Chemical Characteristics of PM2.5 during a 2016 Winter Haze Episode in Shijiazhuang, China

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 mu g 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 mu g m(-3) with a mean of 84.3 mu g 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 mu g 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.