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Chemical Characteristics of PM2.5 during a 2016 Winter Haze Episode in Shijiazhuang, China
Fei Chen1,2, Xiaohua Zhang1, Xinsheng Zhu1, Hui Zhang1, Jixi Gao1,2, Philip K. Hopke3
1 Nanjing Institute of Environmental Sciences, Ministry of Environmental Protection, Nanjing 210042, China
2 Collaborative Innovation Center of Atmospheric Environment and Equipment Technology (CICAEET), Nanjing University of Information Science & Technology, Jiangsu 210044, China
3 Center for Air Resource Engineering and Science, Clarkson University, Potsdam, New York 13699, USA
- Measurements of PM2.5 concentration and composition on hazy and clear days.
- Very high hourly concentrations up to 775 µg m–3 were observed.
- Haze occurs on days of low wind speed and transport from major urban centers.
- Emissions of oxidized species like sulfate and organic carbon from coal combustion.
- Further controls on fuel quality and combustions systems are needed.
To better understand the chemical characteristics and the potential source regions of PM2.5 measured from 18 January until 22 January 2016 in Shijiazhuang, China, PM2.5 was measured continuously and integrated daily sampling using mid-volume samplers was conducted at the three sites. The mean concentration of PM2.5 at the three sites reached 113, 131 and 119 µg m–3 during the sampling period, the higher concentrations occurred at early morning and noon, similar variation trends were found in the three sites. The concentrations of OC were higher than EC at three sampling sites and the OC/EC ratios ranged from 9.09 to 12.4 with a daily mean value of 10.8 during a haze pollution episode (HPE), which suggested that carbonaceous compositions might be from same source. The total concentration of water soluble inorganic ions (WSII) at the sites ranged from 72.2 to 100.0 µg m–3 with a mean of 84.3 µg m–3. The dominant species were NO3–, SO42–, NH4+, Cl–, accounting for 88.4% of the mean PM2.5 WSII mass. The most abundant measured element was Na with average mass concentrations of 41.5, 37.0, and 38.1 µg m–3 during the HPE. Relative humidity during HPE was higher than during clean days with average values of 70.1% and 60.2%, suggesting that high relative humidity and low wind speed favored formation of secondary inorganic ions and accelerated hygroscopic growth. The Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) and a potential source contribution function (PSCF) analysis were used to assess the data. Back-trajectories for the three sites identified similar transport pathways. PSCF analysis showed a significant regional impact on PM2.5 at Shijiazhuang during the polluted period. The potential source areas for PM2.5 in Shijiazhuang were the Beijing-Tianjin region and Shandong Province. The results of the present study show the need for the development of PM2.5 control measurements on a regional scale.
PM2.5; Chemical composition; Meteorological factors; Backward trajectory; Potential source contribution function (PSCF).