Indoor particulate matter in rural, wood stove heated homes

Ambient particulate matter (PM) exposures have adverse impacts on public health, but research evaluating indoor PM concentrations in rural homes in the United States using wood as fuel for heating is limited. Our objectives were to characterize indoor PM mass and particle number concentrations (PNCs), quantify infiltration of outdoor PM into the indoor environment, and investigate potential predictors of concentrations and infiltration in 96 homes in the northwestern US and Alaska using wood stoves as the primary source of heating. During two forty-eight hour sampling periods during the pre-intervention winter of a randomized trial, we assessed PM mass (<2.5μm) and PNCs (particles/cm³) in six size fractions (0.30-0.49, 0.50-0.99, 1.00-2.49, 2.5-5.0, 5.0-10.0, 10.0+μm). Daily mean (sd) PM_2.5 concentrations were 28.8 (28.5)μg/m³ during the first sampling period and 29.1 (30.1)μg/m³ during the second period. In repeated measures analyses, household income was inversely associated with PM_2.5 and smaller size fraction PNCs, in particular. Time of day was a significant predictor of indoor and outdoor PM_2.5 concentrations, and infiltration efficiency was relatively low (F_inf (sd)=0.27 (0.20)). Our findings demonstrate relatively high mean PM concentrations in these wood burning homes and suggest potential targets for interventions for improving indoor air quality and health in rural settings.