The objective of this study is to investigate the compositions of carbon and lead isotopes in fine particulate matters (PM2.5) and, accordingly, to attribute potential sources of PM2.5 in Kaohsiung and Pingtung with the isotopic fingerprints. During the period from the spring (March) of 2019 to the summer (July) of 2019, ambient PM2.5 samples were collected from 8 sampling stations (Ciaotou, Zuoying, Fengshan, Siaogang, Daliao, Linyuan, Pingtung, and Chaozhou), respectively. In addition, this study also collected PM2.5 samples from 4 specific sources: a coal-fired power plant, an oil refinery plant, a steel plant, and Kaohsiung port in April and August, respectively. 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 in the PM2.5 emitted from three stationary pollution sources. Moreover, the level of organic CPM was higher than inorganic CPM in oil-refinery plant, whereas the levels of inorganic CPM were higher in both coal-fired power plant and steel plant. The chemical compositions from four pollution sources were: (1) coal-fired power plant: sulfate was important species (10%), predominant elementals included Na (due to the flue gas desulfurization with seawater), Mg, K, Ni, Zn, Mo, Cr, and Se, average 206Pb/207Pb and 208Pb/207Pb were 1.1959 (1.1781~1.2115) and 2.4305 (2.4108~2.4403); (2) oil-refinery plant: sulfate was important species (54%), predominant elementals included Fe, Mn, Ni, Zn, Mo, Pb, and Cr, average 206Pb/207Pb and 208Pb/207Pb were 1.1930 (1.1759~1.2106) and 2.4318 (2.4171~2.4437); (3) steel plant: sulfate was important species (35%), predominant elementals included Fe, Mg, K, Ca, Mn, Zn, Mo, Cd, Tl, Pb, Cr, Se, Rb, and Cs, average 206Pb/207Pb and 208Pb/207Pb were 1.1908 (1.1664~1.2143) and 2.4010 (2.3774~2.4229), the percentage of modern carbon was 18% (14~22%); (4) Kaohsiung port: the major compositions included sulfate, nitrate, ammonium, organic carbon, and elemental carbon, predominant elementals included Na, Zn, and V, δ13C ranged from -31.3 to -22.5‰, average 206Pb/207Pb and 208Pb/207Pb were 1.1561 (1.1406~1.1884) and 2.4295 (2.4013~2.4546), the average percentage of modern carbon was 34% (12~68%).
The average level of ambient PM2.5 from all sampling sites was 19.9 ± 10.2 μg/m3, which was lower than national air quality standard (35 μg/m3). The major constituents of the ambient PM2.5 in the study area included nitrate, sulfate, ammonium and total carbon, which accounted for 21%, 20%, 13%, and 24% of the PM2.5 mass, respectively. The contributions of fossil (15%) and modern (14%) carbon were similar in the six sampling sites in Kaohsiung. However, modern carbon was predominant in Pingtung and Chaozhou, which means that investigating and controlling the sources of modern carbonaceous aerosols is helpful to improvement of air quality in that area. It was found from the chemical analysis that the concentrations of inorganic secondary aerosols (sulfate, nitrate, and ammonium) and fossil carbonaceous aerosols were elevated during high PM2.5 episodes. These results implied that photochemical reactions and fossil combustion were important factors influencing the PM2.5 in the study areas.
The averages of δ13C for ambient PM2.5 wee -25.7‰ (-28.2 to -23.6‰) and -25.1‰ (-28.7 to -20.7‰) in the spring and summer, respectively. The average 206Pb/207Pb ratios were 1.1554 (1.1298~1.1712) and 1.1572 (1.0974~1.1966) in the spring and summer, respectively, and 208Pb/207Pb ratios were 2.4263 (2.3985~2.4519) and 2.4295 (2.3741~2.4572), respectively. The variations 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, but, the values were different from that in northern Taiwan, which reflects that there was spatial variation of carbon and Pb pollution sources in Taiwan.
In this study, we combined the traditional chemical and isotopic compositions to investigate the air pollution sources for Kaohsiung and Pingtung. Our results indicated that industrial emission and oil-combustion were important pollution sources. However, it’s necessary to collect more isotopic fingerprints from various pollution sources of PM2.5 for pollution source forensics in the near future, particularly in Pb; moreover, modern carbon was a major component in Pingtung, it’s necessary to deeply investigate the carbon pollution source.