Characteristics of PM2.5 and its chemical constituents in Beijing, Seoul, and Nagasaki

Ambient fine particulate matter (PM 2.5 ) samples were collected from September 2013 to May 2015 in three cities in East Asian countries (Beijing, China; Seoul, South Korea; and Nagasaki, Japan) in order to analyze the spatiotemporal trends of PM 2.5 chemical constituents including organic matter (OM), elemental carbon (EC), water-soluble inorganic ions (NO 3 − , SO 4 2− , and NH 4 + ), and trace elements. The average PM 2.5 mass concentration were 125 ± 6.80 μg m −3 , 44.6 ± 0.84 μg m −3 , and 17.4 ± 0.37 μg m −3 in Beijing, Seoul, and Nagasaki, respectively. Higher carbonaceous concentrations were observed during winter in Beijing and Seoul, while higher concentrations were found during spring in Nagasaki. The highest seasonal averages of organic carbon (OC) to EC ratios were found during spring in Beijing, winter in Seoul, and fall in Nagasaki. The concentrations of secondary OC and its ratio to OC were high during fall and winter. For ion species, NO 3 − was dominant in Beijing and Seoul, while SO 4 2− was dominant in Nagasaki. Increased contributions of mobile sources in Beijing and Seoul were observed, with higher NO 3 − /SO 4 2− ratios than those in Nagasaki. Three groups of air masses were found for the three cities using cluster analyses based on 72-h backward trajectories. The cluster from the Bohai economic zone had the highest concentration of PM 2.5 for Beijing. For Seoul, a cluster that originated from the Yellow Sea near an industrial area in Liaoning Province and passed through a highly polluted industrial area in southwestern Seoul had high PM 2.5 concentrations. A long-range transported cluster that originated in and crossed through heavily industrialized areas in China and South Korea for Nagasaki had higher ion species concentrations. The results of this study are useful to identify the current levels of PM 2.5 and its chemical properties to establish a control plan for PM 2.5 for Northeast Asia, including China, South Korea, and Japan.