High Oxidative Potential Observed in Secondary Organic Aerosol Derived from Oil Sands Emissions

Oil sands operations in Alberta, Canada, are a large source of secondary organic aerosol (SOA) with unknown health impacts. As a first step in closing this knowledge gap, the oxidative potential (OP), an established metric linking particle exposure to toxicological effects, of oil sands-derived SOA was investigated via OH-initiated oxidation. Experiments used a mixture of gas-phase precursors emitted from oil sands ore that is expected to be representative of mine-face emissions and three relevant single precursors (n-decane, m-xylene, and naphthalene) for comparison. The OP of the formed SOA in all cases was found to increase rapidly at short simulated photochemical ages (<1.5 days), followed by a decrease upon further oxidation (>2.5 days). This was driven by dynamic changes in SOA composition, particularly organic peroxides, quinones, and unsaturated carbonyls. The measured OP of oil sand ore SOA (OP_OS) ranged from 38.0 to 60.3 pmol min^-1 μg^-1 over photochemical ages of 0.4-4.6 days. This range of OP_OS is considerably higher than those reported for other types of aerosol particles typically present in the oil sands region, including the natural background (e.g., α-pinene and isoprene SOA). The results not only provide the first OP measurements of oil sands-derived SOA but also emphasize the importance of accounting for atmospheric aging when evaluating the oxidative potential of SOA.