The objective of this study is to investigate the potential pollution sources of PM2.5 in Kaohsiung and Pingtung with the isotopic fingerprints. During the period from the spring (March) of 2020 to the summer (August) of 2020, ambient PM2.5 samples were collected from 8 sampling stations (Ciaotou, Zuoying, Fengshan, Siaogang, Daliao, Linyuan, Pingtung, and Chaozhou) in Kaohsiung and Pingtung, respectively. In addition, we also collected PM2.5 samples from 5 specific sources: a coal-fired power plant, an incinerator, an oil refinery plant, a plastic factory, and a paper-making factory in 2020. All the PM2.5 samples were characterized with the measurements of water-soluble ions, organic carbon, elemental carbon, crustal elements, heavy metals, and isotopic compositions of carbon (δ13C and 14C) and lead (206Pb, 207Pb, and 208Pb).
The results revealed that condensable particulate matter (CPM) was predominant particles in the PM2.5 emitted from stationary pollution sources. Moreover, the level of inorganic CPM was higher than that organic CPM in all stationary pollution sources. The chemical compositions from five pollution sources were: (1) coal power-fired plant: sulfate was important specie, predominant elementals included Mg, Ni, Cu, Zn, Mo, Cd, Sn, Sb, Tl, Pb, Cr, As, Y, Se, Ge, and Ga, average 206Pb/207Pb and 208Pb/207Pb were 1.2430 (1.1759-1.3056) and2.4507 (2.4373~2.4796), respectively; (2) incinerator: sulfate, Ca+2, and Cl- were important species, predominant elementals included Na, K, Ca, Ba, Co, Ni, and Zn, average 206Pb/207Pb and 208Pb/207Pb were 1.1479 (1.1439-1.1522) and 2.4281 (2.4217~2.4365), respectively; (3) oil-refinery plant: EC, sulfate, and Ca+2 were important species (69%), predominant elementals included Na, Ni, Zn, Mo, Cd, Sn, Sb, and Se, average 206Pb/207Pb and 208Pb/207Pb were 1.2663 (1.2200-1.3070) and 2.4206 (2.4113-2.4259), respectively; (4) plastic factory: sulfate was important species (31%), predominant elementals included Co, Ni, Cu, Zn, Mo, Cd, Sn, Tl, Pb, Cr, As, and Se, average 206Pb/207Pb and 208Pb/207Pb were 1.1715 (1.1594-1.1847) and 2.4241 (2.4198-2.4282), respectively; (5) paper-making factory: sulfate and Ca+2 were important species (10%), predominant elementals included Ni, Zn Cd, Sn, Sb, and Se, average 206Pb/207Pb and 208Pb/207Pb were 1.2067 (1.1713-1.2342) and 2.4336 (2.4308-2.4359), respectively.
The average level of ambient PM2.5 from all sampling sites was 20.1 ± 11.3 μg/m3, which lower than national standard (35 μg/m3). The major constituents of the ambient PM2.5 in the study area included sulfate, nitrate, ammonium, and organic carbon, which accounted for 19%, 24%, 14%, and 24% of the PM2.5 mass, respectively. The contributions of fossil (16%) and modern (14%) carbon were similar in the six sampling sites in Kaohsiung. Modern carbon was a predominant carbonaceou aerosol in Pingtung and Chaozhou sampling sites (modern carbon: 15%; fossil carbon: 14%). It was found from the chemical analysis that the concentrations of inorganic secondary aerosols (sulfate, nitrate, and ammonium) and fossil/modern carbonaceous aerosols were elevated during high PM2.5 episodes. These results implied that photochemical reactions and burning activities of fossil/modern carbon were important factors influencing the PM2.5 in the study areas.
The averages of δ13C for ambient PM2.5 are -25.7‰ (-34.0 to -21.0‰) and -28.3‰ (-38.2 to -20.3‰) in the spring and summer, respectively. The average 206Pb/207Pb ratios were 1.1493 (1.1021-1.1581) and 1.1525 (1.0897-1.2081) in the spring and summer, respectively, and 208Pb/207Pb ratios were 2.4251 (2.3768-2.4393) and 2.4247 (2.3677-2.4570), respectively. The variation of δ13C and Pb isotopic compositions were larger, which means the pollution sources were unstable in Kaohsiung and Pingtung for carbon and Pb. In comparison, the values of isotopic compositions were similar to the data in central Taiwan, which reflects the pollution sources and influencing factors were different according to different locations in Taiwan.
In this study, we combined with the traditional chemical and isotopic compositions of ambient and pollution sources to investigate the pollution sources for PM2.5 in Kaohsiung and Pingtung. Our results indicated that biomass burning, oil-combustion, and nitrate (secondary aerosol) were major pollution sources for carbon. In the Zuoying, Fengshan, Linyuan, and Siaogang stations, fossil carbon burning was an important contrubtor; in the Pingtung and Chaozhou stations, modern carbon burning plays an important role. In the Ciaotou and Daliao stations, we need more information to investigate completely the potential sources for the both sties due to unstable of carbon pollution sources on different seasons. Based on the PMF model and Pb isotopic compositions, traffic emission, oil-combustion, Kaohsiung port activities, and incinerator were major pollution sources for Pb in the Kaohsiung and Pingtung.