Pollution characteristics and sources of PM_2.5-bound polycyclic aromatic hydrocarbons during heating season in a district of Beijing, China, 2016

Objective To investigate the pollution characteristics and identify the sources of PM_2.5-bound polycyclic aromatic hydrocarbons (PAHs) on heavily polluted days and non-heavily polluted days during the heating season in a district of Beijing, China in 2016.

Methods PM_2.5 samples were collected for 42 consecutive days from December 30, 2016 to February 9, 2017, and high-performance liquid chromatography (HPLC)was used to measure the concentration of PM_2.5-bound PAHs of the samples. The pollution characteristics of PM_2.5-bound PAHs were compared between heavily polluted days and non-heavily polluted days, and the characteristic ratio method was used to preliminarily identify the sources of PAHs in PM_2.5.

Results During sampling, the median(P₂₅, P₇₅)of mass concentration was 78.23(50.05, 218.93)μg/m³ for PM_2.5 and 58.06(25.23, 112.13)ng/m³ for PM_2.5-bound PAHs. The medians of mass concentrations of PM_2.5 and PM_2.5-bound PAHs on heavily polluted days were 3.94 and 2.89 times higher than those on non-heavily polluted days, respectively. On both heavily polluted days and non-heavily polluted days, fluoranthene, benzobfluoranthene, and pyrene had the highest proportion among PAHs, accounting for 50% in total, followed by BaP, accounting for 10%. Four-ring PAHs had the highest proportion of 50.5%±9.2%, followed by five-ring PAHs (34.5%±7.2%) and six-ring PAHs (15.0%±3.7%). There was no significant difference in the distribution of PAHs components and PAHs with different numbers of rings between heavily polluted days and non-heavily polluted days. The mean of characteristic ratios of four-ring PAHs/(five-ring PAHs+six-ring PAHs), BaP/BghiP, Ind/(Ind+BghiP), FlT/(FlT+Pyr), and BaA/(BaA+Chr) were 1.08, 1.56, 0.53, 0.58, and 0.49, respectively, that indicated PAHs mainly came from local sources of coal/biomass combustion and traffic emission.

Conclusion There was a relatively high pollution level of PM_2.5-bound PAHs in the district of Beijing during the heating season in 2016, and coal combustion and vehicle exhaust were the main sources of PM_2.5-bound PAHs. It implied that surrounding residents should take good personal health protection measures during the heating season.