[Characteristics of Haze Pollution Episodes During Autumn and Winter in 2018 in Shijiazhuang]

The mass concentration and chemical composition of fine particles were continuously observed on-line from October 31 to December 3, 2018 at Hebei Key Laboratory of Haze Pollution Prevention and Control in Shijiazhuang. The characteristics of haze pollution in autumn and winter in Shijiazhuang were analyzed. The results showed that during the observation period, four haze pollution episodes occurred with PM_2.5 as the primary pollutant, and the maximum daily concentration was 154, 228, 379, and 223 μg·m^-3, respectively, reaching a heavy pollution level or above. The main components of PM_2.5were water-soluble inorganic ions (WSⅡ) and carbon-containing aerosols, accounting for (60.7±15.6)% and (21.6±9.7)% of PM_2.5 mass concentration, respectively. Compared with clean days, the mass concentration of WSⅡ and carbon aerosol during haze pollution increased by 4.4 times and 3.1 times, respectively, which was the main cause of haze pollution. NO₃^-, SO₄^2-, and NH₄⁺(SNA) were the main components of WSⅡ, accounting for (91.5±17.3)% of the total WSⅡ concentration, of which NO₃^- took up the highest proportion. The explosive growth of SNA during haze pollution was the main reason for the extremely high PM_2.5concentration. Under non-high humidity conditions, the formation rates of unit mass substrates (NO₃^-, SO₄^2-) were not significantly different, but the transformation of SO₄^2- was significantly promoted after the liquid phase oxidation of SO₂ was triggered under high humidity conditions. The atmosphere in Shijiazhuang is rich in NH₃, and the molar ratio of n(NH₄⁺) to n(NO₃^-+2×SO₄^2-) in PM_2.5 was greater than 1. The presence of a large amount of NH₃ could promote the transformation of NO₃^- and SO₄^2- and aggravate pollution. During the haze pollution period, the accumulation of primary pollutants from coal and motor vehicles was the main reason for the increase in carbon-containing aerosol. Compared with clean days, the formation of SOC was inhibited. Before the beginning of the warm season, the mobile form was the main pollution source of PM_2.5, contributing 30.8% and 39.8% of PM_2.5 mass concentration. With the increase of coal combustion emissions, the contribution of coal-fired sources gradually increased to 25.5%, becoming the primary pollution source.