Spatio-temporal distribution and influencing factors of atmospheric polycyclic aromatic hydrocarbons in the Yangtze River Delta

In this study, we collected samples of atmospheric polycyclic aromatic hydrocarbons (PAHs) in the Yangtze River Delta (YRD), one of the most developed regions in China, during four seasons, from June 2017 to May 2018. We identified the spatiotemporal distribution of PAHs in YRD, and analyzed the factors (source contribution, meteorological conditions, and backward trajectory) influencing these concentrations. First, our results showed that the average PAH concentration was 41.46 ± 15.57 ng/m3 in YRD, and was highest in Jiangsu (44.47 ± 11.37 ng/m3). The concentration of PAHs has decreased since 2001. The relatively balanced development of urban and rural areas in the YRD has resulted in a relatively low ratio (∼1.12) of PAHs between urban and rural areas. The PAH level in YRD was highest in winter (52.21 ± 14.70 ng/m3) and lowest in summer (31.23 ± 12.88 ng/m3). Second, principal component and multivariate linear regression analyses (PCA-MLR) were used to identify three main PAH sources: vehicle emissions (52.83%), coke ovens and volatilization (23.67%), and coal and biomass combustion (23.51%). The seasonal variations in the PAH source contribution were mainly attributed to seasonal differences in the amounts of coal and biomass burned, the prevailing wind direction, and traffic control in winter. Third, we found that the PAH concentrations were significantly negatively correlated with the temperature, precipitation, and relative humidity throughout the year. Finally, backward trajectory analysis indicated that the PAHs in YRD were significantly affected by air masses from northern China, particularly during winter. The results of this study suggest that enforcing stricter controls on coal and biomass combustion in northern China, improving the fuel quality of vehicles, increasing the proportion of gas/electric vehicles, and strengthening the joint control of air pollution could further reduce the PAH concentrations in China. The analysis conducted in this study will help develop pollution control strategies to reduce lung cancer risk for the whole YRD region.