[Effect of Liquid Water Content of Particles and Acidity of Particulate Matter on the Formation of Secondary Inorganic Components in Xinjiang Petrochemical Industrial Area]

Secondary species are dominant components of PM_2.5 in Dushanzi, Xinjiang. It is crucial to investigate the conversion process of secondary components in the atmosphere for regional air pollution control. The water-soluble components were analyzed for samples collected from Dushanzi District of Xinjiang from September 2015 to July 2016. The results showed that the total water-soluble ions (TWSIs) showed a seasonal variation consistent with PM_2.5, and the seasonal variation of the ions was in the order-winter (67.86 μg·m^-3) > autumn (13.77 μg·m^-3) > spring (10.09 μg·m^-3) > summer (4.85 μg·m^-3); secondary ions (NH₄⁺, SO₄^2-, and NO₃^-)-accounting for 98% of TWSIs in winter. The results of the aerosol thermodynamic model (E-AIM) that explores the particle liquid water and acidity in Dushanzi District showed that the particles in Dushanzi are acidic with an annual in-situ pH of 0.81, and the pH value of the winter samples was the highest (2.93). The seasonal variation of particles in water was of the order: winter (331.32 μg·m^-3) > autumn (5.91 μg·m^-3) > spring (5.46 μg·m^-3) > summer (1.62 μg·m^-3). The annual average nitrogen oxidation rate and sulfur oxidation rate were 0.13 and 0.47, respectively, indicating a secondary conversion of regional pollutants. Further analysis showed that the concentration of sulfate in the particle phase was significantly affected by liquid water content of particles and in-situ pH. The formation of nitrate was mainly caused by heterogeneous reactions under high water content of particle.

[Distribution Characteristics of Water-soluble Ions in Size-segregated Particulate Matters in Taiyuan]

The distributions of size-segregated particles (PM₁₀) and water-soluble ions (WSIs) in Taiyuan were studied from July 2014 to April 2015 by TE-235 aerosol sampling and ion chromatography analyzing. As the results shown, the daily PM₁₀ level was 173.7 μg·m^-3, which exceeded the Grade Ⅱ limitation value in the Ambient Air Quality Standard (150 μg·m^-3, GB 3095-2012). PM₁₀ levels varied seasonally, and its were 199.1 and 194.2 μg·m^-3 in winter and spring, respectively, which were much higher than those in summer. The PM₁₀ size-segregated was bimodal distribution for the range of 0-0.95 and 3.0-7.2 μm. The concentration of WSIs was the highest in winter, followed by summer and spring. SO₄^2-, NO₃^- and NH₄⁺ were the main water soluble ions and accounted for 66% to 80% of the total WSIs. SO₄^2-, K⁺, NH₄⁺ and Cl^- showed a unimodal distribution at <0.95 μm in all samples, while Ca²⁺ and Mg²⁺ showed a bimodal distribution at <0.95 μm and 3.0-7.2 μm. NO₃^- showed a unimodal size distribution at <0.95 μm in winter and spring, compared with a bimodal distribution at <0.95 μm and 3.0-7.2 μm in summer. By the correlation analysis, PM₁₀ and WSIs decreased with the increase of wind speed in summer and winter other than in spring for the road-dust re-suspension by strong wind. Based on the ratio analysis of NO₃^-/SO₄^2- and Mg²⁺/Ca²⁺, coal combustion was the main source of NO₃^- and SO₄^2-, while Mg²⁺ and Ca²⁺ were mainly from the dust and coal combustion.