Chemical composition and morphology of PM_2.5 in a rural valley during Chinese New Year's Eve: Impact of firework/firecracker display

To study the effect of fireworks/firecrackers (FF) display on aerosol particles, the chemical composition and morphology of fine aerosol particles (PM2.5) collected in a rural valley of north China in the Chinese New Year's Eve (CNYE) were analyzed. The results showed that PM2.5 was much lower in the 2022 CNYE with little influence by FF due to the strict no-FF display policy for the 2022 Winter Olympic Games. In contrast, PM2.5 was significantly affected by FF display in the 2023 CNYE with the maximum hourly PM2.5 mass concentrations reaching 1200 mu g m(-3). The value was even much higher than that in near-by cities. Chemical analysis showed that organic matter (24.5 wt% of total PM2.5) was the most abundant in the CNYE, followed by K+ (15.3 wt%), SO42- (12.3 wt%), and Cl (9.9 wt%). The mass concentrations of K+, Mg2+, Cu, Sr, and Ba were as 22.0 to 41.4 times as those before the CNYE. The concentrations of elemental carbon, Cl, SO42-, and Ti were as 3.7 to 12.3 times as those before the CNYE. Further analysis by scanning electron microscope coupled with energy dispersive X-ray spectrometer revealed that carbonaceous particles in the CNYE contained more S, Cl, K and heavy metals compared with that before the CNYE. Most of the non-carbonaceous particles in the CNYE were K-rich, Mg-rich, Al-rich, and Ba-rich, with spherical and near-spherical shapes, which were much different from those before the CNYE with irregular shapes. The different morphologies of non-carbonaceous particles can have much different optical properties, which should be further evaluated. The results above suggested that the PM2.5 mass concentration in rural valleys in the CNYE was extremely high in a short time and more attention should be paid in future policy making to improve air quality.