Reactive oxygen species, environmentally persistent free radicals, and oxidative potential of outdoor and indoor particulate matter in Wintertime Fairbanks, Alaska

Sub-arctic cities can face episodes of high air pollution during wintertime that can lead to human exposure to high concentrations of particulate matter. During the ALPACA campaign in Fairbanks, Alaska in January–February 2022, we conducted sampling of outdoor fine particulate matter (PM_2.5) using a high-volume sampler and indoor PM using a size-segregated cascade impactor in a house during activities including cooking and residential heating using a pellet stove. We aimed to characterize health-related properties of outdoor and indoor PM by measuring environmentally persistent free radicals (EPFRs) and reactive oxygen species (ROS) using electron paramagnetic resonance (EPR) spectroscopy. We also quantified PM oxidative potential (OP) using the dithiothreitol (OP-DTT) and OH (OP-OH) assays. We found that outdoor PM generates •OH (67%) and carbon-centered radicals (33%), while indoor PM predominantly forms •OH (93%) in water. Indoor activities of pellet stove burning generated substantial amounts of EPFRs in submicron PM. Both indoor and outdoor ROS exhibit little correlations with OP-DTT. Outdoor •OH correlates well with water-soluble iron (R² = 0.51), indicating the role of Fenton(-like) reactions in generating •OH in the aqueous phase. Both OP-OH and the modeled OH production rate in lung lining fluid correlate strongly with EPFRs, indicating that EPFRs are redox active to generate •OH. We also observe that EPFRs show a weak correlation with measured •OH formation in water but with a much stronger correlation with measured •OH in surrogate lung fluid, emphasizing the importance of lung antioxidants for redox cycling of EPFRs in the generation of •OH.