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) is modified to predict the transport and deposition of eight elements (Al, Ca, Fe, K, Mn, Si, Ti, and Zn) in the AOSR in 2016 and 2017. The model has a good performance on the air temperature, wind at surface, and precipitation. The model-measurement percentage differences in the annual concentrations of the eight elements at three sites are in the range of -6.9% to 76% at AMS1, -48% to 72% at AMS17, and -165% to 5.8% at AMS18. Modeled annual concentrations and atmospheric deposition of individual element range from 0.016 to 2.67 µg m-3 and 2.62 to 385 mg m-2yr-1 in the central region of the oil sands industry, respectively. Modeled element concentrations and deposition show a rapid decline by around three orders of magnitude from the central region to the remote region in a distance of around 150 km. The modeled total concentrations of the eight elements at three sites are overestimated by 82% in the cold season but underestimated by 38% in the warm season.

In the first sensitivity test, the annual emission is reallocated to 30% in the cold season and 70% in the warm season. This leads to a reduction in the bias for the modeled total concentrations of eight elements from 45% to 13% in the cold season and from 45% to 24% in the warm season. In the second sensitivity test, the original dry&wet deposition schemes in WRF-Chem are replaced by other schemes. The modeled annual total dry and wet depositions of all elements are decreased by 56% and increased by 33%, respectively. The total dry&wet deposition is decreased by 31%.