Fine particulate matter infiltration at skilled nursing facilities during wildfire season in the Western United States

Abstract

Background and Aim: Wildfire air pollution is a growing public health concern as wildfires increase in size, intensity, and duration in the United States (US). Residents of skilled nursing facilities (SNFs) are vulnerable to wildfire smoke due to common pre-existing health conditions and advanced age of these populations. We assessed the impact of wildfire smoke on SNFs by estimating ambient fine particulate matter (PM₂.₅) infiltration into SNFs during wildfire season. Methods: We measured continuous outdoor and indoor PM₂.₅ concentrations from July-October 2021 at six SNFs in the US states of Idaho and Montana using PurpleAir monitors. We calculated infiltration efficiency (range 0-1; higher values indicate more ambient PM₂.₅ infiltration to the indoor environment) at each facility using paired outdoor/indoor PM₂.₅ samples in a validated recursive modeling approach. Analyses were conducted separately for each facility, by time of day (8am-5pm work hours versus after hours), and by days impacted by wildfire smoke. Results: Median outdoor PM₂.₅ at the SNFs ranged from 7.9 µg/m³ (25th percentile=4.4, 75th percentile=21.6) to 16.0 µg/m³ (25th percentile=7.4, 75th percentile=30.6). Median indoor PM₂.₅ at the SNFs ranged from 2.1 µg/m³ (25th percentile=1.7, 75th percentile=3.9) to 8.4 µg/m³ (25th percentile=2.0, 75th percentile=15.8). Infiltration efficiency at the facilities ranged from 0.13 (95% Confidence Interval: 0.10, 0.18) to 0.74 (95% Confidence Interval: 0.64, 0.85). Infiltration efficiency was similar during work hours versus after hours, but was higher during wildfire-impacted days than non-wildfire-impacted days for all but one facility. Conclusions: The high variability of indoor PM₂.₅ and infiltration efficiency across the facilities suggests that indoor exposures to wildfire smoke may be a modifiable risk factor for SNF residents. Future work will assess building characteristics and behavioral factors among residents and staff that may be related to wildfire smoke infiltration. Keywords: smoke, wildfires, indoor air pollution, vulnerable populations, infiltration efficiency, PM₂.₅