Pollution characteristics and health risk of polycyclic aromatic hydrocarbons in PM_2.5 in the Pearl River Delta, China, 2016-2022

Objective To investigate population health risk of exposure to polycyclic aromatic hydrocarbons (PAHs), as well as the pollution characteristics and sources of atmospheric PM_2.5 and 16 PAHs in the Pearl River Delta.

Methods From 2016 to 2022, 10 monitoring points were set up in 10 districts of Guangzhou, Shenzhen, Foshan, and Zhuhai in the Pearl River Delta region of Guangdong Province, China. Ambient air samples were collected from the 10th day to the 16th day of each month to determine the concentrations of PM_2.5 and 16 PAHs, and the pollution sources of PAHs were analyzed. The BaP toxicity equivalent method was used to evaluate the population health risk of respiratory exposure to PAHs.

Results The mean annual concentrations of PM_2.5 (x±s) in the Pearl River Delta from 2016 to 2022 were 57.45±29.66, 51.26±35.69, 43.86±33.17, 40.53±24.70, 29.26±34.27, 31.57±24.91, and 30.17±21.06 μg/m³, respectively, which showed a decreasing trend (Z=-29.83, P < 0.01). The mean concentrations of PAHs (x±s) were 6.23±6.29, 5.17±6.95, 4.00±4.46, 3.34±3.93, 2.52±2.92, 3.05±4.30, and 2.65±2.60 ng/m³, respectively, and although the concentrations of PAHs were reduced by nearly 60%, there was no statistical significance in the decreasing trend. All 16 PAHs except naphthalene showed a decreasing trend (P < 0.05). The median CR (P₂₅, P₇₅) of the carcinogenic effect of PAHs in PM_2.5 from 2018 to 2022 was 5.35×10^-7 (2.54×10^-7, 1.21×10^-6); it was greater than 1×10^-6 from the 69th percentile and was 9.19×10^-6 at the 99th percentile, all lower than 1×10^-4.

Conclusion There is a tendency of continuous improvement in atmospheric PM_2.5 pollution in the four cities of the Pearl River Delta, and among the four cities, Shenzhen and Zhuhai have a better air quality than Foshan and Guangzhou. The content of PM_2.5 is significantly positively correlated with that of PAHs, with a basically consistent changing trend month by month. Local emissions are the main sources of PAHs pollution, including fossil fuel combustion, vehicle exhaust emissions, petroleum volatilization, and organic matter combustion. There are certain differences in the composition and sources of PAHs pollution among cities, and high-temperature coal burning has an important impact on the change in the concentration of PAHs. PAHs in atmospheric PM_2.5 have a potential carcinogenic risk and should be taken seriously.