Sources of indoor PM2.5 gross α and β activities measured in 340 homes

Particle radioactivity (PR) exposure has been linked to adverse health effects. PR refers to the presence of alpha- and beta-emitting radioisotopes attached to fine particulate matter (PM2.5). This study investigated sources contributing to indoor PM2.5 gross alpha- and beta-radioactivity levels. We measured activity from long-lived radon progeny radionuclides from archived PM2.5 samples collected in 340 homes in Massachusetts during the period 2006-2010. We analyzed the data using linear mixed effects models and positive matrix factorization (PMF) analysis. Indoor PM2.5 gross alpha-activity levels were correlated with sulfur (S), iron (Fe), bromine (Br), vanadium (V), sodium (Na), lead (Pb), potassium (K), calcium (Ca), silicon (Si), zinc (Zn), arsenic (As), titanium (Ti), radon (Rn-222) and black carbon (BC) concentrations (p <0.05). Indoor PM2.5 beta-activity was correlated with S, As, antimony (Sb), Pb, Br and BC. We identified four indoor PM2.5 sources: outdoor air pollution (62%), salt aerosol source (14%), fireworks and environmental tobacco smoke (7%) and indoor mixed dust (17%). Outdoor air pollution was the most significant contributor to indoor PM2.5 alpha- and beta-activity levels. The contributions of this source were during the summer months and when windows were open. Indoor mixed dust was also found to contribute to PM2.5 alpha-activity. PM2.5 alpha-activity was further associated with radon during winter months, showing radon's important role as an indoor source of ionizing radiation.