Scavenging ratios of polycyclic aromatic compounds in rain and snow in the Athabasca oil sands region

• Published in: Atmospheric Chemistry and Physics
• Main Authors: L. Zhang, I. Cheng, D. Muir, J.-P. Charland
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2015
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Fort McMurray; Canada; Mackay; Fort MacKay
• Online Access: https://doi.org/10.5194/acp-15-1421-2015; https://doaj.org/article/c860a16d7766427d9bc81ffbf39478b3

The Athabasca oil sands industry in northern Alberta, Canada, is a possible source of polycyclic aromatic compounds (PACs). Monitored PACs, including polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs, and dibenzothiophenes (DBTs), in precipitation and in air at three near-source sites in the Fort MacKay and Fort McMurray area during January 2011 to May 2012, were used to generate a database of scavenging ratios ( W t ) for PACs scavenged by both snow and rain. Higher concentrations in precipitation and air were observed for alkylated PAHs and DBTs compared to the other PACs. The sums of the median precipitation concentrations over the period of data analyzed were 0.48 μ g L −1 for the 18 PAHs, 3.38 μ g L −1 for the 20 alkylated PAHs, and 0.94 μ g L −1 for the 5 DBTs. The sums of the median air concentrations for parent PAHs, alkylated PAHs, and DBTs were 8.37, 67.26, and 11.83 ng m −3 , respectively. Median W t over the measurement period were 6100 – 1.1 × 10 6 from snow scavenging and 350 – 2.3 × 10 5 from rain scavenging depending on the PAC species. Median W t for parent PAHs were within the range of those observed at other urban and suburban locations, but W t for acenaphthylene in snow samples were 2–7 times higher compared to other urban and suburban locations. W t for some individual snow and rain samples exceeded literature values by a factor of 10. W t for benzo( a )pyrene, dibenz( a,h )anthracene, and benzo( g,h,i )perylene in snow samples had reached 10 7 , which is the maximum for PAH snow scavenging ratios reported in the literature. From the analysis of data subsets, W t for particulate-phase dominant PACs were 14–20 times greater than gas-phase dominant PACs in snow samples and 7–20 times greater than gas-phase dominant PACs in rain samples. W t from snow scavenging were ~ 9 times greater than from rain scavenging for particulate-phase dominant PACs and 4–9.6 times greater than from rain scavenging for gas-phase dominant PACs. Gas-particle fractions of each PAC, particle size distributions ...