SUN+Jun-ling

Abstract In January 2008， PM10 were sampled concurrently at five contrasting sites： two urban sites （the east gate of China university of Geosciences and the roof of a building within China university of Geosciences）， two industrial sites （Coke-oven plant of Capital steel plant and a thermoelectric plant）， and a background site （Shi San Ling） in Beijing， China. The concentration and spatial distribution of 19 polychlorinated biphenyls （PCBs） congeners were analyzed with isotope dilution and high-resolution gas chromatography/high-resolution mass spectrometry （HRGS/HRMS） based on US EPA 1668A method. Average PM10 concentration was 184?g/m3， which was 22.6% higher than the second-class daily average standard （150?g/m3）， suggesting very serious pollution.The concentrations （∑PCBs） varied from 8.4 to 19.7 pg/m3 with an average concentration of 14 pg/m3， and the toxic equivalent （∑TEQ） ranges from 8.8 to 19.8 fgWHO-TEQ/m3 with a mean value of 15.14 fgWHO-TEQ/m3. PCBs levels were lower in Beijing compared to other metropolises all over the world. The aim of this work was to better understand the overall PCBs levels and identify the source of PCBs in Beijing. We tried to provide solid foundation for preventing pollution from persistent organic pollutants （POPs） in the atmosphere.

Polychlorinated biphenyls （PCBs） are widely spread in the atmosphere， and they are a kind of persistent organic pollutants. They possess characteristics of persistence， toxicity， bioaccumulation and long-distance mobility， which impose serious threat to human health and ecosystems [1]. In recent years it has drawn great attention from the international community. PM10 is referred to the particulates with aerodynamic diameters of less than 10 μm. The atmosphere transportation is the main migration pathways for the environmental pollutants [2-4]. As an important medium in the air， PM10 plays an important role in the diffusion of PCBs in the environment， which has caused severe PM10 pollution and brought great harm to human health. It is of great significance for the environmental protection to study the concentration， spatial distribution and migration behavior of PCBs in PM10.

1 Experimental details

PM10 were sampled concurrently at five contrasting sites： two urban sites （the east gate of China university of Geosciences and the roof of a building within China university of Geosciences）， two industrial sites （Coke-oven plant of Capital steel plant and a thermoelectric plant）， and a background site （Shi San Ling） in Beijing， China using glass fiber films （GFFs）. The procedure lasts for 8 days with an interval of 24 h. Before sampling， GFFs were calcined in a muffle furnace for 12 h at 450 ?C and sealed in the aluminum foil to remove the organic matter. The samples were kept in the balance room for 24 h， and their weights were measured using the balance to obtain the concentration of PM10. After the sampling and weighing， 27 types of 13C were added into the GFFs to label the PCBs， and a solvent of n-hexane/dichloromethane （1：1） was used to accelerate the extraction process. After separation by rotary evaporation， the samples went through a composite column of silica gel， concentrated alkaline alumina column and Florida soil column purification. After the nitrogen blow and condensation， 13C labeled PCBs was set to be a standard sample. After the turbine mixing， 13C - PCB - 9， 52， 101， 138 and 194， were examined by high resolution gas chromatography/high resolution mass spectrometry （HRGC/HRMS）. In this paper， we examined 19 kinds of PCBs， including 12 types of DL - PCB#77， 81， 105， 114， 118， 123， 126， 156， 157， 167， 169 and 189， and 6 kinds of indicators such as PCB# 28， 52， 101， 138， 153， 180 and PCB - 209. All solvents are classified as pesticide residues.

Both experimental and field blanks were analyzed. The main interference comes from PCBs# 28， but its concentration is less than 5% of PCBs in the corresponding atmosphere. The average recovery of 13C-labelled PCBs was 78%， conforming to the requirement of US EPA 1668A.

2 Results and Discussion

Figure 1 presents the mass concentration of PM10 in air at different collection sites. The daily concentration of PM10 ranges from 140 μg/m3 to 264 μg/m3， and the average concentration is 184 μg/m3. Compared with the national second-class standard issued by China in 1996 （150 μg/m3）， only the sample from site B in the five sampling sites can meet the standard， and the samples from the other three sites exceed the standard by 13 - 76% with an average of 22.6%. The pollution in Shougang region is most serious， 1.75 times the national second-class standard. Although the background points fall within the national standard limit， but only 6.67% better than the control standard. Compared with other cities in China， PM10 pollution of Beijing is in the medium level. However， when compared with foreign cities Beijing is among the high pollution level. The mass concentrations of PM10 are different for different sites. characterized by industrial zone > downtown （road） > background point， consistent with the results from Wang et al. [5] and Zhao et al.[6]. This fully reflects the characteristics of local emission source. The factors influencing the concentration of PM10 particulates in Beijing include the degree of pollution emission， and the local meteorological conditions. The mass concentration of PM10 decreases with the increasing temperature， and the larger wind speed. In addition， mass concentration of PM10 increases with the increase of relative humidity. However， the concentration and relative humidity is no longer relevant when the humidity increases to a certain degree because of the gravity sedimentation.

The concentrations （∑ PCBs） range from 8.4 to 19.7 pg/m3， with an average of 14.0 pg/m3. The toxicity equivalent of PCBs is calculated according to toxic factor from the world health organization （WHO - TEF） [7]. The toxicity equivalent of PCBs in PM10 ranges from 8.8 to 19.8 fgTEQ/m3， with a mean value of 15.14 fgTEQ/m3. Compared with other regions and countries， the PCBs pollution in Beijing is at a lower level. The concentrations differ from different sampling sites， i.e. industrial zone > downtown （main traffic artery） > background points. Shougang has the highest concentrations of PCBs. The combustion of solid fuel produces a large amount of PCBs mainly composed of low chlorinated homolog [8]. The combustion of liquid fuel is also an important emission source of the PCBs [9]. The selected industrial zone contains many enterprises， and consumes plenty of coal. For example， Shougang is the largest steel enterprise in China， and coal-burning pollution is very serious. Although there is no coal pollution for the traffic roads， exhaust pollution from the motor vehicles and automobile is serious， and at the same time， the contribution of fuel heating to the PCBs is also very big. The background points are away from the traffic road， and coal combustion is lower than the industrial zone， so the pollution of PCBs is relatively light. The concentrations of PCBs of two downtown points are very close because the air circulation is fast， making the PCBs of two sites fully mixed.

The mass concentration of PM10 is an important indicator to evaluate the air pollution. Its concentration directly affects the distribution of pollutants in the air. In the present study， the change trend of PCBs congeners concentration is consistent with the mass concentration of PM10 from each sampling point （Figure 3）， and possible sources of PCBs and PM10 are similar because the combustion is an important source of PM10 [10]. Therefore， the PCBs in Beijing might mainly come from human combustion source such as car exhaust， industry and heating coal， fuel oil， etc.

It has already been pointed out that the fuel combustion produces a large number of PCBs， which mainly contains low chlorinated homologue. According to the chloride analysis， it is found that PCBs in the PM10 from all sampling points are mainly composed of low homologue of 3-6 chloride （five chlorinated highest， followed by trichloride）， similar to the results of other researchers [11， 12]， further illustrating that the PCBs in Beijing mainly come from the fuel combustion process. But Li et al. [13] and Yeo et al. [14] showed that the PCBs are mainly high chlorinated. This discrepancy might be caused by the different emission sources and different meteorological conditions. Because the concentrations of PCBs are not only influenced by emission source， but also controlled by to climatic conditions. By comparing the concentrations of PCBs under different temperatures at the same place， it is found that with the increase of temperature the concentration of low chlorinated PCBs gradually decreases， while the concentration of high chlorinated PCBs with changing temperature is relatively stable. This is because the low chlorinated PCBs with low vapor pressure are easy to transform from particle phase into the gas phase at a high temperature， and high chlorinated PCBs with high vapor pressure is not easy to evaporate at high temperatures.

Through the examination of toxic equivalent ∑ TEQ of 12 kinds of DL - PCBs （Figure 2）， it shows that ∑ TEQ and ∑ PCBs have the same changing trend for five sampling points. The ∑ TEQ is highest for Shougang， 2.2 times the background point， and the second is the power plant， 2.0 times the background point， and the third is east gate of geological university， 1.7 times the background point. This illustrates that apart from combustion， industrial steel iron and steel-melting furnace， the oil of power transformer and the lubricants of motor vehicle on urban traffic roads are all potential source of PCBs [15]. Figure 4 illustrates that the TEQ for PCBs congeners from all sampling points has a similar change trend. PCB - 126 makes biggest contribution to ∑ TEQ， with the average contribution rate of 97%， and PCB - 118 ranks the second， but far lower than the contribution of PCB – 126. Therefore， the biological toxicity of PCB - 126 cannot be ignored.

careful examination of the relative concentration distribution， it is found that PCB – 28 has the highest concentration， similar to the results of Liu et al. [16]. The PCB - 28 was also monitored in other regions such as Spain [17] and Germany [18]. Among the 12 kinds of DL – PCBs， PCB - 118 has the highest concentration， consistent with the results of Liu et al. [19]. The same results come from Taiwan [20] and Shanghai [21]. The average ∑ Indicator PCBs / ∑PCBs of PM10 is at the same level with the results of Liu et al. [22]. Sweetman and Jones [23] proposed that atmospheric migration is a major source of PCBs because the half-life of PCBs in the atmosphere is about 2-6 years. The above facts conform to migration patterns through sediment into soil and the effect of the global distillation. The concentration of low-chlorinated PCB – 28 symbolizing the combustion source in all sampling points ranks the first place， indicating that combustion is an important source of PCBs in Beijing.

3 Conclusions

1） The PM10 pollution in Beijing is quite serious. The daily average of PM10 is 22.6% higher than that of national second-class standard （150 μg/m3）， and the main source of PM10 in Beijing comes from human sources such as fossil fuels in the industrial production， transportation and daily life.

2） Compared with other cities， PCBs pollution in PM10 of Beijing is at a low level. Concentration of PCBs in PM10 ranges from 8.4 to 19.7 pg/m3， and the average is 14 pg/m3. The toxic equivalent ranges from 8.8 to 19.8 fgWHO-TEQ/m3， with a mean value of 15.14 fgWHO-TEQ/m3.

3） PCB - 28 has the highest concentration. Among the 12 kinds of DL – PCBs， PCB- 118 has the highest concentration， but PCB- 126 makes the biggest contribution to the toxic equivalent. The PCB congeners are mainly low-chlorinated Tri – HxCBs. The PCBs mainly comes from the burning of fossil fuels， industry， hot working process （e.g.， steelmaking furnace） and the usage of materials containing PCBs such as transformer oil and lubricating oil for motor vehicles.

4） PCBs can accumulate in PM10 because PM10 particulates are small， and are easy to enter the body through respiratory tract and to deposit in the lung of deep， which can cause great harm to human body. Its monitoring and control need to be strengthened. The source of the PCBs and environment behavior in the atmosphere needs to be further studied.

Acknowledgements

This work was financially supported by the national natural science foundation of China （40475049） and the Beijing natural science foundation of China （8032012）.

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