Chemical pollution characteristics of PM₁₀and PM_2.5 during heavy air pollution in spring and winter in four functional areas of Beijing and their associated influencing factors

PM₁₀ and PM_2.5 samples were sampled at four sites located in four functional regions of Beijing, including West 3-Ring Road (traffic site), Huayuan North Road (commercial area), Changping countryside (rural area), and Milu Park (suburban area), during four heavy pollution processes in spring and winter, 2015. Principal components analysis (PCA) was used to analyze the sources of PM₁₀and PM_2.5 obtained from the four sampling sites. The pollution characteristic of chemical components, including ten water-soluble ions, organic carbon/element carbon, 16 polycyclic aromatic hydrocarbons (PAHs) and seven heavy metal elements (Zn, Mn, Pb, Ni, Cu, Cr and As), were analyzed. Combined with meteorological conditions and back trajectory, the meteorological influencing factors and the differences of particulate matter chemical compositions of several typical pollution events were discussed. The results showed that the daily-average PM₁₀ and PM_2.5concentrations of West 3-Ring Road on April 9 and 15, Huayuan North Road on March 16-17, Changping rural area on November 12-16, and Milu Park on March 28-29 were greater than 200 and 100 μg/m ³, respectively, which exceeded the Class Ⅱ concentration limits in Ambient Air Quality Standards (GB 3095-2012), and belonged to heavy pollution weathers. The major chemical components in the particulate matter at the four sampling sites were secondary water-soluble ions ${\mathrm{NO}}_3^{-}$ , ${\mathrm{SO}}_4^{2-}$ , ${\mathrm{NH}}_4^{+}$ and secondary organic carbon (SOC). PAHs in the particles were mainly 4-6 rings, and the heavy metals were mainly Zn and Mn.About 50%-95% of water-soluble ions, 43%-93% of PAHs and 44%-97% of seven heavy metals in the four functional areas were concentrated in PM_2.5. The chemical components of particulate matter in different functional areas featured in their own chemical characteristics. Higher fractions of water-soluble ions were observed for ${\mathrm{NO}}_3^{-}$ at West 3-Ring Road, Cl^- and ${\mathrm{NH}}_4^{+}$ at Huayuan North Road, ${\mathrm{NH}}_4^{+}$ at Changping countryside and Ca²⁺ at Milu Park. In addition, greater fractions of particulate matters were found for PAHs in Huayuan North Road, and Ni and PAHs in Changping rural site. During the sampling period, the major sources contributing to PM₁₀and PM_2.5 were coal combustion, mobile and secondary sources, as well as biomass sources.