Inequities in Indoor Exposure to Wildfire-Related PM2.5 Across the Contiguous United States

Exposure to wildfire smoke has been recognized as a major public health concern, but existing studies have focused on outdoor air, despite the fact that most people spend the majority of their time indoors, especially during wildfires. Here, we estimated indoor wildfire-related fine particulate matter (PM2.5) concentrations across 72,537 census tracts in the contiguous United States for the year 2020, examining inequalities among various demographic groups regarding race–ethnicity, socioeconomic status, and other factors. Our results indicate that, in contrast to outdoor air, there are significant inequalities in indoor exposure. Once wildfire-related PM2.5 infiltrates indoor environments, the population-weighted average exposure in disadvantaged communities (DACs) is significantly greater than that in non-DACs. Furthermore, our findings suggest that patterns of inequality at the national level differ from those at the state level. The racial–ethnic groups most affected vary by state, highlighting the need for localized interventions to address wildfire-related PM2.5 exposure.