Analysis of organic and elemental carbon in heating and non-heating periods in four locations of Beijing

Effect of wet flue gas desulfurization (WFGD) on fine particle (PM2.5) emission from coal-fired boilers

In this study, the characteristics of fine particles before and after wet flue gas desulfurization (WFGD) in three coal-fired heating boilers in northern China were investigated by using a dilution-based emission sampling experimental system. The influences of the WFGD process on the mass and number concentrations as well as the chemical composition of fine particles were analyzed. The removal efficiency of desulfurization processes on particulate matter mass was 30.06%-56.25% for the three study units. The WFGD had a great influence on the size distributions of particle mass concentration and number concentration. A significant increase in the number and mass concentration of particles in the size range of 0.094-0.946 μm was observed. The water-soluble ion content accounted for a very large proportion of PM_2.5 mass, and its proportion in PM_2.5 increased from 28.39%-41.08% to 48.96%-61.21% after the WFGD process for the three units. The desulfurizing process also drastically increased the proportion of cation component (Ca²⁺ for unit A, Mg²⁺ for unit B, and Na⁺ for unit C) and the proportion of SO₄^2- in PM_2.5, and it increased the CE/AE values of PM_2.5 from 0.82-0.98 to 0.93-1.27 for the three study units.

Temporal-spatial characteristics and source apportionment of PM2.5 as well as its associated chemical species in the Beijing-Tianjin-Hebei region of China

PM_2.5 and its major chemical compositions were sampled and analyzed in January, April, July and October of 2014 at Beijing (BJ), Tianjin (TJ), Langfang (LF) and Baoding (BD) in order to probe the temporal and spatial characteristics as well as source apportionment of PM_2.5 in the Beijing-Tianjin-Hebei (BTH) region. The results showed that PM_2.5 pollution was severe in the BTH region. The average annual concentrations of PM_2.5 at four sampling sites were in the range of 126-180 μg/m³, with more than 95% of sampling days exceeding 35 μg/m³, the limit ceiling of average annual concentration of PM_2.5 regulated in the Chinese National Ambient Air Quality Standards (GB3095-2012). Additionally, concentrations of PM_2.5 and its major chemical species were seasonally dependent and demonstrated spatially similar variation characteristics in the BTH region. Concentration of toxic heavy metals, such as As, Cd, Cr, Cu, Mn, Ni, Pb, Sb, Se, and Zn, were higher in winter and autumn. Secondary inorganic ions (SO₄^2-, NO₃^-, and NH₄⁺) were the three-major water-soluble inorganic ions (WSIIs) of PM_2.5 and their mass ratios to PM_2.5 were higher in summer and autumn. The organic carbon (OC) and elemental carbon (EC) concentrations were lower in spring and summer than in autumn and winter. Five factors were selected in Positive Matrix Factorization (PMF) model analysis, and the results showed that PM_2.5 pollution was dominated by vehicle emissions in Beijing, combustion emissions including coal burning and biomass combustion in Langfang and Baoding, and soil and construction dust emissions in Tianjin, respectively. The air mass that were derived from the south and southeast local areas around BTH regions reflected the features of short-distant and small-scale air transport. Shandong, Henan, and Hebei were identified the major potential sources-areas of secondary aerosol emissions to PM_2.5.