Assessing the Oxidative Potential of Outdoor PM_2.5 in Wintertime Fairbanks, Alaska

Abstract

The oxidative potential (OP) of outdoor PM 2.5 in wintertime Fairbanks, Alaska, is investigated and compared to those in wintertime Atlanta and Los Angeles. Approximately 40 filter samples collected in January−February 2022 at a Fairbanks residential site were analyzed for OP utilizing dithiothreitol-depletion (OP DTT ) and hydroxylgeneration (OP OH ) assays. The study-average PM 2.5 mass concentration was 12.8 μg/m 3 , with a 1 h average maximum of 89.0 μg/m 3 . Regression analysis, correlations with source tracers, and contrast between cold and warmer events indicated that OP DTT was mainly sensitive to copper, elemental carbon, and organic aerosol from residential wood burning, and OP OH to iron and organic aerosol from vehicles. Despite low photochemically-driven oxidation rates, the water-soluble fraction of OP DTT was unusually high at 77%, mainly from wood burning emissions. In contrast to other locations, the Fairbanks average PM 2.5 mass concentration was higher than Atlanta and Los Angeles, whereas OP DTT in Fairbanks and Atlanta were similar, and Los Angeles had the highest OP DTT and OP OH . Site differences were observed in OP when normalized by both the volume of air sampled and the particle mass concentration, corresponding to exposure and the intrinsic health-related properties of PM 2.5 , respectively. The sensitivity of OP assays to specific aerosol components and sources can provide insights beyond the PM 2.5 mass concentration when assessing air quality.

Indoor–Outdoor Oxidative Potential of PM2.5 in Wintertime Fairbanks, Alaska: Impact of Air Infiltration and Indoor Activities

“…This estimate was in reasonable agreement with the PM measurements using a medium-cost MODULAIR-PM sensor which combines a nephelometer and optical particle counter to measure PM 1 , PM 2.5 , and PM 10 after correcting for humidity (Figure S2, slope 0.91, intercept 1.36 μg/m 3 , r 2 = 0.92). For outdoor PM 2.5 mass estimation, the AMS-measured species were combined with elemental carbon and metals analyzed from the filters, as described in Yang et al (2024) . This estimation showed good agreement with the PM 2.5 mass concentrations measured by the Alaska Department of Environmental Conservation for the U.S. Environmental Protection Agency using a Beta Attenuation Monitor (BAM) at the National Core (NCore) monitoring site (roughly 2.6 km from the house) (slope 1.04, intercept 2.07 μg/m 3 , r 2 = 0.70).…”

“…The infiltration process led to aerosol drying that would result in a reduction in water content due to the significant I/O RH gradient (mean of ΔRH = −65%). This could cause the evaporation of certain water-soluble DTT-responsive species, such as benzoquinone, since the outdoor OP v DTT was largely water-soluble (mean water-soluble to total was 77%) . The I/O ratio of OP v DTT was negatively correlated with outdoor RH ( r = −0.77); a larger I/O ratio of OP v DTT was observed when outdoor RH was lower and closer to the relatively constant indoor RH of about 10%.…”

“…Both volume-normalized (OP v DTT ) and mass-normalized (OP m DTT ) results are discussed. Details of the outdoor OP DTT can be found in Yang et al (2024) …”

“…Most studies on aerosol particle OP have focused on outdoor air, and we have reported on Fairbanks wintertime outdoor OP DTT . Fewer studies have explored OP of indoor particulate matter from indoor-outdoor air exchange , and from various indoor sources .…”

“…The dithiothreitol-depletion (DTT) assay is one of the most commonly used assays and has been linked to adverse effects, including both acute and chronic diseases. − Other OP assays have also been associated with adverse health effects. − OP DTT is most sensitive to certain metals and organic species, such as Cu, Mn, and various aromatic species. − It can be used to provide insight into potential dose (OP normalized by the volume of air, OP v ) and the particle’s intrinsic health-relevant properties (OP normalized by particle mass concentration, OP m ). A more comprehensive assessment of air quality is likely achieved by utilizing several complementary assays that are sensitive to different sources and aerosol species. − …”