Variations of source-specific risks for inhalable particles-bound PAHs during long-term air pollution controls in a Chinese megacity: Impact of gas/particle partitioning

Gas/particle (G/P) partitioning is a determining factor that drives the behavior of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. To comprehend the variations and impacts of PAHs G/P partitioning on inhalation risks from different sources, atmospheric PAHs in Chengdu were studied from January 2009 to January 2021. Chengdu ' s air quality demonstrated improvement, with a noticeable decline in PM 10 (from 238 to 103 mu g m -3 ), PM 10 -bound PAHs mass concentrations (from 0.08 to 0.01 mu g m - 3 ), as well as PAHs inhalation noncancer (from 63.5 to 7.1) and cancer risks (from 6.2 x 10 -5 to 7.7 x 10 -6 ). Decreasing trends were also observed in the concentrations of organic carbon (OC) and the values of absorptive G/P partitioning coefficient ( K p, OM ) from 2009 to 2020, indicating a slight decrease in the PM absorptive capacity. A positive matrix factorization (PMF) model utilized three distinct datasets: PMF pp (particle -phase PAHs only), PMF tot (total PAHs concentrations), and PMF pp/gas (particle -phase in parallel with gas -phase PAHs). PMF pp and PMF pp/gas provide reasonable source apportionment and source -specific risk results. However, daily variations in source contributions of PMF tot were found to be unreasonable. PMF pp/gas and PMF tot could identify a source of low molecular weight PAHs (LPAHs) related to temperature, and a significantly positive correlation between LPAHs and temperature was discovered. Gas/particle partitioning of PAHs showed a notable impact on source -specific risks associated with coal and biomass combustion (CC &BC). The findings contribute to our understanding of the variation in PAHs G/P partitioning and the PM absorptive capacity resulting from effective air pollution control in China. Additionally, they offer prerequisite information for incorporating semi -volatile organic compounds in source apportionment and source -specific risk assessment.