Evaluating the representativeness of atmospheric PM_2.5 data for indoor exposure: insights from concentrations,...

Studies relied on atmospheric PM_2.5 data to estimate health risks and sources, but its representativeness for indoor air remains unclear. This study placed an atmospheric PM_2.5 sampler on the rooftop of a three-story building, and indoor and outdoor (balcony) samples were collected from study houses within a 5 km radius of the atmospheric sampling site during low and high PM_2.5 seasons to evaluate the representativeness of atmospheric PM_2.5 data. The average PM_2.5 concentrations were 15.4 ± 7.1 μg/m³ (indoor), 18.9 ± 7.0 μg/m³ (outdoor), and 13.9 ± 6.1 μg/m³ (atmospheric). Atmospheric PM_2.5 concentrations were significantly associated with indoor and outdoor PM_2.5, but outdoor PM_2.5 concentrations were higher. Source identification revealed that traffic-related emission was a major contributor to PM_2.5 across all sites and seasons, while long-range transport from China was another source during the high PM_2.5 season based on lead isotope ratios. Crustal elements and construction dust, identified through positive matrix factorization, were higher in both indoor and outdoor air than in the atmosphere. Elements from industrial or traffic emissions showed similar concentrations across different sampling sites. The average ratios of indoor to outdoor or atmospheric PM_2.5 concentrations were 0.84 ± 0.27 and 1.18 ± 0.37, respectively. In conclusion, atmospheric PM_2.5 can be used to estimate PM_2.5 exposure and element concentrations from industrial or traffic emissions in indoors; however, it underestimates the contributions of crustal elements and construction dust. Ambient PM_2.5 samples from outdoor or atmospheric environments should be considered when comparing their influence on indoor air across studies.