The impact of a community-wide woodstove changeout intervention on air quality within two schools

Due to temperature inversions and widespread residential woodstove use, Libby, Montana historically experienced elevated levels of ambient woodsmoke PM_2.5 throughout the winter months. In an effort to reduce wintertime PM_2.5, a large community-wide woodstove changeout was conducted between 2005 and 2007, removing nearly 1 200 old polluting stoves from service. To determine the impact of this intervention on indoor air quality, PM_2.5 sampling was conducted in the gymnasiums of an elementary and middle school before, during, and after the woodstove changeout over a four-year period. Throughout the program, results showed that indoor PM_2.5 concentrations at the elementary school were moderately high regardless of year or season (mean±sd, 31.9±14.1 μg/m³), ranging from 11.0 μg/m³ to 79.3 μg/m³. At the middle school, the mean was 12.2±11.2 μg/m³, with no differences by season. Although there was an overall improvement in ambient air quality (and reduction of woodsmoke-PM_2.5) when comparing pre- and post-changeout PM_2.5 concentrations, results suggest that the community-wide woodstove changeout did not have a significant impact on indoor air quality within the gymnasiums over this same time period. These findings are supported by the results of selected chemical markers of woodsmoke measured from indoor PM (including levoglucosan) at both schools, which also demonstrated no significant reductions throughout the four-year sampling program.