Abstract
Much attention has been given to the distributions, sources, and health risks of atmospheric polycyclic aromatic hydrocarbons (PAHs) in cities. In this study, a total of 62 suspended particle samples were collected from April 2013 till March 2014 in the city of Lhasa. Positive matrix factorization (PMF) was applied to investigate the source apportionment of 15 priority PAHs, the lifetime carcinogenic risk (LCR) levels of which were assessed. The average annual particle phase PAH concentration was 43.9 ± 60.4 ng m–3. Evident seasonal variations of PAHs were observed, with the highest concentration observed in winter, followed by autumn, spring, and summer. Four- and five-ring PAHs accounted for the predominant proportion (63.3%–84.4%) throughout the year. Correspondingly, gas phase PAHs showed the opposite variations, with the highest and lowest concentrations observed in summer and winter, respectively; also, three-ring PAHs, especially Ace, Acel, and Flu, were the largest contributors. Compositions of particle phase PAHs varied seasonally, with four-ring PAHs contributing more in winter than in summer and five-ring PAHs exhibiting the opposite trend, thereby reflecting the variety of emission sources. PMF analysis showed that biomass combustion (48.4%) and vehicle emissions (27.9%) were the two main sources, followed by coal combustion and the air–surface exchange. These results were consistent with the diagnostic molecular ratios. The benzo(a)pyrene equivalent (BaPeq) concentration of particle phase PAHs ranged from 1.48 to 24.5 ng m–3, which exceeds were higher than the new limit in China (1 ng m–3). The average BaPeq of gas phase PAHs was 6.43 ± 4.15 ng m–3, which was similar to that of particle phase PAHs. The LCR of the total PAHs (9.08 × 10–6) was one time higher than that of the particle phase; however, it was slightly lower than the acceptable level, thereby indicating that atmospheric PAHs in Lhasa pose little or no carcinogenic risk to the local population.
Highlights
Polycyclic aromatic hydrocarbons (PAHs) compose a large group of organic compounds that consist of fused aromatic rings
The annual average polycyclic aromatic hydrocarbons (PAHs) concentration was considerably lower than those reported in numerous areas of northern China such as Shanxi, Shandong, and Beijing (Zhang et al, 2016) and South Asia such as Kathmandu (Chen et al, 2015) and Delhi (Sarkar and Khillare, 2013), it was higher than those observed at background sites in the Tibetan Plateau (TP)
The PAH concentration had increased since the two studies conducted in Lhasa in 2006 and 2007 (Table 2), implying that emissions might have increased as a result of urbanization (Gong et al, 2011; Liu et al, 2013)
Summary
Polycyclic aromatic hydrocarbons (PAHs) compose a large group of organic compounds that consist of fused aromatic rings. They are emitted mainly from the incomplete combustion or pyrolysis of organic materials such as coal, oil, gas, waste, and biomass (Ravindra et al, 2008; Zhang and Tao, 2009). Anthropogenic emissions within the TP are not of major concern compared with those in densely populated and industrialized parts of South and East Asia. Numerous recent studies have reported atmospheric pollutants in this remote region (Cong et al, 2015a; Lüthi et al, 2015; Li et al, 2016); such studies have primarily been concerned with the role of the long-range transportation of pollutants emitted from South Asia. Local anthropogenic activity in the TP contributes significantly to the atmospheric environment (Gong et al, 2011; Li et al, 2012; Chen et al, 2015a; Li et al, 2016a)
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