Seasonal and spatial variation of trace elements in multi-size airborne particulate matters of Beijing, China: Mass concentration, enrichment characteristics, source apportionment, chemical speciation and bioavailability

Atmospheric Environment 99 (2014) 257e265

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Seasonal and spatial variation of trace elements in multi-size airborne particulate matters of Beijing, China: Mass concentration, enrichment characteristics, source apportionment, chemical speciation and bioavailability Jiajia Gao a, Hezhong Tian a, *, Ke Cheng a, Long Lu a, Yuxuan Wang b, Ye Wu c, d, Chuanyong Zhu a, Kaiyun Liu a, Junrui Zhou a, Xingang Liu a, Jing Chen a, Jiming Hao c, d a

State Key Joint Laboratory of Environmental Simulation & Pollution Control, School of Environment, Beijing Normal University, Beijing 100875, China Ministry of Education Key Laboratory for Earth System Modeling, Center for Earth System Science, Tsinghua University, Beijing 10084, China c School of Environment, Tsinghua University, Beijing 10084, China d State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing 100084, China b

h i g h l i g h t s
Daily TSP/PM10/PM2.5 samples are collected in four seasons at four sites in Beijing.
19 elements in multi-size PM are analyzed for characterization of Beijing aerosol.
Soil dust, coal burning, and traffic exhausts represent the dominant sources of PM.
Toxic elements (As, Cr, Ni, etc.) exhibited high bioavailability in PM10 and PM2.5.
Special concern should be paid to toxic trace elements for policymaking in Beijing.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 28 April 2014 Received in revised form 22 July 2014 Accepted 11 August 2014 Available online 2 October 2014

The seasonal and spatial variation characteristics of 19 elements (Al, As, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, S, Sb, Se, Zn) in TSP/PM10/PM2.5 samples were investigated, which were collected from April 2011 to January 2012 simultaneously at an urban downtown site, a traffic roadside site, a suburban site, and a rural site in Beijing. The elevated concentrations of several toxic trace elements (As, Cd, Mn, Ni, Pb, etc.) in particles revealed that the contamination of toxic elements in Beijing could not be neglected. Positive matrix factorization method (PMF) was applied for source apportionment of trace elements in PM, and three factors (crust related sources, combustion sources, and traffic and steel industrial related sources) were identified. Furthermore, the chemical speciation and bioavailability of various elements were identified by applying European Community Bureau of Reference (BCR) procedure. Our results showed that eight toxic elements (As, Cd, Cr, Cu, Ni, Pb, Sb and Zn) exhibited higher mobility in PM2.5 than in PM10. Notably, elements of As, Cd, Pb and Zn were presented with higher mobility than the other elements, and these elements were lightly to release into the environment and easily available to human body. Additionally, As, Cd, Pb and Zn also accounted for higher percentages in the bound to mobile fractions at the central urban areas of Beijing. Therefore, special concerns should be paid to these toxic trace elements which had relatively high mobility in fine particles, when planning and implementing the comprehensive air pollution mitigation policies in Beijing. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Atmospheric aerosol Trace elements Positive matrix factorization (PMF) Enrichment factor (EF) Chemical speciation

1. Introduction

* Corresponding author. E-mail addresses: [email protected], [email protected] (H. Tian). http://dx.doi.org/10.1016/j.atmosenv.2014.08.081 1352-2310/© 2014 Elsevier Ltd. All rights reserved.

It is widely accepted that atmospheric particulate matter (PM) is harmful for human health with regard to respiratory and cardiovascular diseases, morbidity, and mortality (WHO, 2001). Epidemiological studies indicated that the morbidity of lung cancer in

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human beings was closely related to the pollution level of total suspended particles (TSP) in urban atmospheric environment (Wang, 2002). Acute and chronic exposures to ambient PM were also closely associated with the aggravation of asthma and the high incidence of chronic obstructive pulmonary disease (Wang et al., 2013). Normally, multiple elements exist in the particulate phase in the air. In many of the metropolis, large amounts of PM are released from natural sources (e.g. soil dust, volcanism, erosion, surface winds and forest fires) and anthropogenic sources (e.g. fossil fuel combustion, industrial metallurgical processes, vehicle emissions and waste incinerations) (Manalis et al., 2005; Valavanidis et al., 2006; da Silva et al., 2008; Tian et al., 2011, 2012a, b). Dust-soil, industry emission, coal burning, vehicle exhaust emission and waste incineration are thought to be the major sources of particulate pollution at Beijing (Sun et al., 2004). Beside the total mass concentrations of PM, the chemical compositions of PM especially some toxic trace elements (As, Cd, Cr, Ni, Pb, etc.) that absorbed on PM play a crucial role in assessing atmospheric PM pollution and its hazards to human health (Chillrud et al., 2004). Furthermore, in order to assess the possible health impacts, it is vital to be acquainted with not only the total amounts of toxic elements, but also their chemical speciation and bioavailability. It is necessary to quantify the specific metallic forms since solubility, bioavailability, geochemical transport and metal biogeochemical cycles largely depend on physicalechemical speciation (Richter et al., 2007). Beijing is the capital city of China with a population of approximately 19.6 million and annual coal consumption of 26 million tonnes in 2010 (NBS, 2011a, b). It has been confronted with a serious complex air pollution problem (Okuda et al., 2008; He et al., 2009; Song et al., 2012; Zhou et al., 2012). Previous studies investigated the characteristics of aerosols in Beijing, and several methods have been used for source identification and apportionment of PM including enrichment factor (EF), principal component analysis (PCA), chemical mass balance (CMB) and positive matrix factorization (PMF) (Sun et al., 2004; Okuda et al., 2004; Duan et al., 2012; Zhang et al., 2013). Nevertheless, most of these studies mainly targeted to the bulk mass concentration, conventional major chemical composition characterization of PM, or its source apportionment in a single sampling point. In this study, instead of the conventional analysis on ions composition and organic/ elemental carbon in PM, we mainly focused on investigation of the seasonal and spatial pollution characteristics of various trace elements especially some trace heavy metals and metalloids in multisize particles, as well as the enrichment features, source apportionment and bioavailability of several toxic trace elements, such as As, Cd, Cr, Ni and Pb. 2. Experimental section 2.1. Study area and sampling sites details Beijing city is geographically located at 39 560 N and 116 200 E on the northwestern edge of the North China Plain, surrounded by the Taihang and Yanshan Mountains in the west, north, and northeast. The four seasons of Beijing are mainly characterized by variable meteorological conditions: spring featured by high-speed winds and low precipitation, summer by high temperature and frequent rain usually accounting for 75% of annual rainfall, autumn by sunny days and northwest winds, and winter by cold and dry air (Zhang et al., 2013). TSP, PM10 and PM2.5 samples were simultaneously collected at four sampling sites with consecutive days during four selected months (April, August, October 2011 and January 2012), which

representing four seasons in Beijing: (1) Beijing Normal University campus (urban downtown site, BNU, A), (2) the 4th north ring roadside (traffic roadside site, B), (3) Daxing district (suburban site, C), and (4) Miyun county (rural and background site, D). The details and location of each sampling site were presented in SI Table S1 and Fig. 1. TSP, PM10 and PM2.5 were simultaneously collected on quartz filters (Pallflex Tissuquartz™, 90 mm, USA) over a period of 24 h each day with TH-150C medium volume air samplers (Wuhan Tianhong Instruments Co., Ltd., flow rate: 100 L/min). The filters with PM samples were covered by tin paper and put into a refrigerator in which the temperature was kept at about 20  C for disposal when the sampling was finished. Totally 335 effective samplings were collected and analyzed. For comparison and validation, we referred to the daily average PM10 concentrations which were released on the website of the Beijing Environmental Protection Bureau (BJEPB, 2012a) and represented the mean concentrations of PM10 at multiple observation points in Beijing. We found that there was a good relevance between the daily average PM10 concentrations observed at our four sampling sites and those reported by BJEPB (R2 ¼ 0.654, n ¼ 77) (see SI Fig. S1). Thus, to a certain extent, the data obtained from this field-test campaign were thought to be effective and reasonable on behalf of the seasonal and spatial characteristics of trace elements in PM pollution of Beijing. 2.2. Analytical procedures 2.2.1. Mass concentrations After weighting, the aerosol-loaded filters were placed in Teflon tubes and each filter was digested with a 3:1:1 mixture of HNO3HClO4-HF in Teflon vessels and heated in a microwave system. Then, the digested solution was diluted to 10 mL, totally 19 trace elements (Al, As, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, S, Sb, Se and Zn) were measured by using inductively coupled plasma atomic emission spectrometry (ICP-AES, SPECTRO Analytical Instruments GmbH, SPECTRO ARCOS EOP). ICP-AES were calibrated by an external calibration method. Calibrants were prepared from multi-element standard solution (50 mg/L, Teknolab A/S, Norway). Standard Reference Material, SRM 1648 ‘Urban Particulate Matter’, from the National Institute of Standards and Technology (Gaithersburg, MD, USA) was used to validate the methods. The SRM was treated in the same manner as the samples. Reagent blanks and filter blanks were also routinely analyzed in between samples to check for contamination. 2.2.2. Source appointment Enrichment Factor (EF) method with Al as the reference element was used to assess the enrichment characteristics of various trace elements in multi-size PM. EF of each element which was calculated relative to the average crustal rock composition (Mason and Moore, 1982) with Al as the reference element: EF ¼ (X/Al)Aerosol/ (X/Al)Crust. Then, in order to identify the possible major sources, positive matrix factorization (PMF) method was adopted to conduct the source identification and apportionment of various elements in PM. PMF model was one of the receptor models developed by the US Environmental Protection Agency (EPA). The algorithms used in PMF model to compute profiles and contributions had been reviewed by previous researchers and were certified to be scientifically robust (Paatero, 2004; Song et al., 2006). The input data of EPA PMF included the concentration of each sample data and the uncertainty of the data, which could be calculated as follows (Polissar et al., 1998):

U ¼ 5=6  MDLðc  MDLÞ

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259

Fig. 1. Topographical condition and location of the four sampling sites in the city of Beijing.

U¼

qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðP  cÞ2 þ ðMDLÞ2 ðc > MDLÞ

where U is the data uncertainty; MDL is the minimum detection limit of the instrument; P is expressed as a percentage of the measurement uncertainty; c is the concentration of the sample. P values were set to 10% estimated by experience. The MDLs and percentage of concentrations used in calculating the uncertainties by EPA-PMF were illustrated in Table S2. Besides, more detail description about some parameters in the process of EPA PMF 3.0 model operation were briefly provided behind SI Table S2. 2.2.3. Sequential extraction and chemical speciation analysis BCR three-step sequential extraction procedure was applied to analyze the species distribution of various trace elements in multisize PM samples of Beijing. The BCR sequential extraction scheme was put forward by the European Community Bureau of Reference (now the EU Standards Measurement and Testing Program, SM & T) based on Tessier's procedure (Quevauviller et al., 1993), which was the most common and relatively mature method for investigation of the elemental speciation in aerosol at present. The extraction schemes and conditions were listed out in SI Table S3. 3. Results and discussion 3.1. Trace element concentrations in TSP, PM10 and PM2.5 In this study, the annual average concentrations of TSP, PM10 and PM2.5 for the above four sampling sites in Beijing were calculated at

about 205, 144 and 83 mg/m3, slightly exceeded the second grade ceilings of National Ambient Air Quality Standard (NAAQS, GB 3095-1996) annually average value of 200 mg/m3 for TSP and 100 mg/m3 for PM10. However, concentrations of PM10 and PM2.5 were nearly 2.1 times and 2.3 times higher than the second grade of new issued NAAQS (GB 3095-2012) of China, respectively. Also, PM10 concentration in present study was almost the same level in comparison to that released by Beijing Environmental Statement in 2011 (114 mg/m3, BJEPB, 2012b). Furthermore, the mean ratios of PM10/TSP and PM2.5/PM10 in our tests were calculated at about 0.70 and 0.58, respectively, indicating that fine particles contributed significant to coarse particles and more concerted actions ought to do to prevent primary fine particles emissions as well as the secondary fine PM formation pollution. Mass concentrations of totally 19 elements (Al, As, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, S, Sb, Se and Zn) in multi-size PM samples were determined by using ICP-AES. Although only with very low concentrations, some of these trace elements adsorbed on PM were toxic to public health. Table 1 showed the comparison of levels of some toxic elements in PM with the standard limits of NAAQS (GB 3095-2012) in China and World Health Organization (WHO) guidelines. It could be seen that Cd concentration was approaching the limits regulated in the GB 3095-2012 and WHO guidelines; whereas concentrations of As and Mn were substantially higher than the limits in GB 3095-2012 and WHO guidelines. In comparison, Pb and Ni concentrations were a little lower than the GB 3095-2012 and WHO guidelines limit. Moreover, Table 1 also presented concentrations of some toxic

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Table 1 Annual maximum acceptable limits for some toxic elements in TSP in GB 3095-2012, WHO guidelines as well as element concentrations in PM10 from different studies (unit: ng/m3). Elements

GB 3095-2012

As Cd Cr Ni Mn Pb Cu Zn

6 5 0.025 (Cr(VI)) 20 150 500 ee e

a

WHOb

Beijingc

6.6 5 0.25 25 150 500 e e

47.8 4.9 35.2 14.2 166.7 233.9 401.6 683.2

Beijingc

TSP

a b c d e

Beijingd

PM10 ± ± ± ± ± ± ± ±

13.3 0.8 5.4 3.4 44.1 35.1 288.9 120.5

37.7 4.4 33.8 12.7 112.3 208.3 226.8 603.3

± ± ± ± ± ± ± ±

18.1 1.3 2.8 1.8 24.0 32.2 140.7 127.3

41.1 6.8 20.0 15.5 268 400 110 806.0

MEP (2012). WHO (2000). This study. Okuda et al. (2008). not determined.

elements in PM10 of Beijing reported in different studies. It could be seen that As, Cd, Ni, Mn, Pb and Zn concentrations in present study were 8.3%e58.1% lower than those in the year of 2004e2005 in Beijing, while Cr and Cu in our study were 1.9 times and 2.1 times higher than those in 2004e2005 in Beijing. The concentrations of Cr and Cu increased much during the past years might be closely related with the rapid increase of vehicle populations in Beijing as discussion in Section 3.2. Seasonal and spatial distribution characteristics of various elements concentrations in multi-size PM were shown in Fig. 2 and

Fig. 3, respectively. For Al, Be, Ca, Fe, Mg, and Na, the highest concentrations were appeared in spring for each particle size, which could be mainly attributed to high loading of crustal dust due to the low relative humidity and strong wind in spring of north China. Total concentrations of Al, Be, Ca, Fe, Mg, and Na in spring contributed about 79.9%, 69.8%, and 42.4% to the total TSP, PM10, and PM2.5 element concentrations respectively, indicating that Al, Be, Ca, Fe, Mg, and Na would be more likely originated from dust storm and road dust related sources and occurred mostly in coarse particles. While the concentrations of As, Cd, Pb, S, and Se were higher in autumn and winter than those in spring and summer for each PM size fraction. Total mass of these five trace elements in autumn and winter accounted for 27.8%, 33.7% and 54.4% of the whole elements concentrations for TSP, PM10, and PM2.5, respectively, which indicated that As, Cd, Pb, S, and Se could be mainly associated with fuel combustion sources and existed largely in fine particles. A combination of persistent temperature inversions and increases in manmade emissions related to heating in wintertime could partly explain the increases in ambient pollutant concentrations (Duan et al., 2006; Tian et al., 2010, 2012a). Additionally, in our previous study (Tian et al., 2012a), the results of monthly temporal variation characteristics of Cd, Cr and Pb emissions showed that coal consumption of residential and other sectors for supplying heat in winter would increase emissions of Cd, Cr and Pb, which were well accordance with our observations. With regard to the spatial variation, apart from Cr, Cu, Ni, Sb and Zn, concentrations of other targeted trace elements in each size PM were found to be highest at Daxing site and followed by BNU site, 4th ring site, and Miyun site (Fig. 3), which were consistent with

Fig. 2. Concentration of various elements in multi-size aerosols by season, ng/m3.

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Fig. 3. Concentration of elements in multi-size aerosols by functional district, ng/m3.

the overall situation that air quality in north district of Beijing was better than that in central and south district (BJEPB, 2012b). The northern region of Beijing was blocked by mountains and largely covered by agriculture, forest and scenery protection zone, while the southern plain regions were not only densely populated and with more intensive industrial activities, but also were easily affected by the pollutants diffusion and trans-boundary transportation from surrounding cities, such as Tianjin, Langfang, Tangshan and Baoding (see Fig. 1). In comparison, we found that Cr, Cu, Ni, Sb and Zn concentrations in each particle size at the 4th ring site were highest among the four sites. The total concentrations of Cr, Cu, Ni, Sb and Zn at the 4th ring site were about 1.8 times, 1.9 times, 2.2 times higher than those at Daxing site, BNU site, Miyun site for TSP; and were about 1.5 times, 1.4 times, 2.3 times higher than those at Daxing site, BNU site, Miyun site for PM10; and were about 1.3 times, 1.4 times, 2.3 times higher than those at Daxing site, BNU site, Miyun site for PM2.5, respectively. Furthermore, the concentrations of Cr, Cu, Ni, Sb and Zn were found to be significantly correlated (Cr, Cu, Ni and Sb correlated with Zn with coefficients of 0.59, 0.73, 0.62 and 0.78, respectively). The strong correlation among these elements known as traffic-markers (Sternbeck et al., 2002; Iijima et al., 2009; Duan et al., 2012) suggested an intensive impact of the traffic-related sources: exhaust, brake wear, tires, and fossil fuel combustion, as well as the road line paintings and the galvanized security barriers. 3.2. Source identification and apportionment of trace elements in PM In this study, in order to identify whether the presence of a certain element in aerosols was primarily due to natural or

anthropogenic processes, the enrichment factor (EF) of each element was determined. EFs of elements in multi-size particles in Beijing were illustrated in Figs. 4 and 5. The mean EFs of Be, Ca, Co, Fe, K, Mg, Mn, and Na in each particle size samples for the four sampling sites were normally below 10, and the EF values for different samples were relatively constant, which suggested that these elements would be more likely originated from natural sources and had no obvious enrichment in aerosols. In comparison, the average EFs of As, Cd, Cu, Pb, S, Sb, Se, and Zn were in the range of 101 ~ 104, suggesting these elements were mainly originated from anthropogenic sources. Moreover, we found that the EFs of these elements in PM2.5 samples were generally higher than those in TSP and PM10, particularly for the more highly enriched elements like As and Se. Remarkably, the EFs of Cr and Ni for TSP and PM10 were below 10 while they were above 10 for PM2.5, revealing that Cr and Ni were from the “mixed origin” sources. Therefore, Cr and Ni in coarse particles were thought to have more soil-related origins, while Cr and Ni in fine particles were mostly from anthropogenic combustion sources. These findings were consistent with the following PMF results that Ni and Cr for PM2.5 were mainly come from vehicle emissions (Tian et al., 2012c). Notably, no obvious rise was found in the EFs of Pb at the traffic roadside site, which suggested that motor exhaust emissions might not be a major source of Pb in PM of Beijing because leaded gasoline had been phased out since 1997. However, the EFs of Pb for TSP, PM10 and PM2.5 in winter were about 1.4-fold, 1.3-fold and 2.1-fold higher than that in summer respectively, which revealed that coal combustion might be the main source of Pb in winter and was in well accordance with our former results on emission inventory (Tian et al., 2012a). Also, it was worth noting that the EFs of Cu, Zn, Pb, Cd, As, S, Sb, and Se in

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Fig. 4. Average enrichment factor of various elements in aerosols by season in Beijing.

Miyun site for TSP were a little higher than those in the other three sampling sites, and similar characteristics were also found in the study of Zhao et al. (2009). There were no obvious emission sources around Miyun sampling site, and it might be explained by the regional transmission of fine PM enriched with primary pollution elements. Furthermore, EPA PMF 3.0 model was used to evaluate the possible predominant emission sources of various elements in

aerosols of Beijing. The results of PMF 3.0 for TSP and PM2.5 were illustrated in Fig. 6 and Fig. 7, respectively. As shown in Fig. 6, three factors were identified by PMF 3.0 for TSP. Factor 1 (dust), explained 77.0% to total elements, with high loading for Ca (87.3%), Mg (86.9%), Fe (79.0%), and Al (76.6%), suggesting crust related sources, such as road and construction fugitive dust, sand wind, constituent the main sources (Trapp et al., 2010). Factor 2 (combustion), which accounted for 15.0% of species total, were heavily loaded with As (96.8%), Cd (96.8%), Pb (96.0%), Se (95.1%), and S (95.0%). Since As, S, Se were typically come from coal burning, thus, Factor 2 were highly associated with combustion sources especially coal burning. Factor 3 (vehicle) presented 8.0% of total species and had high contribution of Cu (78.0%), Zn (74.6%), and Sb (62.8%), indicating that they were connected with traffic related sources (e.g. brake and tires wear and exhausts emission) (Iijima et al., 2007; Johansson et al., 2009; Tian et al., 2012d). When applying PMF 3.0 to PM2.5, three factors were also retained while they were varied with those for TSP (Fig. 7). Factor 1 (Mixed sources), which explained 65.9% of the total variance, was associated with Se (65.5%), S (61.8%), As (60.4%), Pb (60.0%), Cd (59.9%), and K (52.6%). It might be mixing sources with local and long-distance transmission particles, which included coal burning, biomass combustion and other industries around Beijing city. Tianjin was one of the biggest industrial cities in Northern China and Hebei Province possessed the highest iron and steel production capacity in China; Biomass burning pollution in rural areas of Beijing and Hebei Province was often reported. There results were well accordance with other researchers' results that about 34% of PM2.5 on average could be attributed to sources outside Beijing, and during the eastern and southern wind prevailing period, Hebei Province could contribute 50%e70% of PM2.5 concentrations in Beijing (Streets et al., 2007; Duan et al., 2014). Factor 2 (vehicle and steel industrial sources) showed 26.5% of the total species with high loadings for Ni (91.3%), Zn (62.35%), Cu (51.9%), and Cr (45.65%), it might be likely represent the traffic related source emissions and long-distance transmission particles from iron and steel smelting industries around Beijing. Factor 3 (dust) had high loadings for Ca (93.3%), Mg (90.3%) and Al (87.7%), and it explained 7.6% of the total variance. It could represent the re-suspended road dust and the long-range transported dust from outside of Beijing. In general, it could be concluded that trace elements in aerosols of Beijing came from three main sources: road and construction dust, combustion sources, and traffic related sources. In addition, due to atmosphere transportation, fine particles transportation in long-distance from the surrounding cities might become more significant contribution of the source; straw burning and coal heating in autumn and winter were also important sources (Zhu et al., 2005). With the rapid increase of vehicle population, motor vehicle related discharge (including exhaust, tires and brake wear emissions) had been becoming a major source of hazardous air pollutants in central urban areas, especially a greater contribution to toxic element concentrations in small-size aerosols. 3.3. Distribution of toxic elements in different fraction of the BCR three step sequential extraction

Fig. 5. Average enrichment factor of elements in aerosol by functional district in Beijing.

Fig. 8 illustrated the chemical species distribution of various elements in PM10 and PM2.5 at the urban downtowndBNU sampling point. In particular, the percentage of elements in mobile fraction, such as acid soluble fraction (F1) and reducible fraction (F2), was of special significant because it indicated that these elements had direct impacts on environment and the health of exposed population. The bioavailability of trace elements in PM could be calculated by the proportion of F1 to the sum of F1, F2, F3 and F4 (Qian et al., 2011). The higher the proportion, the stronger

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Fig. 6. Factor profiles for TSP (% of species total) obtained from EPA PMF 3.0 model.

the bioavailability of trace elements and the greater the adverse impacts on the environment and the health of exposed population. The concentrations in percentages of eight toxic trace elements in the respective speciation fractions could be seen graphically in Fig. 8. These eight elements could be fall into three groups. One group of elements was presented with high proportions in the exchangeable & carbonate fraction (As, Cd, Pb and Zn). When the pH value in the environment changed, these elements were subjective to release to environment and easily available to human body. The second group (Cu) exhibited higher percentages in the reducible and oxidizable fractions. The reducible fraction mainly existed in the form of iron and manganese oxides or agglomeration, and it was not easily be released to normal environment. Whilst, when the atmospheric environment in acidic condition, toxic elements in oxidizable fraction could be released with environmental

acid decreased. The third group of elements (Cr, Ni and Sb) accounted for higher percentages in the bound to residual fraction, and these elements existed in a very stable state and imposed less impact on environment and public health. Also, these eight toxic elements, which were highly mobile in PM10, exhibited even higher mobility in PM2.5 samples, indicating that these toxic elements in fine particles could more easily enter deeper into human body and lead to more serious adverse effects on human health. Furthermore, seasonal variations of mobility with toxic elements at BNU site were presented in Fig. S2. A majority of toxic elements had the highest relative abundance in mobile fraction in summer and the lowest percentage in the mobile fraction in spring, which was consistent with Schleicher's research (Schleicher et al., 2012). In particular, the mobility of As in spring showed important differences between PM10 and PM2.5. For PM10, As was

Fig. 7. Factor profiles for PM2.5 (% of species total) obtained from EPA PMF 3.0 model.

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Fig. 8. Speciation distributions of toxic elements as percentage of the elemental concentration in PM10 and PM2.5 at urban site (n ¼ 56). F1: Acid soluble (exchangeable & carbonate fractions); F2: Reducible (Fe/Mn oxyhydroxides); F3: Oxidizable (organic and sulphide fractions); F4: Residual fractions.

immobile in spring, while highly mobile in PM2.5, indicating that As in fine particles was more easily available to human body and do harm to public health. The bioavailability of toxic elements in PM2.5 at BNU site compared with that at 4th ring site was given in Fig. S3. These two sampling sites were located in the urban central areas of Beijing, which could be represented the overall pollution level of the city. It could be seen that summer was the season with higher percentage in the mobile fraction of toxic elements than winter at both sites. For Cd, Pb and Zn, the higher bioavailability appeared at 4th ring site in both seasons, while As appeared mostly in the mobile fraction at BNU site at summer. In general, some of toxic elements (As, Cd, Pb, and Zn) showed higher proportion in the mobile fractions in fine particles at central urban areas. These elements were of special concern with regard to adverse health effects. Additionally, it could be seen that these toxic trace elements were all heavy metals and metalloid. Seeing that the heavy metal pollution events occurred constantly in recent years, the Chinese government had laid more emphasis on the heavy metal pollution. Since 2010, the government tried to speed up the formulation and revision of ambient air quality standards and strengthened the emission control of heavy metal pollutants. General advices had mainly focused on strengthening monitoring of environment and emission source; designing and applying best-available control technologies for heavy metal removal. By Combining with the released guidance values of WHO and the actual situation of China, the limit of heavy metal concentrations in the ambient air quality standards in China as well as the emission limits for various anthropogenic sources should be revised and tightened in order to further reduce atmospheric environmental risk of heavy metal pollution. 4. Conclusions In this study, TSP/PM10/PM2.5 mass concentrations and its chemical speciation of totally 19 trace elements were detected at four sampling sites during four seasons in Beijing of China. Our results showed that high levels of some trace elements in fine PM, such as As, Mn, and Cd, revealing that the pollution of trace heavy metals and As in Beijing could not be neglected. EPA PMF 3.0 analysis indicated three dominant sources, and of them crust related sources, combustion sources and traffic and steel industrial related sources. In view of EFs, it could be concluded that As, Cd, Cu, Pb, S, Sb, Se and Zn were generally emitted from anthropogenic sources, while Be, Ca, Co, Fe, K, Mg, Mn and Na were mainly originated from natural emission sources. Notably, Cr and Ni were from the “mixed origin” sources.

Three groups of eight toxic trace elements could be divided by the BCR three step sequential extraction procedure. Elements of As, Cd, Pb and Zn exhibited higher mobility than the other elements, therefore, these elements were lightly to release to environment and easily available to human body. A majority of toxic elements had the lowest relative abundance in the mobile fraction in spring and the highest percentage in summer. Higher percentages of As, Cd, Pb and Zn were demonstrated in the bound to mobile fractions in fine particles at the central urban areas of Beijing. Therefore, special concerns should be paid to these toxic elements, when planning and implementing comprehensive mitigation policies in Beijing as well as its neighboring cities in Tianjin and Hebei Province. Acknowledgments This work is fund by the National Natural Science Foundation of China (40975061, 21177012, and 21377012), Open fund of State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex (SCAPC201305) and the special fund of State Key Joint Laboratory of Environmental Simulation and Pollution Control (13L02ESPC). Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.atmosenv.2014.08.081. References BJEPB (Beijing Environmental Protection Bureau) Website, 2012a. (http://www.bje pb.gov.cn/). BJEPB (Beijing Environmental Protection Bureau), 2012b. Beijing Environmental Statement 2011. Chillrud, S.N., Epstein, D., Ross, J.M., Sax, S.N., Pederson, D., Spengler, J., Kinney, P.L., 2004. Elevated airborne exposures of teenagers to manganese, chromium, and iron from steel dust and New York City's subway system. Environ. Sci. Technol. 38, 732e737. da Silva, L.I.D., de Souza Sarkis, J.E., Zotin, F.M.Z., Carneiro, M.C., Neto, A.A., da Silva, A.S.A.G., Cardoso, M.J.B., Monteiro, M.I.C., 2008. Traffic and catalytic converter-related atmospheric contamination in the metropolitan region of the city of Rio de Janeiro, Brazil. Chemosphere 71, 677e684. Duan, F.K., He, K.B., Ma, Y.L., Yang, F.M., Yu, X.C., Cadle, S.H., Chan, T., Mulawa, P.A., 2006. Concentration and chemical characteristics of PM2.5 in Beijing, China: 2001e2002. Sci. Total Environ. 355, 264e275. Duan, J.C., Tan, J.H., Hao, J.M., Chai, F.H., 2014. Size distribution, characteristics and sources of heavy metals in haze episode in Beijing. J. Environ. Sci. 26, 189e196. Duan, J.C., Tan, J.H., Wang, S.L., Hao, J.M., Chai, F.H., 2012. Size distributions and sources of elements in particulate matter at curbside, urban and rural sites in Beijing. J. Environ. Sci. 24, 87e94.

J. Gao et al. / Atmospheric Environment 99 (2014) 257e265 He, X., Li, C.C., Lau, A.K.H., Deng, Z.Z., Mao, J.T., Wang, M.H., Liu, X.Y., 2009. An intensive study of aerosol optical properties in Beijing urban area. Atmos. Chem. Phys. 9, 8903e8915. Iijima, A., Sato, K., Yano, K., Tago, H., Kato, M., Kimura, H., Furuta, N., 2007. Particle size and composition distribution analysis of automotive brake abrasion dusts for the evaluation of antimony sources of airborne particulate matter. Atmos. Environ. 41, 4908e4919. Iijima, A., Sato, K., Fujitani, Y., Fujimori, E., Saito, Y., Tanabe, K., Ohara, T., Kozawa, K., Furuta, N., 2009. Clarification of the predominant emission sources of antimony in airborne particulate matter and estimation of their effects on the atmosphere in Japan. Environ. Chem. 6, 122e132. Johansson, C., Norman, M., Burman, L., 2009. Road traffic emission factors for heavy metals. Atmos. Environ. 43, 4681e4688. Manalis, N., Grivas, G., Protonotarios, V., Moutsatsou, A., Samara, C., Chaloulakou, A., 2005. Toxic metal content of particulate matter (PM10), within the Greater Area of Athens. Chemosphere 60, 557e566. Mason, B., Moore, C.B., 1982. Principles of Geochemistry, fourth ed. Wiley, New York. MEP (Ministry of Environmental Protection of the People’s Republic of China), 2012. Ambient Air Quality Standard (GB 3095-2012). http://kjs.mep.gov.cn/hjbhbz/ bzwb/dqhjbh/dqhjzlbz/201203/W020120410330232398521.pdf (retrieved September 2013, in Chinese). National Bureau of Statistics (NBS), 2011a. China Statistical Yearbook 2011. P.R. China. China Statistics Press, Beijing, China. National Bureau of Statistics (NBS), 2011b. China Energy Statistical Yearbook 2011. P.R. China. China Statistics Press, Beijing, China. Okuda, T., Kato, J., Mori, J., Tenmoku, M., Suda, Y., Tanaka, S., He, K., Ma, Y., Yang, F., Yu, X., Duan, F., Lei, Y., 2004. Daily concentrations of trace metals in aerosols in Beijing, China, determined by using inductively coupled plasma mass spectrometry equipped with laser ablation analysis, and source identification of aerosols. Sci. Total Environ. 330, 145e158. Okuda, T., Katsuno, M., Naoi, D., Nakao, S., Tanaka, S., He, K.B., Ma, Y.L., Lei, Y., Jia, Y.T., 2008. Trends in hazardous trace metal concentrations in aerosols collected in Beijing, China from 2001 to 2006. Chemosphere 72, 917e924. Paatero, P., 2004. User's Guide for Positive Matrix Factorization Programs PMF2 and PMF3, Part 1: Tutorial. Polissar, A.V., Hopke, P.K., Paatero, P., Malm, W.C., Sisler, J.F., 1998. Atmospheric aerosol over Alaska 2. Elemental composition and sources. J. Geophys. Res. 103, 19045e19057. Qian, F., Yang, Y.F., Zhang, H.F., 2011. Distribution characteristics and speciation of heavy metals in PM10 near urban roads and surrounding areas of Beijing. Res. Environ. Sci. 6, 608e614 (in Chinese). Quevauviller, P., Rauret, G., Griepink, B., 1993. Single and sequential extraction in sediments and soils. Int. J. Environ. Anal. Chem. 51, 231e235. ~ o, P., Ahumada, I., Giordano, A., 2007. Total element concentration Richter, P., Grin and chemical fractionation in airborne particulate matter from Santiago, Chile. Atmos. Environ. 41, 6729e6738. Schleicher, N., Norra, S., Chai, F.H., Chen, Y.Z., Wang, S.L., Cen, K., Yu, Y., Stüben, D., 2012. Mobility of trace metals in urban atmospheric particulates matter of Beijing, China. Urban Environment. In: Proceedings of the 10th Urban Environment Symposium. Alliance for Global Sustainability Bookseries, vol. 19, pp. 191e200. Song, S.J., Wu, Y., Jiang, J.K., Yang, L., Cheng, Y., Hao, J.M., 2012. Chemical characteristics of size-resolved PM2.5 at a roadside environment in Beijing, China. Environ. Pollut. 161, 215e221. Song, Y., Zhuang, G.S., Xie, S.D., Zeng, L.M., Zheng, M., Salmon, L.G., Shao, M., Slanina, S., 2006. Source apportionment of PM2.5 in Beijing by positive matrix factorization. Atmos. Environ. 40, 1526e1537.

265

€din, A., Andre asson, K., 2002. Metal emissions from road traffic and Sternbeck, J., Sjo the influence of resuspension-results from two tunnel studies. Atmos. Environ. 36, 4735e4744. Streets, D.G., Fu, J.S., Jang, C.J., Hao, J.M., He, K.B., Tang, X.Y., Zhang, Y.H., Wang, Z.F., Li, Z.P., Zhang, Q., Wang, L.T., Wang, B.Y., Yu, C., 2007. Air quality during the 2008 Beijing Olympic Games. Atmos. Environ. 41, 480e492. Sun, Y.L., Zhuang, G.S., Wang, Y., Han, L.H., Guo, J.H., Dan, M., Zhang, W.J., Wang, Z.F., Hao, Z.P., 2004. The air-borne particulate pollution in Beijing e concentration, composition, distribution and sources. Atmos. Environ. 38, 5991e6004. Tian, H.Z., Cheng, K., Wang, Y., Zhao, D., Lu, L., Jia, W.X., Hao, J.M., 2012a. Temporal and spatial variation characteristics of atmospheric emissions of Cd, Cr, and Pb from coal in China. Atmos. Environ. 50, 157e163. Tian, H.Z., Gao, J.J., Long, L., Zhao, D., Cheng, K., Qiu, P.P., 2012b. Temporal trends and spatial variation characteristics of hazardous air pollutant emission inventory from municipal solid waste incineration in China. Environ. Sci. Technol. 46, 10364e10371. Tian, H.Z., Lu, L., Cheng, K., Hao, J.M., Zhao, D., Wang, Y., Jia, W.X., Qiu, P.P., 2012c. Anthropogenic atmospheric nickel emissions and its distribution characteristics in China. Sci. Total Environ. 417e418, 148e157. Tian, H.Z., Wang, Y., Xue, Z.G., Cheng, K., Qu, Y.P., Chai, F.H., Hao, J.M., 2010. Trend and characteristics of atmospheric emissions of Hg, As, and Se from coal combustion in China, 1980e2007. Atmos. Chem. Phys. 10, 11905e11919. Tian, H.Z., Wang, Y., Xue, Z.G., Qu, Y.P., Chai, F.H., Hao, J.M., 2011. Atmospheric emissions estimation of Hg, As, and Se from coal-fired power plants in China, 2007. Sci. Total Environ. 409, 3078e3081. Tian, H.Z., Zhao, D., Cheng, K., Lu, L., He, M.C., Hao, J.M., 2012d. Anthropogenic atmospheric emissions of antimony and its spatial distribution characteristics in China. Environ. Sci. Technol. 46, 3973e3980. Trapp, J.M., Millero, F.J., Prospero, J.M., 2010. Temporal variability of the elemental composition of African dust measured in trade wind aerosols at Barbados and Miami. Mar. Chem. 120, 71e82. Valavanidis, A., Fiotakis, K., Vlahogianni, T., Bakeas, E.B., Triantafillaki, S., Paraskevopoulou, V., Dassenakis, M., 2006. Characterization of atmospheric particulates, particle-bound transition metals and polycyclic aromatic hydrocarbons of urban air in the centre of Athens (Greece). Chemosphere 65, 760e768. Wang, X.Y., Dong, F.M., Jin, M.H., Pan, X.C., 2013. The impact of ambient particular matter (PM10) on the population mortality for cerebrovascular diseases-a casecrossover study. Zhonghua Liuxingbingxue Zazhi 34, 331e335 (in Chinese). Wang, Z.J., 2002. Epidemiology of lung cancer. Chin. J. Cancer Prev. Treat. 9, 1e5 (in Chinese). WHO, 2000. Guidelines for Air Quality Geneva. World Health Organization. WHO, 2001. Environment and People's Health in China. Zhang, R., Jing, J., Tao, J., Hsu, S.C., Wang, G., Cao, J., Lee, C.S.L., Zhu, L., Chen, Z., Zhao, Y., Shen, Z., 2013. Chemical characterization and source apportionment of PM2.5 in Beijing: seasonal perspective. Atmos. Chem. Phys. 13, 7053e7074. Zhao, Q., He, K.B., Ma, Y.L., Jia, Y.T., Cheng, Y., Liu, H., Wang, S.W., 2009. Regional PM pollution in Beijing and surrounding area during summertime. Environ. Sci. 30, 1873e1880 (in Chinese). Zhou, J.M., Zhang, R.J., Cao, J.J., Chow, J.C., Watson, J.G., 2012. Carbonaceous and ionic components of atmospheric fine particles in Beijing and their impact on atmospheric visibility. Aerosol Air Qual. Res. 12, 492e502. Zhu, X.L., Zhang, Y.H., Zeng, L.M., Wang, W., 2005. Source identification of ambient PM2.5 in Beijing. Res. Environ. Sci. 18, 1e5 (in Chinese).