Unexpected Increase in PM2.5-Bound Polycyclic Aromatic Hydrocarbons Despite Improved Air Quality: Long-Term Measurements and Source Apportionment in the Pearl River Delta

Abstract

Abstract Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants that pose significant risks to human health. Long‐term observations in PM 2.5 ‐bound PAHs are essential for understanding their source variations and assessing the impacts of emission control strategies. In this study, a total of 22 PAHs were measured at a rural site in the Pearl River Delta over a 12‐year period. Two distinct phases of variation were identified: During 2007–2013 (Phase I), PAH concentrations approximately doubled from 10.72 ± 4.77 ng m −3 to 23.56 ± 12.13 ng m −3 . In contrast, PAH concentrations decreased by 41% to 13.61 ± 7.17 ng m −3 during 2013–2018 (Phase II). Unexpectedly, an apparent increase in PAH mass fractions was identified (3% yr −1 ), which implied that PAH‐associated health risks did not decline despite improved air quality over the past decades. Correlation analysis and source apportionment revealed that PAHs originated primarily from coal combustion, accounting for 55% of the total contribution. In comparison, biomass burning and transportation accounted for 25% and 20%, respectively. Notably, the contributions of coal combustion significantly increased from 34% to 73%, while those of traffic emission and biomass burning decreased from 39% to 13% and from 27% to 14%, respectively. In addition, the persistently high PAH levels were primarily linked to coal combustion, resulting in PAH‐related health risks that remained approximately two orders of magnitude above the acceptable threshold. Our results highlight that future mitigation strategies should shift from a concentration‐based approach toward a health risk‐oriented framework that prioritizes the reduction of highly toxic components and their sources.