Real-time indoor PM monitoring in an urban cohort: Implications for exposure disparities and source control.

Fine particulate matter (PM) concentrations are highly variable indoors, with evidence for exposure disparities. Real-time monitoring coupled with novel statistical approaches can better characterize drivers of elevated PM indoors. We collected real-time PM data in 71 homes in an urban community of Greater Boston, Massachusetts using Alphasense OPC-N2 monitors. We estimated indoor PM concentrations of non-ambient origin using mass balance principles, and investigated their associations with indoor source activities at the 0.50 to 0.95 exposure quantiles using mixed effects quantile regressions, overall and by homeownership. On average, the majority of indoor PM concentrations were of non-ambient origin (≥77%), with a higher proportion at increasing quantiles of the exposure distribution. Major source predictors of non-ambient PM concentrations at the upper quantile (0.95) were cooking (1.4-23 μg/m) and smoking (15 μg/m, only among renters), with concentrations also increasing with range hood use (3.6 μg/m) and during the heating season (5.6 μg/m). Across quantiles, renters in multifamily housing experienced a higher proportion of PM concentrations from non-ambient sources than homeowners in single- and multifamily housing. Renters also more frequently reported cooking, smoking, spray air freshener use, and second-hand smoke exposure, and lived in units with higher air exchange rate and building density. Accounting for these factors explained observed PM exposure disparities by homeownership, particularly in the upper exposure quantiles. Our results suggest that renters in multifamily housing may experience higher PM exposures due to a combination of behavioral and building factors that are amenable to intervention.