Behavior Variability of Source-Specific Toxic Components in the Respiratory Tract: Coeffects of Size Distribution, Phase Partitioning, and Particulate Matter Composition

Particulate matter (PM) exhibits diverse characteristics (such as chemical composition, size) that influence its interactions with the human body and associated health risks. Limited knowledge of toxic components' behaviors in the respiratory system hinders understanding of source-specific risks. This study developed a source apportionment and respiratory mass transfer coupling method to model toxic components' behaviors and assess health risk. Analysis and modeling of 93 toxic components in nine-stage PM and gas samples from a Chinese megacity, revealed that potential toxic elements from different sources primarily deposited in the pulmonary region (PR) or dissolved in the upper respiratory (UR) and tracheobronchial region (TR) tracts. High-volatility and -solubility organics dissolved readily in UR and TR, while low-volatility and -solubility organics accumulated in PR. Industrial emissions dominated cancer risks across regions (incremental lifetime cancer risk: 1.04 × 10^-5 in UR), while coal combustion, industrial emissions, and resuspended dust primarily contributed to noncancer risks. Arsenic from industrial emissions posed significant PR risks due to its accumulation in finer sizes, and traffic-emitted organics showed high pulmonary fractions due to strong absorption by carbonaceous components. This study provides novel insights into how PM characteristics influence toxic components' behaviors and source-specific health risks.