Seasonal source shifts and toxicity implications of PM_2.5-bound polycyclic aromatic hydrocarbons in central China: The critical role of underrated local emissions

Polycyclic aromatic hydrocarbons (PAHs), as key toxic and carcinogenic components of PM_2.5, require precise source apportionment and health risk assessment for effective control. This study conducted an atmospheric field campaign from August 2021 to January 2022 in Changsha, a representative city within central China's urban agglomeration, to investigate the characteristics and sources of PAHs. Results showed that the average concentration of PAHs was 7.4 ± 5.4 ng m⁻³, with a pronounced seasonal variation: cold-season concentrations were 5.8 times higher than those in the warm season. A refined source apportionment utilizing organic tracers resolved seven primary sources. Diesel vehicles and non-road machinery were the dominant contributors (30.0%). Notably, the combined contribution from local sources (32.2%), often overlooked in previous studies, including cooking (13.2%), shipping (10.4%), and solvent/petroleum evaporation (8.6%), redefining the emission source structure of PAHs in this inland urban region. Toxicity risk assessment, based on the benzo[a]pyrene equivalent concentration (TEQ_BaP), revealed that 49.4% of daily values during the cold season exceeded the WHO air quality guideline of 1 ng m⁻³. Coal combustion emerged as the most significant contributor to carcinogenic potency, accounting for 36.7% of the total TEQ_BaP. An integrated analysis of meteorological data and potential source regions indicated that stagnant weather conditions, coupled with emissions from local biomass burning and residential coal combustion, were key drivers of high-PAH episodes. Our findings highlight prioritize coordinated management of non-road diesel machinery, cooking emissions, and local residential coal and biomass burning to effectively reduce PAH concentrations and associated public health risks.