Infiltration of PM2.5 into Homes in Toronto, Canada: Can Commonly Available Housing Characteristics Be Used to Improve Exposure Estimates?

Abstract

ISEE-0803 Background and Objective: Epidemiological studies of outdoor air pollution continue to be impacted by errors in estimating personal exposure. Differences in the infiltration of outdoor pollution between homes and over time contribute to exposure errors, but very few epidemiologic studies have considered infiltration because it is not feasible to measure in large numbers of homes and published literature on modeling is still scarce. This study sought to estimate infiltration efficiencies of PM2.5 in detached residential homes in Toronto and identify housing characteristics that could be used to predict infiltration efficiencies. Methods: Fine particulate matter was measured continuously indoors and outdoors for 5-days at 60 detached homes in Toronto, Canada, July through November 2006 and July 2007 using a Dust-Trak. After censoring indoor sources, an average infiltration rate for each home was estimated using a recursive mass balance model with PM2.5 hourly averages. Participating households completed questionnaires on home characteristics and house assessment values were obtained from the Municipal Property Assessment Corporation of Ontario. These variables were offered into linear regression models as predictors of infiltration efficiency. Results: After removal of incomplete and invalid data, 30 homes (50%) remained for inclusion in analyses. Average infiltration rate was 64% (standard dev = 22%); it was higher in the non-heating season (67% ± 23%, n = 21) than in the heating season (56% ± 15%, n = 9), though the difference was not significant. Predictors of higher infiltration were older homes (R2 = 16%) and higher air exchange rate (R2 = 17%) (P < 0.05). In the non-heating season, central air conditioning use also predicted lower infiltration (R2 = 10%, P < 0.05). Other housing characteristics, including house assessment value, were not significantly associated with infiltration rates. Conclusion: Although it remains challenging to predict infiltration rates for individual homes, some easily attainable housing characteristics may allow for the prediction of infiltration in future epidemiological studies of air pollution.