USING PB ISOTOPE RATIOS OF PARTICULATE MATTER AND LICHENS FROM THE ATHABASCA OIL SANDS REGION IN ALBERTA, CANADA TO QUANTIFY GLOBAL, REGIONAL, AND LOCAL PB SOURCE CONTRIBUTIONS

Ambient air particulate matter (PM) was collected at the Wood Buffalo Environmental Association AMS-1 Fort McKay monitoring station in the Athabasca Oil Sand Region (AOSR) in Alberta, Canada from February 2010 to July 2011. Daily 24-hr duration fine (PM_2.5) and coarse (PM_10-2.5) PM was collected. 100 pairs of fine and coarse PM were selected for lead (Pb) concentration and isotope analysis to determine short term variation in source contributions. Pb isotope and concentration results from 250 epiphytic lichen samples collected from as far as 150 km from surface mining operations in 2008, 2011, and 2014 were also analyzed to examine longer term spatially resolved source contributions. ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb isotope ratios were used in a three-component mixing model to quantify local, regional, and global sources in the PM and lichen data sets. The global source term included seasonal contributions of thorogenic ²⁰⁸Pb from eastern Asia in the PM datasets. Combined results from the PM_10-2.5 and PM_2.5 indicate PM_2.5 contributions from eastern Asia (34%) exceed local sources of PM_2.5 from the AOSR (20%), regional western Canada sources of PM_2.5 (19%), and PM_10-2.5 from fugitive dust including oil sands (14%), tailings (10%), and haul and access roads (3%). The spatially resolved lichen analysis indicate regional sources contribute 46% of the Pb, local sources 32%, and global sources 22% over the 2008-2014 timeframe. Local sources dominate atmospheric deposition to lichens at the proximal sites (0-30 km), and regional and global sources at the distal sites (30-160 km) from the mining operations. The Pb isotope approach was successful in quantifying globally transported Pb to the AOSR despite being within the aerosol footprint of the world’s largest concentration of bitumen mining and upgrading facilities. 47% of the Pb in the PM_2.5 at AMS-1 was attributed to sources from eastern Asia.