Real-time indoor PM_2.5 monitoring in an urban cohort: Implications for exposure disparities and source control

Fine particulate matter (PM_2.5) 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_2.5 indoors. We collected real-time PM_2.5 data in 71 homes in an urban community of Greater Boston, Massachusetts using Alphasense OPC-N2 monitors. We estimated indoor PM_2.5 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_2.5 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_2.5 concentrations at the upper quantile (0.95) were cooking (1.4-23 μg/m³) and smoking (15 μg/m³, only among renters), with concentrations also increasing with range hood use (3.6 μg/m³) and during the heating season (5.6 μg/m³). Across quantiles, renters in multifamily housing experienced a higher proportion of PM_2.5 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_2.5 exposure disparities by homeownership, particularly in the upper exposure quantiles. Our results suggest that renters in multifamily housing may experience higher PM_2.5 exposures due to a combination of behavioral and building factors that are amenable to intervention.