Indoor-Outdoor Oxidative Potential of PM 2.5 in Wintertime Fairbanks, Alaska: Impact of Air Infiltration and Indoor Activities.

The indoor air quality of a residential home during winter in Fairbanks, Alaska, was investigated and contrasted with outdoor levels. Twenty-four-hour average indoor and outdoor filter samples were collected from January 17 to February 25, 2022, in a residential area with high outdoor PM 2.5 concentrations. The oxidative potential of PM 2.5 was determined using the dithiothreitol-depletion assay (OP DTT ). For the unoccupied house, the background indoor-to-outdoor (I/O) ratio of mass-normalized OP (OP m DTT ), a measure of the intrinsic health-relevant properties of the aerosol, was less than 1 (0.53 ± 0.37), implying a loss of aerosol toxicity as air was transported indoors. This may result from transport and volatility losses driven by the large gradients in temperature (average outdoor temperature of -19°C/average indoor temperature of 21 °C) or relative humidity (average outdoor RH of 78%/average indoor RH of 11%), or both. Various indoor activities, including pellet stove use, simple cooking experiments, incense burning, and mixtures of these activities, were conducted. The experiments produced PM 2.5 with a highly variable OP m DTT . PM 2.5 from cooking emissions had the lowest OP values, while pellet stove PM 2.5 had the highest. Correlations between volume-normalized OP DTT (OP v DTT ), relevant to exposure, and indoor PM 2.5 mass concentration during experiments were much lower compared to those in outdoor environments. This suggests that mass concentration alone can be a poor indicator of possible adverse effects of various indoor emissions. These findings highlight the importance of considering both the quantity of particles and sources (chemical composition), as health metrics for indoor air quality.