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

Abstract

The Athabasca Oil Sands Region (AOSR) in northern Alberta, Canada is a significant source of particulate elements, which may cause negative effects on human and ecosystem health. This study simulates the transport and deposition of eight elements (Al, Ca, Fe, K, Mn, Si, Ti, and Zn) in the AOSR during 2016-2017 using WRF-Chem with a recently developed regional-scale emission database of elements as model input. Point and area emissions of the elements were gridded in the model domain, with stack emissions also considering the plume rise. The model-measurement differences in annual concentrations of the sum of the eight elements were 23% at AMS1, 25% at AMS17, and -56% at AMS18. Modeled annual average concentrations and atmospheric deposition of individual elements ranged from 0.016 to 2.67 μg m^-3 (the sum total of 5.98 μg m^-3) and from 2.62 to 385 mg m^-2yr^-1 (862 mg m^-2yr^-1), respectively, in the central industrial area of the AOSR. The concentration and deposition decreased rapidly with distance from the center industrial area, e.g., by three orders of magnitude in areas 150 km away. Adding the three sites together, modeled total concentrations of the eight elements were 110% higher during the cold season and 29% lower during the warm season than the measured values, noting that constant emission rates were used throughout the years of 2016-2017. Two model sensitivity tests were conducted, with the first one using seasonally varying emissions and the second one replacing the default dry and wet deposition schemes in WRF-Chem with different ones found in literature, to demonstrate the magnitudesof the uncertainties in the model simulated ambient concentrations and atmospheric deposition of particulate elements and major causing factors of the uncertainties.