Chemical Characteristics and Potential Sources of PM2.5 in Shahe City during Severe Haze Pollution Episodes in the Winter

ABSTRACT

In recent years, North China has suffered from severe air pollution. Hence, this study performed a comprehensive field experiment during Dec. 2017 in Shahe (114.5°N, 36.85°E), a typical industrial city in this region that is characterized by intensive NO_x emission from the local glassmaking industry. During the study period, the mass concentration of the PM_2.5 (fine particulate matter) averaged 121.6 ± 91.8 µg m^–3, whereas the mass concentrations of the nitrate and sulfate in the PM_2.5 averaged 21.4 ± 16.3 and 15.9 ± 20.9 µg m^–3, respectively. The high sulfate mass concentration primarily resulted from the oxidation of SO₂, which was mainly due to gas-phase and heterogeneous reactions during low relative humidity (RH; < 40%) and enhanced aqueous reactions during high RH (> 40%). In addition, because the nitrogen oxidation ratio (NOR) increased as the RH decreased during the day, the nitrate was largely generated through photochemical reactions. The mass concentrations of the optical organic carbon (OC), elemental carbon (EC), and water-soluble organic compounds (WSOCs) equaled 50.4 ± 31.1, 5.8 ± 4.4, and 12.8 ± 10.1 µgC m^–3, respectively, and applying the EC tracer method revealed that primary emissions contributed approximately 72% of the total OC. Furthermore, intense industrial activities were detected in a nearby area to the northeast, which potential source contribution function (PSCF) analysis identified as the main potential source area for PM_2.5 during haze.