Abstract
Abstract. Conventional passive air samplers (PAS) and passive dry deposition samplers (PAS-DD) were deployed along a 90 km south–north transect at five sites in the Athabasca oil sands region (AOSR) during October to November 2015. The purpose was to compare and characterize the performance of the two passive sampling methods for targeted compounds across a range of site types. Samples were analyzed for polycyclic aromatic compounds (PACs), nitrated polycyclic aromatic hydrocarbons (NPAHs), and oxygenated PAHs (OPAHs). ΣPAC and ΣNPAH concentrations were highest in PAS and PAS-DD samplers at site AMS5, which is the closest sampling site to surface mining and upgrading facilities. The OPAHs were elevated at site AMS6, which is located in the town of Fort McMurray, approximately 30 km south of the main mining area. PAS-DD was enriched relative to PAS in particle-associated target chemicals, which is consistent with the relatively more open design of PAS-DD intended to capture particle-phase (and gas-phase) deposition. Petroleum coke (petcoke) (i.e., the carbonaceous byproduct of bitumen upgrading) and oil sands ore (i.e., the material mined in open-pit mines from which bitumen is extracted) were assessed for their potential to be a source of PACs to air in the oil sands region. The ore samples contained ∼ 8 times and ∼ 40 times higher ΣPACs concentrations (dry weight basis) than delayed and fluid petcoke, respectively. The residue analysis of ore and petcoke samples also revealed that the chemical 4-nitrobiphenyl (4-NBP) can be used to track gas-phase emissions to air. A comparison of chemical residues in ore, petcoke, and air samples revealed that the ore is likely a major contributor to volatile PACs present in air and that both ore and petcoke are contributing to the particle-associated PACs in air near open-pit mining areas. The contribution of petcoke particles in passive air samples was also confirmed qualitatively using scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS).
Highlights
Application of passive air sampling techniques has become widespread due to their simplicity, convenience, and costeffectiveness
A recent study demonstrated that the Global Atmospheric Passive Sampling (GAPS)-type polyurethane foam (PUF)-passive air samplers (PAS) was capable of accumulating particles, ranging in size from 250 to 4140 nm, with no discrimination compared to conventional PS-1-type active air samplers (Markovic et al, 2015)
The PAS and passive dry deposition samplers (PAS-DD) samples exhibited similar relative polycyclic aromatic compounds (PACs) compositions, with C1 phenanthrenes and anthracenes (C1PHEs+ANTs) and PHE being the most abundant alk-polycyclic aromatic hydrocarbons (PAHs) and parent PAH, respectively (Fig. S2). For both PAS and PAS-DD samplers, the PAC chemical compositions were dominated by the 2–3-ring PAHs and 2–3-ring alk-PAHs, which accounted for 77–87 % of the sum of all target compounds (Fig. 2)
Summary
Application of passive air sampling techniques has become widespread due to their simplicity, convenience, and costeffectiveness. Coarse particles (aerodynamic diameter > 10 μm) are excluded from collection since the overlapping double-dome design of the PUFPAS does not allow direct flow of bulk air through the sampler (Thomas et al, 2006). A prototype passive dry deposition sampler (PAS-DD) was introduced in our recent study to assess dry deposition of polycyclic aromatic hydrocarbons (PAHs) and related compounds (Eng et al, 2013). The design of PAS-DD, which incorporates a PUF disk as the collection substrate, positioned between two open parallel flat plates that are shielded above, allows for dry particle deposition from bulk air as well as dry gas-phase deposition (Fig. S1)
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