[Atmospheric Pollution Characteristics and Inhalation Exposure Risk of Nitrated Polycyclic Aromatic Hydrocarbons in PM at the Ningdong Energy and Chemical Industry Base, Northwest China].

Atmospheric PM samples were collected by using the active sampling method to investigate the pollution characteristics of nitrated polycyclic aromatic hydrocarbons (NPAHs) at the Ningdong Energy and Chemical Industry Base, Northwest China. Furthermore, the primary sources and the contributions of secondary formation sources as well as the inhalation exposure risks were identified. The main results were as follows. The concentration levels of ∑NPAHs in PM ranged from 2.06 ng·m to 37.14 ng·m at the Ningdong Energy and Chemical Industry Base. The average concentrations of ∑NPAHs were (25.57±5.76) ng·m in winter and (6.22±1.74) ng·m in summer for the Baofeng sampling site associated with the energy industry. The average concentrations of ∑NPAHs were (7.13±1.44) ng·m in winter and (2.58±0.39) ng·m in summer for the Yinglite sampling site associated with chemical and electricity industries. The levels of ∑NPAHs in PM were higher in winter than those in summer because of the increased heating in winter. Atmospheric pollution levels of NPAHs at the Baofeng sampling site were generally higher than those at the Yinglite sampling because of the higher primary NPAHs emissions from coal mining and coke production in Baofeng compared with those from the chemical industry in Yinglite. The calculated nocturnal/diurnal ratios revealed that the concentrations of ∑NPAHs in PM during the summer season were higher in the daytime than those in the nighttime, but the opposite trend occurred in winter, thus indicating that secondary formation processes made more contributions to NPAHs during summer in the daytime. The congener profiles of NPAHs were mainly composed of primary emission markers such as 2-nitrofluorene (2N-FLO) and 6-nitrochrysene (6N-CHR), which were the predominant ones in winter and summer for both the Baofeng and Yinglite sampling sites. Total proportions of 2N-FLO and 6N-CHR were 46% in winter and 73% in summer for Baofeng and 59% in winter and 55% in summer for Yinglite, respectively. Meanwhile, 3N-PHE, which is a marker compound of secondary formation processes, accounted for a higher percentage in summer especially at Yinglite. This finding revealed that the chemical production at Yinglite was associated with higher precursor emissions than that of Baofeng, and thus, more NPAHs were derived from secondary formation processes. Moreover, ∑NPAHs/∑PAHs ratios were calculated to identify the potential sources of NPAHs across the city. The results indicated that higher environmental temperatures in summer promoted the degradation of PAHs and secondary formation of NPAHs, and thus, secondary formation contributed more to NPAHs in summer than in winter. Furthermore, lung cancer risks induced by inhalation exposures to ∑NPAHs were assessed based on the BaP equivalent toxicity factor. The results showed that the lung cancer risk values of ∑NPAHs were (3.06×10±1.36×10) in winter and (1.79×10±0.80×10) in summer for the Baofeng sampling site, while the risk values were (2.85×10±1.20×10) in winter and (1.86×10±0.83×10) in summer for the Yinglite sampling site. Notably, the lung cancer risk values in our study for both sampling sites were higher than the standard limit value (1.00×10) of the California Environmental Protection Agency, which indicates that the local population at the Ningdong Energy and Chemical Industry Base has been subjected to potentially elevated lung cancer risks due to inhalation exposures to PM-bound NPAHs.