| Objective:This study focused on the pollution characteristics of Traffic related PM2.5, chemical speciation and bioavailability of heavy metals as well as carbon aerosols in atmospheric PM2.5 in a District of Taiyuan City. It can provide a scientific basis for prevention and control of atmospheric pollution in Taiyuan City.Methods:PM2.5 concentration was measured by weight method. Total concentration and chemical speciation of five heavy metals in PM2.5 were determined by electric heating board digestion method and sequential extraction procedure, respectively.The bioavailability of heavy metals was determined by the biological effectiveness coefficients resulting from their chemical speciation. Both the concentrations of organic carbon（OC）and elemental carbon（EC） in PM2.5 were determined by thermal light method.Results:1. In this study, the PM2.5 concentrations of four seasons in Taiyuan City decreased in the following order: winter（212.81±78.72 μg/m3）>Spring（168.23± 21.99 μg/m3）>Summer（156.08±48.37 μg/m3）>Autumn（122.08 ± 55.97 μg/m3）.The daily average of PM2.5 rangedfrom 122.08 to 211.81 μg/m3, which was much higher than that（75 μg/m3） in the new national standard.2. The concentrations of five heavy metals in PM2.5 showed seasonal variations. The concentrations of Cr in summer and autumn were higher, while the concentrations of Pb and Cd in winter were the highest. The variations of the concentrations of Cu and Ni during four seasons were not obvious.3. There were significant differences between different chemical fraction distributions of five heavy metals in PM2.5. More than 75% of Pb and Cd were mainly associated with the soluble and exchangeable fraction and carbonate, oxide and reducible fraction, while Ni and Cr were predominantly bound to the organic matter, oxidisable and sulphidic fraction and residual fraction. The organic matter, oxidisable, and sulphidic fraction as well as residual fraction of Cu was found to be the highest among spring, summer, and autumn,while the carbonat, oxide, and reducible fraction as well as organic matter, oxidisable, and sulphidic fraction of Cu in winter was higher than other chemical fractions.4.The bioavailability of five heavy metals decreased in the following order: Cd>Pb>Cu>Ni>Cr. This indicated that both Cd and Pb were classified as the bioavailable elements, while Cu, Ni, and Cr were remarked as the potential bioavailable elements.5.The OC and EC concentration of four seasons decreased in the following order:winter>spring>autumn>summer.6. There was significant correlation between the OC and EC in PM2.5 in four seasons.This indicated the OC and EC had similar sources. Besides, the correlation coefficient of OC and EC between summer and autumnwas higher than that between winter and spring. Due to OC/EC>2 in four seasons, the secondary organic carbon existed in PM2.5.The concentration of OC/EC four seasons decreased in the following order: winter>spring>summer>autumn.7. SOC was an important part of OC. And the proportion of four seasons ordered as follows: winter > spring > summer>autumn.Conclusion:1. The Traffic related PM2.5 pollution of Taiyuan City is serious and shows significant seasonal variations.2. The concentrations of five heavy metals（Cd,,Cr,Cu,Ni,Pb） in Traffic related PM2.5has seasonal variations. The pollution levels of Cr and Cd exceed seriously. There are significant differences between different chemical fraction distributions of five heavy metals in PM2.5. Cd and Pb are classified as the bioavailable elements, while Cu, Ni, and Cr are remarked as the potential bioavailable elements.3. The percentage of OC to TC is higher and has seasonal variation. There are different levels of secondary pollution in different sampling periods. The secondary pollution in winter is more serious than that in other seasons. |
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