Atmospheric wet deposition of mercury to the Athabasca Oil Sands Region, Alberta, Canada

Abstract

Event-based wet deposition of mercury, Hg, was collected in a study from 2010 to 2012 at the AMS 6 site 30 km from the nearest oil sands industrial facilities in Fort McMurray, AB, Canada. For the entire study period (21 months), volume weighted mean, VWM, concentration was 11.2 ng L−1 while total Hg wet deposition was 2.3 μg m−2. Mercury enrichment factors ranged from 10 to 5419 in rainfall, 45–599 in mixed precipitation and 73–266 in snowfall samples. This suggests that emissions from local anthropogenic sources of mercury were available for scavenging especially in rainfall. During a 3-day period in June 2011, there was a 5 to 24-fold increase in mercury enrichment in rainfall samples compared to previous samples. Meteorological analysis during this period provides evidence that mercury containing emissions in smoke from forest fires were transported by winds and subsequently deposited in rainfall received at the sampling site thereby causing enrichment. The magnitude of mercury wet deposition at the AMS 6 site was one of the lowest observed fluxes compared to measurements made elsewhere in the United States and Canada, most likely limited by the low precipitation depths that occurred at this semi-arid location. The reduced wet deposition suggests that mercury dry deposition may be significant in the Athabasca Oil Sands Region, AOSR, and should be addressed in future studies.