Physico-chemical characterization of PM2.5 in the microenvironment of Shanghai subway

• Published in: Atmospheric research 2015-02, Vol.153, p.543-552
• Main Authors: Lu, Senlin, Liu, Dingyu, Zhang, Wenchao, Liu, Pinwei, Fei, Yi, Gu, Yan, Wu, Minghong, Yu, Shang, Yonemochi, Shinich, Wang, Xiaoju, Wang, Qingyue
• Format: Article
• Language: English
• Subjects: Aluminum; Iron; Minerals; Physicochemcial characterization; PM2.5; Shanghai subway system; Speciation; Suburban areas; Subway stations; Subways; Zinc
• ISSN: 0169-8095; 1873-2895
• DOI: 10.1016/j.atmosres.2014.10.006

The Shanghai subway metro system has brought great convenience to the city's travelling public, although passengers are exposed to airborne particles in this built micro-environment. However, investigations on the physicochemical characterization of PM2.5 air pollution in the Shanghai subway system are to date very limited. Three subway stations along the No. 7 line were selected as subway PM2.5 monitoring sites: Pan'guang, Shanghai University (SHU), and Jing'an, which are located in an outer suburban area, a suburban area and the urban area, respectively, airborne PM2.5 on the subway station platforms and in the ambient atmosphere above-ground was synchronously collected from 19th March to 4th, May, 2012. Cutting-edge techniques, including scanning electronic microscopy coupled with energy dispersive X-ray (SEM/EDX), inductively coupled plasma mass spectrometry (ICP-MS) and X-ray absorption near-edge structure (XANES) were employed to investigate microscopic characterization, chemical elements and speciation of the main heavy metals in subway PM2.5. Our results demonstrated that mass levels of PM2.5 in the subway stations were higher than that in ambient air. Mass levels of PM2.5 in the subway stations and in ambient air ranged from 49.17±19.7μg/m3 to 66.15±25.20μg/m3, and 24.52±3.3μg/m3 to 65.60±5.6μg/m3, respectively. The microscopic characterization of PM2.5 in ambient air and in subway stations showed marked differences. The PM2.5 in the subway stations was mainly composed of iron-containing particles and mineral particles, while the PM2.5 in ambient air largely consisted of mineral particles and soot aggregates. Fe was the most abundant element in subway PM2.5, followed by: major elements (mass level>100ng/m3) including Na, Mg, Al, K, Ca, Zn, Mn, Ba; sub-major elements (10ng/m3