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Atmospheric Environment 45 (2011) 6210e6215

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Atmospheric Environment

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Trace elements and lead isotopic composition of PM10 in Lhasa, Tibet

Zhiyuan Cong a,b, Shichang Kang a,c,*, Chunling Luo b,d, Qing Li a, Jie Huang a,Shaopeng Gao a, Xiangdong Li b

aKey Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, ChinabDepartment of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kongc State Key Laboratory of Cryospheric Sciences, Chinese Academy of Sciences, Lanzhou 730000, ChinadGuangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China

a r t i c l e i n f o

Article history:Received 1 March 2011Received in revised form18 July 2011Accepted 29 July 2011

Keywords:Atmospheric aerosolsTrace elementsPb isotopeLhasaTibetan Plateau

* Corresponding author. Present address: InstituteChinese Academy of Sciences, 18 Shuangqing Road, HaChina. Tel./fax: þ86 10 62849681.

E-mail address: shichang.kang@itpcas.ac.cn (S. Ka

1352-2310/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.atmosenv.2011.07.060

a b s t r a c t

This paper presents the first detailed investigation on airborne trace metals and their potential majorsources at Lhasa, the largest city in Tibetan Plateau (TP). The whole year PM10 samples were collectedduring September 2007 and August 2008. The annual average concentration of PM10 in Lhasa was51.8� 42.5 mgm�3, lower than those of major Asian cities. Distinct seasonal patterns were observed inPM10 concentration, with higher concentrations in winter, and lower in summer. The mean elementalconcentrations were generally comparable with other urban areas, but significantly higher than thosefrom a remote site in TP (i.e., Nam Co). Crustal elements, including Na, Mg, Al, K, Ca, Sc, Ti, V, Mn, Fe, Asand Ba, had similar seasonal patterns in PM10, while other elements, such as Cr, Co, Ni, Cu, Zn, and Cd,had less distinct seasonal variations, suggesting more anthropogenic inputs of the latter group. The resultof principle component analysis (PCA) on trace elements demonstrated that fugitive dusts, trafficemissions and waste incineration activities were probably the major sources of anthropogenic metals inthe atmosphere at Lhasa. The Pb isotopic compositions revealed that the metal was mainly originatedfrom nature background with a minor contribution from the cement factory. The data obtained in thisstudy can be useful for making pollution control strategies in the city, and also valuable for trace elementstudies in other environmental medium, such as snow, ice core, and lake sediments in the TP region.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

The role of aerosols (particulate matters) in the global climatechange has long been recognized (IPCC, 2007). Moreover, aerosolscan adversely affect the human health via inhalation, especially inthe urban environment (Poschl, 2005). Trace elements are impor-tant components of aerosols. Industrial, residential, and traffic-related activities have resulted in a substantial increase of tracemetals (e.g., Cu, Pb, Zn, Cd, Ni etc.) in the atmosphere (Nriagu andPacyna, 1988; Yatkin and Bayram, 2008). A detailed knowledge onthe characteristics of trace metals in aerosols is fundamental forassessing the air quality and providing possible measures forenvironmental management (Ayrault et al., 2010; Khan et al., 2010).

The Tibetan Plateau (TP) has an immense land area (about2,500,000 km2) with the mean elevation of more than 4000 m

of Tibetan Plateau Research,idian District, Beijing 100085,

ng).

All rights reserved.

above sea level (a.s.l.). The atmosphere over the plateau is probablythe least affected by human activities in the Asian continent due tothe geographical conditions, the sparse population, and minimalindustrial activities. Therefore, it is generally regarded as a remoteand pristine region, representing a large scale regional backgroundcondition. Recently, several researches have revealed the long-range transport of pollutants to TP (e.g., POPs and heavy metals)from South and Central Asia carried by the atmospheric circulation(Cheng et al., 2007; Cong et al., 2007; Loewen et al., 2007;Wu et al.,2009; Wang et al., 2010). At the same time, some researchers alsopointed out the local contribution of those contaminants shouldnot be neglected (Li et al., 2008; Yang et al., 2010). Therefore, moreresearch work, especially inside the TP, is needed to quantitativelydifferentiate the contribution of local and long-range transportedair pollutants.

Lhasa, the metropolis of the Tibet Autonomous Region of China, islocated around 3650m a.s.l, with a population of about 300,000. Thecity has limited industrial facilities, and the fossil fuel consumption isrelatively low. In recent years, with the rapid development of localeconomy, Lhasa is experiencing dramatic urbanization process withincreasing motor vehicles and inflowing tourists. The growing energy

Z. Cong et al. / Atmospheric Environment 45 (2011) 6210e6215 6211

consumptionmay affect the atmospheric environment in the city. Theunique location, the structure of energy consumption, and the religionactivities make Lhasa a special atmospheric environment, which ismuch different from other cities in the world, and is becominga subject of scientific interest and public concerns (Zhang et al., 2001;Huang et al., 2010).

The objective of the present research was to characterize theelemental composition and Pb isotope signatures in the urbanatmosphere of Lhasa in order to understand the origin of thoseconstituents, and to evaluate the impacts of increasing anthropo-genic activities on the atmosphere.

2. Methodology

2.1. Site description and sampling

The sampling was conducted on the rooftop of the tallestbuilding at the Institute of Tibetan Plateau Research, Lhasa branch(20 m above ground level), which is located at Jinzhu West Road,western part of Lhasa city (Fig.1). This site is considered as an urbanlocation where air quality is mainly influenced by emissionsfrom vehicular traffic, residential and religionary activities. PM10(particulatematters with a diameter less than 10 mm) samples werecollected using an Airmetrics Minivol sampler with PM10 impactorinlets at a flow rate of 5 Lmin�1. The air volume was converted intostandard condition according to the ambient conditions in Lhasa.Totally 59 samples (Zefluor PTFE membranes, 47 mm, Pall LifeSciences, USA) of 24-h duration were collected at every sixth dayfrom September 2007 to August 2008.

Filters were equilibrated in a silica gel desiccator for 24 h beforeand after sampling. The PM10 masses on the filers were determinedgravimetrically using an electronic microbalance with 10 mgsensitivity (AUW220D, Shimadzu). The meteorological parametersduring the sampling period are summarized in Table 1.

2.2. Analytical methodology

The collected PTFE filters were initially placed in a Teflon high-pressure digestion vessel with 1.5 mL concentrated HNO3 and0.5 mL concentrated HF. Subsequently, the vessels were treated inultrasonic bath for 20 min. The samples were then digested in anoven at 190 �C for 4 h. After cooling, the solutions were heated ona hot plate at 150 �C, and 0.5 mL HNO3 was added into the residue,

Fig. 1. The location map of the sampling

and further heated at 170 �C for 4 h. This digestion procedure wasrepeated twice. Finally, Indium and Rhodium (100 ng) were addedas internal standards, and the digest was diluted up to 10 mL usingMilli-Q� water. In each digestion batch (20 samples), a reagentblank was also used to check the sample handing processes.

A total of 19 elements (Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co,Ni, Cu, Zn, As, Cd, Ba and Pb) were measured by InductivelyCoupled Plasma-Mass Spectrometry (ICP-MS, X-7 ThermoElemental) at the Institute of Tibetan Plateau Research, Beijingbranch. Elemental concentrations were quantified using externalcalibration standards (AccuTrace� Reference Standard). A checkstandard was analyzed after the initial calibration and after every10 samples. The method detection limits (MDLs), defined as threetimes the standard deviation of replicate blanks measurements,were Na, 0.26 mg L�1; Mg, 0.066 mg L�1; Al, 0.14 mg L�1; K,0.063 mg L�1; Ca, 0.81 mg L�1; Sc, 0.003 mg L�1; Ti, 0.26 mg L�1; V,0.039 mg L�1; Cr, 0.048 mg L�1; Mn, 0.018 mg L�1; Fe, 0.51 mg L�1; Co,0.015 mg L�1; Ni, 0.066 mg L�1; Cu, 0.036 mg L�1; Zn, 0.20 mg L�1; As,0.001 mg L�1; Cd, 0.002 mg L�1; Ba, 0.024 mg L�1; and Pb,0.021 mg L�1. The accuracy and precision of the analytical protocolwere evaluated by the analysis of 1 mg Chinese Loess ReferenceMaterial (GBW07408) with a blank filter using the same digestionmethod. It was found that the recoveries ranged from 87% for Cd to110% for Ti. For precision, the corresponding RSD values of allelement concentrations measured in the reference material wereless than 5%. The final concentrations were corrected with reagentand filter blanks. All of the concentrations of trace metals found inthe field blanks were <10% of those found in the PM10 samplesfrom Lhasa.

The Pb isotopic composition analysis was conducted using ICP-MS (Perkin Elmer Scix Elan 6100 DRCplus) at The Hong KongPolytechnic University. Only those solutions with Pb concentra-tion above 20 mg L�1 were analyzed considering the performanceof the instrument. The analytical parameters were set as 250sweeps per reading, and 10 readings per samples solution.Procedural blanks and standard reference material (NIST SRM981, common lead) were used for quality control. The certifiedvalues of 204Pb/207Pb, 206Pb/207Pb, and 208Pb/207Pb were 0.06455,1.0933, and 2.3704, respectively. The analysis was repeated whenthe differences between the measured and certified values of thestandard reference materials exceeded 0.5%. The precision (%RSD) of the Pb isotopic ratios of the 10 replicates was typically<0.5%.

site in Lhasa city, Tibetan Plateau.

Table 1Monthly average meteorological parameters at Lhasa during sampling period.

Sep. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May Jun. Jul. Aug.

Temp. (�C) 15 13 5 3 2 2 6 10 14 16 16 16Precipitation (mm) 48 1 2 0 0 7 2 2 65 59 130 128Wind speed (kmh�1) 5 5 5 5 7 7 7 6 7 6 5 5Dew point (�C) 4 �5 �16 �21 �23 �21 �12 �9 0 4 6 7

Z. Cong et al. / Atmospheric Environment 45 (2011) 6210e62156212

3. Results and discussion

3.1. PM10 concentrations

The concentrations of PM10 in Lhasa ranged from 6.94to 160 mgm�3 with the annual mean concentration of51.8� 42.5 mgm�3. In general, only 3% sampling days in our studyexceeded the U. S. National Ambient Air Quality Standard (NAAQS)(150 mgm�3) for a 24 h period, and China’s Ambient Air QualityStandard (CAAQS) for cities (limit of 150 mgm�3 as “light pollu-tion”). The PM10 concentrations indicated that Lhasa had a rela-tively low particulate matter loading compared with other Asiancities, such as Beijing (172 mgm�3), Wuhan (156e197 mgm�3),Lahore, Pakistan (340 mgm�3) and Agra, India (154 mgm�3), whilethe situation was similar to some European cities, such as Bern,Switzerland (40 mgm�3), and Budapest, Hungary (48e54 mgm�3)(Table 2).

We also calculated the PM10 concentrations based on the AirPollution Index (API) reported by the Ministry of EnvironmentalProtection of China using the methods described in literature (Sunet al., 2005). As the results, the PM10 concentration and variationsobserved at our sampling sitewere quite similar to the reported APIPM10 values in Lhasa (y¼ 1.02xþ 6.27, R2: 0.85), indicating oursampling site is a good representative site of the situation of theentire city.

Table 2Statistical summary of trace elements in PM10 samples of Lhasa city and reported data in

This study Nam Coa Wuhanb B

Mean (S.D.) Range

PM10 (mgm�3) 51.8 (42.5) 6.9e160 e 156 17Na 345 (210) 52e987 e 1000 16Mg 269 (188) 45e1020 12 1000 20Al 1450 (1200) 121e7290 131 e 53K 614 (462) 77e2550 82 4000 e

Ca 1640 (851) 317e4060 251 5000 90Sc 0.27 (0.24) 0.03e1.5 e 1 e

Ti 108 (87) 19e467 10 214 33V 4.8 (2.9) 0.97e15 0.06 7 e

Cr 19 (24) 1.5e152 1 11 40Mn 27 (21) 4.4e104 3.7 116 11Fe 1034 (762) 145e4380 94 3000 37Co 1.8 (1.7) 0.33e12 e 1 e

Ni 7.2 (9.3) 0.55e59 0.95 4 40Cu 9.1 (8.8) 2.3e61 0.56 40 50Zn 81 (96) 14e541 1.8 676 33As 1.8 (1.2) 0.32e6.6 0.04 66 20Cd 0.52 (0.52) 0.06e3.4 e 10 2.Ba 12 (8.6) 1.7e44 e 58 e

Pb 37 (29) 3.4e124 e 409 11

“e” Means not available/analyzed.a TSP, Nam Co, central Tibetan Plateau, summer 2005 (Cong et al., 2007).b PM10, Hankou, Wuhan, China, September 2003eSeptember 2004 (Querol et al., 2006c PM10, Beijing Normal University, China, summer 2002e2003 (Sun et al., 2004).d PM10, Agra, India, May 2006eMarch 2008 (Kulshrestha et al., 2009).e PM10, Lahore, Pakistan, 2007 (von Schneidemesser et al., 2010).f PM10, Kendlerstraße, Vienna, Austria, 2004 (Limbeck et al., 2009).g PM10, Bern, Switzerland, April 1998eMarch 1999 (Hueglin et al., 2005).h PM10, Budapest, Hungary, spring 2002 (Maenhaut et al., 2005).

3.2. Elemental composition

Table 2 shows the annual mean and range of elementalconcentrations (ngm�3) during the sampling period. According tothe statistical summary in Table 2, the concentration of Sc wasfound to be the lowest with a value of 0.27 ngm�3, while Cashowed the highest concentration at 1640 ngm�3. Based on theconcentrations, the elements analyzed can be grouped into fourcategories: (1) <1 ngm�3: Sc and Cd; (2) <10 ngm�3: V, Co, Ni, Cu,and As; (3) <100 ngm�3: Cr, Mn, Zn, Ba, and Pb; (4) >100 ngm�3:Na, Mg, Al, K, Ca, Ti, Fe. Overall, the measured trace elementsconstituted about 12% of the mass of PM10 in Lhasa excluding theirchemical compounds. The seven major elements (Na, Mg, Al, K, Ca,Ti and Fe) account for about 96% of the total metal concentrations inthe air mass.

In comparisonwithNamCo, a remote site (N30�46.440, E90�59.310,4730 m a.s.l.) representing the regional background condition in TP(Cong et al., 2007), the averaged concentrations of elements in Lhasawere significantly higher, from 6.5 fold for Ca to 80 fold for V, indi-cating the obvious influences of anthropogenic activities on theatmospheric environment in the city.

The annual mean threshold concentrations of trace elements inPM10 set by the European Union are 6 ngm�3, 5 ngm�3, and20 ngm�3 for As, Cd, and Ni, respectively (European-Commission,2005; Manalis et al., 2005). According to the air concentration

other cities (ngm�3).

eijingc Agra,Indiad

Lahore,Pakistane

Vienna,Austriaf

Bern,Switzerlandg

Budapest,Hungaryh

2 154 340 27.7 40.2 48e5400 e 1900 e 665 45040 e 2100 260 85 48030 e 8400 520 152 1060

e 5600 e 255 42050 e 9100 1310 1199 2600

e e e e 0.180 e 560 15 e 73

e 21 1.4 1.4 2.9300 30 5.5 e 8.9

0 900 300 13 25 3030 2900 8200 780 2048 1930

e 3.1 1.8 e 0.48200 18 5.7 3 3.240 73 21 74 61

0 500 11,000 40 e 84e 22 0.9 0.8 1.4

43 e 77 0.5 0.26 e

e 120 12 e 520 1100 4400 11 49 24

).

Z. Cong et al. / Atmospheric Environment 45 (2011) 6210e6215 6213

guidelines established by the World Health Organization, theannual threshold concentration for Pb is 500 ngm�3, and150 ngm�3 for Mn in PM10 (WHO, 2000). The concentrations forthose trace metals in Lhasa were all lower than the recommendedconcentrations mentioned above.

To further compare the element concentrations in PM, data fromother cities have also been included in Table 2. The concentrationsof trace elements in Lhasa were generally comparable with Euro-pean urban sites, such as Vienna, Bern and Budapest. However, incomparison with some Asian cities, such as Beijing, Chinaand Lahore, Pakistan, the concentrations of the trace elementsmeasured in Lhasa were much lower. For example, the Pbconcentration in Agra and Lahore were 30 and 119 times higherthan that in Lhasa.

3.3. Seasonal variations

Changes in the meteorological conditions as well as the sourceemission strength may change atmospheric components with time.Fig. 2a shows themonthly average PM10 concentrations observed inLhasa during the study period. The higher PM10 concentrationsoccurred in winter, and lower concentrations were recorded insummer. The PM mass levels appeared to be correlated negativelywith the precipitation. During the winter period, the precipitationwas minimal (Table 1), and dust suspension increased the PMmassconcentrations. At the same time, the low temperature in wintermay also result in low inversion layer with more particulate mattertrapped near the ground level (Dronga et al., 2008). In addition,

Fig. 2. Monthly average values for PM10, Al and Ni concentrations in Lhasa from Sep.2007 to Aug. 2008. Al represents the element group that exhibit similar seasonalconcentration variation to PM mass. Ni represents the element group without clearvariation pattern.

enhanced combustion activities of local residents for domesticheating could also contribute to the increased concentrations of PMin the city. The low concentrations of PM in summer were likelyrelated to the decreased soil suspension due to the flourishingvegetation cover, the washout of air particles by more precipitation(Table 1), and higher mixing height facilitating the PM dilution anddispersion. Based on the daily data, the PM10 also exhibiteda positive relation with the wind speed, which was in agreementwith the previous research by Dronga et al. (2008).

In general, elements measured in the PM10 samples of Lhasa dis-played clear seasonal variation patterns: The first group elements,including Na, Mg, Al, K, Ca, Sc, Ti, V, Mn, Fe, As and Ba, exhibitedpronounced difference among different seasons with the order forthese elements of winter> spring> autumn> summer (Fig. 2b),which were generally in agreement with the PM10 seasonal variationtrends (Fig. 2a). While the remaining elements, such as Cr, Co, Ni, Cu,Zn, and Cd, did not show a clear seasonal pattern (Fig. 2c), whichmaysuggest they were more related to anthropogenic activities, such astraffic emissions which did not change greatly throughout the year.

3.4. Sources of elements e principal component analysis

Principal component analysis (PCA) is a multivariate statisticalmethod and frequently used to simplify large and complex datasets, and then identify correlated variables (possible commonsources). In this study, Varimax rotated PCA was performed usingSPSS 13.0 software (see results in Table 3). Three major componentswere identified with eigen values greater than 1, and explaineda sum of 80.2% of the overall variances in the data set.

The first component had high loadings for Na, Mg, Al, K, Ca, Sc,Ti, V, Mn, Fe, As, Ba and Pb, most of which are typical major andtrace elements from the fugitive dust of natural origins. Fugitivedust sources include naturally windblown dust, agricultural tilling,construction dust, and road dust. This component accounted for46.7% of the total variance in the data set. These elements wereclosely associated with the PM10 mass values, indicating theirsubstantial contribution to the mass of particulate matter. Inter-estingly, Pb had high loading (0.60) in Component 1 although it isgeneral recognized as a typical anthropogenic element in urban

Table 3Varimax rotated factor loading matrix for elements in PM10 from Lhasa.

Components

1 2 3

PM10 0.783 0.184 �0.008Na 0.746 0.436 0.206Mg 0.964 0.098 0.137Al 0.976 0.085 0.071K 0.907 0.260 0.019Ca 0.834 0.143 0.259Sc 0.967 0.021 0.024Ti 0.876 �0.069 0.298V 0.606 �0.052 0.489Cr �0.007 0.161 0.903Mn 0.852 0.296 0.290Fe 0.935 0.192 0.218Co 0.344 �0.264 0.570Ni 0.013 0.878 �0.029Cu 0.347 0.612 0.271Zn 0.082 0.868 �0.016As 0.665 0.441 0.431Cd 0.058 0.154 0.930Ba 0.928 0.196 0.094Pb 0.600 0.590 0.044

% Variance 46.7 18.7 14.8

Z. Cong et al. / Atmospheric Environment 45 (2011) 6210e62156214

areas. More detailed discussion about the source of Pb in LhasaPM10 samples is provided in the next section.

Component 2 was characterized by Cu, Zn and Ni, accounting for18.7% of the total variance. This group of elements may representthe combined sources of traffic emissions and other anthropogenicactivities. Exhaust emissions from vehicles could contain variousamounts of Cu, Zn and Ni (Pakkanen et al., 2003). Cu in urbanaerosols also arises from brakewear of vehicles (Weckwerth, 2001).Zn may be also derived from various industrial sources, and theabrasion of rubber tires on roads (Rogge et al., 1993). Ni is regardedas an indicator of emissions from fuel burning and vehicularemissions (Pacyna and Pacyna, 2001). As a typical tourist city, thereare no major industrial facilities around Lhasa, except a cementfactory in west suburban with annual production capacity of200,000 tons (Lhasa Bureau of Statistics, 2010).

Component 3 explained 14.8% of the total variance, and wasmainly associated with the elements of Cr, Co and Cd, which couldbe attributed to the solid waste incineration (Pacyna and Pacyna,2001). Cr and Cd are important pollutants from solid waste treat-ment (Kulshrestha et al., 2009). In suburban area of Lhasa, due tothe limited access to municipal solid waste treatment, many refusedumps were burned casually by the local residents (Jiang et al.,2009), which could be one of major sources of atmospheric pollu-tion, and should be considered in future environment managementprogram.

3.5. Lead isotopic compositions of PM10

Besides the natural background, the major sources of anthro-pogenic Pb in the atmosphere include the combustion of leadedgasoline by automobile, industrial discharges and coal burning(Mukai et al., 2001; Widory et al., 2010). Different Pb sourcesusually exhibit their own characteristic Pb isotope ratios. At thesame time, the isotope compositions are generally not affected byphysical and/or chemical fractionation processes in the environ-ment. Therefore, the isotopic compositions of Pb are employed asa reliable tool for source apportionment and source regions iden-tification (Duzgoren-Aydin et al., 2004; Lee et al., 2007).

As shown in Fig. 3, the Pb isotope signatures of most PM10 samplesfrom Lhasa fall within the scope of local soils and Chinese loess.

Fig. 3. Stable lead isotopic composition in PM10 and soil samples from Lhasa. Alsoshown are Pb isotopic ratios of emissions from Chinese coal-fired power station, Pb orerefining factories, cement factories and Chinese loess (Widory et al., 2010), as well asthe vehicle exhaust before the phase-out of leaded gasoline (Zheng et al., 2004; Zhuet al., 2010).

Therefore, the predominant Pb source in the atmosphere was prob-ably from natural background. Only one sample had similar Pbisotopic characteristic to Chinese cement factories (Widory et al.,2010). The lead content of this sample is 1050 mg g�1, and theaverage lead content of all samples analyzed is 1014� 803 mg g�1,comparable to the result of PM2.5 in Beijing (i.e. 1364 ppm) (Widoryet al., 2010). The Lhasa Dongga Cement Factory is located at the westsuburban about 10 km far away from the city center. It has an annualproduction capacity of 200,000 tons (Lhasa Bureau of Statistics, 2010).Our results demonstrated that this cement factory could contribute toanthropogenic Pb inputs in the PM10 of Lhasa city. Fig. 3 also showsthat there is no sample has similar Pb isotope ratios to leaded vehicleemissions. In China, leaded gasoline was gradually phased out from2000. The Pb isotopic characteristics of Lhasa PM10 samples indicatedthat leaded gasoline now has little influence on the atmosphereenvironment, reflecting the effectiveness of such action.

Mukai et al. (2001) suggested that coal combustion considerablycontributed to atmospheric lead in Chinese cities. However, thecurrent power demands in Lhasa rely on renewable energy forms,such as solar (4.99% of the total energy consumption), biotic (37.4%)geothermal (5.39) and water energy (28.67%), and very limited coal(5.31%) is used in Lhasa (Hua, 2009). Therefore, the influence of coalburning was not considered as a major source in the city.

4. Conclusions

The elemental composition of PM10 aerosols collected in Lhasafrom September 2007 to August 2008 was characterized in thepresent study. The PM10 concentrations indicated Lhasa hada relative low particulate matter loading with the annual averagePM10 concentration of 51.8� 42.5 mgm�3. The mean elementalconcentrations were generally comparable with other Europeanurban areas while much lower than some Asian cities. The PM10,accompanied with most crustal elements, had a pronouncedseasonal patternwith high concentrations inwinter and spring. Thepossible sources of elements in aerosols were investigated byprincipal component analysis and Pb isotopic compositions. Theresults showed that fugitive dust, traffic emission and wasteincineration were probably major contributors of anthropogenicmetals in the atmosphere at Lhasa. Pb isotope signature showedthat natural dust was the dominant source of this metal in theatmosphere, while the cement factory in suburban had a minorinfluence. The current study at Lhasa city can provide a reliabledatabase of metal contaminants from local urban sources, and willbe of use on the interpretation of trace elemental records in ice coreand lake sediment from the TP region.

Acknowledgments

This study is supportedbyNationalNatural Science FoundationofChina (40830743, 41075089), the Global Change Research Programof China (2010CB951401) and the Research Grants Council (RGC) ofthe Hong Kong SAR Government (N_PolyU535/05). The authorsgratefully appreciate the two anonymous reviewers for their helpfuland constructive comments. Special thanks to Dr. David Widory forkindly providing the Pb isotope ratios of various emission sources.

References

Ayrault, S., Senhou, A., Moskura, M., Gaudry, A., 2010. Atmospheric trace elementconcentrations in total suspended particles near Paris, France. AtmosphericEnvironment 44, 3700e3707.

Cheng, H., Zhang, G., Jiang, J.X., Li, X., Liu, X., Li, J., Zhao, Y., 2007. Organochlorinepesticides, polybrominated biphenyl ethers and lead isotopes during the springtime at the Waliguan Baseline Observatory, northwest China: implication forlong-range atmospheric transport. Atmospheric Environment 41, 4734e4747.

Z. Cong et al. / Atmospheric Environment 45 (2011) 6210e6215 6215

Cong, Z.Y., Kang, S.C., Liu, X.D., Wang, G.F., 2007. Elemental composition of aerosol inthe Nam Co region, Tibetan plateau, during summer monsoon season. Atmo-spheric Environment 41, 1180e1187.

Dronga, D., Tsering, N., Penduo, M., 2008. Correlative analysis on relationshipbetween changes of several main contaminations and some meterologicalelements in Lhasa urban area. Journal of Tibet University 23, 7e11.

Duzgoren-Aydin, N.S., Li, X.D., Wong, S.C., 2004. Lead contamination and isotopesignatures in the urban environment of Hong Kong. Environment International30, 209e217.

European-Commission, 2005. Directive 2004/107/EC of the European parliamentand of the council of 15 December 2004 relating to arsenic, cadmium, nickeland polycyclic aromatic hydrocarbons in ambient air. Official Journal of theEuropean Union L23, 3e16.

Hua, H., 2009. The energy consumption in Lhasa region. Energy Research & Utili-zation 1, 30e33.

Huang, J., Kang, S., Shen, C., Cong, Z., Liu, K., Wang, W., Liu, L., 2010. Seasonalvariations and sources of ambient fossil and biogenic-derived carbonaceousaerosols based on 14C measurements in Lhasa, Tibet. Atmospheric Research 96,553e559.

Hueglin, C., Gehrig, R., Baltensperger, U., Gysel, M., Monn, C., Vonmont, H., 2005.Chemical characterisation of PM2.5, PM10 and coarse particles at urban, near-city and rural sites in Switzerland. Atmospheric Environment 39, 637e651.

IPCC, 2007. Climate change 2007: the scientific basis. In: Solomon, S., Ding, Y.,Griggs, D.J., Noguer, M., Van der Linden, P.J., Dai, X., Maskell, K., Johnson, C.A.(Eds.), Contribution of Working Group I to the Fourth Assessment Report of theIntergovernmental Panel on Climate Change. Cambridge Univerisity Press,Cambridge.

Jiang, J., Lou, Z., Ng, S., Luobu, C., Ji, D., 2009. The current municipal solid wastemanagement situation in Tibet. Waste Management 29, 1186e1191.

Khan, M.F., Hirano, K., Masunaga, S., 2010. Quantifying the sources of hazardouselements of suspended particulate matter aerosol collected in Yokohama, Japan.Atmospheric Environment 44, 2646e2657.

Kulshrestha, A., Satsangi, P.G., Masih, J., Taneja, A., 2009. Metal concentration ofPM2.5 and PM10 particles and seasonal variations in urban and rural envi-ronment of Agra, India. Science of The Total Environment 407, 6196e6204.

Lee, C.S.L., Li, X.D., Zhang, G., Li, J., Ding, A.J., Wang, T., 2007. Heavy metals and Pbisotopic composition of aerosols in urban and suburban areas of Hong Kong andGuangzhou, South China e evidence of the long-range transport of aircontaminants. Atmospheric Environment 41, 432e447.

Lhasa Bureau of Statistics, 2010. Statistic Communique of Lhasa National Economyand Social Development in 2009 Lhasa.

Li, J., Lin, T., Qi, S., Zhang, G., Liu, X., Li, K., 2008. Evidence of local emission oforganochlorine pesticides in the Tibetan plateau. Atmospheric Environment 42,7397e7404.

Limbeck, A., Handler, M., Puls, C., Zbiral, J., Bauer, H., Puxbaum, H., 2009. Impact ofmineral components and selected trace metals on ambient PM10 concentra-tions. Atmospheric Environment 43, 530e538.

Loewen, M., Kang, S., Armstrong, D., Zhang, Q., Tomy, G., Wang, F., 2007. Atmo-spheric transport of mercury to the Tibetan plateau. Environmental Science &Technology 41, 7632e7638.

Maenhaut, W., Raes, N., Chi, X.G., Cafmeyer, J., Wang, W., Salma, I., 2005. Chemicalcomposition and mass closure for fine and coarse aerosols at a kerbside inBudapest, Hungary, in spring 2002. X-Ray Spectrometry 34, 290e296.

Manalis, N., Grivas, G., Protonotarios, V., Moutsatsou, A., Samara, C., Chaloulakou, A.,2005. Toxic metal content of particulate matter (PM10), within the Greater Areaof Athens. Chemosphere 60, 557e566.

Mukai, H., Tanaka, A., Fujii, T., Zeng, Y., Hong, Y., Tang, J., Guo, S., Xue, H., Sun, Z.,Zhou, J., Xue, D., Zhao, J., Zhai, G., Gu, J., Zhai, P., 2001. Regional characteristics of

sulfur and lead isotope ratios in the atmosphere at several Chinese urban sites.Environmental Science & Technology 35, 1064e1071.

Nriagu, J.O., Pacyna, J.M., 1988. Quantitative assessment of worldwide contamina-tion of air, water and soils by trace metals. Nature 320, 735e738.

Pacyna, J.M., Pacyna, E.G., 2001. An assessment of global and regional emissions oftrace metals to the atmosphere from anthropogenic sources worldwide. Envi-ronmental Reviews 9, 269e298.

Pakkanen, T.A., Kerminen, V.M., Loukkola, K., Hillamo, R.E., Aarnio, P., Koskentalo, T.,Maenhaut, W., 2003. Size distributions of mass and chemical components instreet-level and rooftop PM1 particles in Helsinki. Atmospheric Environment37, 1673e1690.

Poschl, U., 2005. Atmospheric aerosols: composition, transformation, climate andhealth effects. Angewandte Chemie International Edition 44, 7520e7541.

Querol, X., Zhuang, X., Alastuey, A., Viana, M., Lv, W., Wang, Y., López, A., Zhu, Z.,Wei, H., Xu, S., 2006. Speciation and sources of atmospheric aerosols in a highlyindustrialised emerging mega-city in Central China. Journal of EnvironmentalMonitoring 8, 1049e1059.

Rogge, W.F., Hildemann, L.M., Mazurek, M.A., Cass, G.R., Simoneit, B.R.T., 1993.Sources of fine organic aerosol. 3. Road dust, tire debris, and organometallicbrake lining dust e roads as sources and sinks. Environmental Science &Technology 27, 1892e1904.

Sun, Y., Zhuang, G., Wang, Y., Zhao, X., Li, J., Wang, Z., An, Z., 2005. Chemicalcomposition of dust storms in Beijing and implications for the mixing ofmineral aerosol with pollution aerosol on the pathway. Journal of GeophysicalResearch 110. doi:10.1029/2005JD006054.

Sun, Y.L., Zhuang, G.S., Ying, W., Han, L.H., Guo, J.H., Mo, D., Zhang, W.J., Wang, Z.F.,Hao, Z.P., 2004. The air-borne particulate pollution in Beijing e concentration,composition, distribution and sources. Atmospheric Environment 38,5991e6004.

von Schneidemesser, E., Stone, E.A., Quraishi, T.A., Shafer, M.M., Schauer, J.J., 2010.Toxic metals in the atmosphere in Lahore, Pakistan. Science of The Total Envi-ronment 408, 1640e1648.

Wang, X., Gong, P., Zhang, Q., Yao, T., 2010. Impact of climate fluctuations ondeposition of DDT and hexachlorocyclohexane in mountain glaciers: evidencefrom ice core records. Environmental Pollution 158, 375e380.

Weckwerth, G., 2001. Verification of traffic emitted aerosol components in theambient air of Cologne (Germany). Atmospheric Environment 35, 5525e5536.

WHO, 2000. Air Quality Guidelines for Europe, p. 9. http://www.euro.who.int/air/activities/20050223_4.

Widory, D., Liu, X., Dong, S., 2010. Isotopes as tracers of sources of lead andstrontium in aerosols (TSP & PM2.5) in Beijing. Atmospheric Environment 44,3679e3687.

Wu, G., Xu, B., Yao, T., Zhang, C., Gao, S., 2009. Heavy metals in aerosol samples fromthe Eastern Pamirs collected 2004e2006. Atmospheric Research 93, 784e792.

Yang, H., Battarbee, R.W., Turner, S.D., Rose, N.L., Derwent, R.G., Wu, G., Yang, R.,2010. Historical reconstruction of mercury pollution across the Tibetan plateauusing lake sediments. Environmental Science & Technology 44, 2918e2924.

Yatkin, S., Bayram, A., 2008. Determination of major natural and anthropogenicsource profiles for particulate matter and trace elements in Izmir, Turkey.Chemosphere 71, 685e696.

Zhang, D.Z., Iwasaka, Y., Shi, G.Y., 2001. Soot particles and their impacts on the masscycle in the Tibetan atmosphere. Atmospheric Environment 35, 5883e5894.

Zheng, J., Tan, M., Shibata, Y., Tanaka, A., Li, Y., Zhang, G., Zhang, Y., Shan, Z., 2004.Characteristics of lead isotope ratios and elemental concentrations in PM10fraction of airborne particulate matter in Shanghai after the phase-out of leadedgasoline. Atmospheric Environment 38, 1191e1200.

Zhu, L., Tang, J., Lee, B., Zhang, Y., Zhang, F., 2010. Lead concentrations and isotopesin aerosols from Xiamen, China. Marine Pollution Bulletin 60, 1946e1955.