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Elemental composition of PM2.5 and PM10 at Mount Gongga in China during 2006
Atmospheric Research 93 (2009) 801–810
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Atmospheric Research j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / a t m o s
Elemental composition of PM2.5 and PM10 at Mount Gongga in China during 2006 Yang Yongjie a, Wang Yuesi a,⁎, Wen Tianxue a, Li Wei b, Zhao Ya'nan a, Li Liang a a State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China b Institute of Mountain Hazards and Environment, Chinese Academy of Sciences & Ministry of Water Conservancy, Chengdu, 610041, China
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Article history: Received 25 June 2008 Received in revised form 9 March 2009 Accepted 26 March 2009 Keywords: Aerosol Mount Gongga Seasonal variation
a b s t r a c t In order to investigate the chemical characteristics of atmospheric aerosols in a regional background site, PM2.5 and PM10 were collected at Mount Gongga Station once a week in 2006. The concentrations of fifteen elements including Na, Mg, Al, K, Ca, V, Fe, Ni, Cu, Zn, As, Ag, Ba, Tl, and Pb were detected by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The results showed that Na, Mg, Al, K, Ca, Fe were the major components of elements detected in PM2.5 and PM10, occupied 89.5% and 91.3% of all the elements. Crustal enrichment factor (EF) calculation indicated that several anthropogenic heavy metals (Ni, Cu, Zn, As, Ag, Tl, Pb) were transported long distances atmospherically. The concentrations of all elements (except Na) measured in PM2.5 and PM10 in spring and winter were higher than those in summer and autumn. The backward air mass trajectory analysis suggests that northeast India may be the source region of those pollutants. © 2009 Published by Elsevier B.V.
1. Introduction Since several years, aerosols have received increasing attention because of the roles they played in global climate change, pollution problems and health hazard. They can scatter or absorb both incoming solar radiation and thermal radiation emitted from the Earth's surface to directly change the radiation balance (Twomey, 1974; Charlson et al., 1992; Bellouin et al., 2005; Haywood and Boucher, 2000; Buseck et al., 2000). And aerosols can play as condensation nuclei (CN) for cloud droplets affecting cloud and precipitation formation to cause indirect radioactive forcing (IPCC, 2001; IPCC, 2007). Anthropogenic particles in the atmosphere can lead to serious environmental problems (Chameides et al., 1999; Dockery et al., 1993; Schwartz et al., 1996). Furthermore, aerosols can be related with serious health hazards such as increasing risks of
⁎ Corresponding author. Tel./fax: +86 10 82028726. E-mail address: [email protected] (W. Yuesi). 0169-8095/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.atmosres.2009.03.014
respiratory diseases and other diseases, leading to a higher mortality rate (Schwartz, 1993; Lee et al., 2000). In fact, the chemical composition represents a key tool for understanding the origin of particles, anthropogenic and/or natural, and for characterizing the atmospheric processes in which they are involved (Braziewicz et al., 2004; Karar and Gupta, 2007). Understanding the chemical and physical properties of regional background aerosols is useful for determining source regions, elucidating the mechanism of long-range transport of anthropogenic pollutants and validating both regional and global atmospheric models (Fattori et al., 2005; Toscano et al., 2005). Mount Gongga locates between 101°30′–102°15E and 29°20′–30°20′, in the southeast edge of Tibetan Plateau. Mount Gongga Station locates on 101°59′E and 29°35′N, 1600 meters high above sea level, built by the Chinese Academy of Sciences since 2002. Because it is relatively far from any industrialized area and lightly pullulated, Mount Gongga Station was chosen as an ideal location to monitor atmospheric component of background station (Li et al., 2005). The aim of this work is to understand the elemental composition and the characterization of particulate aerosols
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Fig. 1. Location of the sampling site.
in a regional background station. Moreover, the seasonal variation and the source of element are also discussed.
placed into plastic bags and in a freezer (−20 °C) until the transport and subsequent analysis to avoid, as much as possible, any contamination.
2. Experiment 2.2. Chemical analysis 2.1. Sampling From January to December 2006, 98 samples (PM2.5 and PM10) were collected on cellulosic filters (Whatman® 41) by using high-volume air sampler (Andersen GUV-16HBL-1). The air flow rate is 1000 l min− 1 and for each filter the sampling time is 24 h (from 8:00 am to 8:00 am of the following day). The samplers were performed on the ground in Mount Gongga Station (Fig. 1). The air volume was converted into standard condition according to the ambient conditions in the Mount Gongga region. After sampling, the filters were individually Table 1 Detection limits of ICP-MS. Element
Detection limits(μg/l)
Na Mg Al K Ca V Fe Ni Cu Zn As Ag Ba Tl Pb
1.046 0.170 0.045 1.661 1.793 0.007 2.214 0.007 0.007 0.205 0.057 0.003 0.004 0.002 0.002
Filters were digested in a 8 ml mixture of 2 ml HCl, 5 ml HNO3 and 1 ml HF by using the Microwave Accelerated Reaction System (MARS) from CEM Corporation. After digestion, the samples were evaporated to dryness at 150 °C, redissolved in 2% nitric acid before ICP-MS analysis. Elemental concentrations of PM2.5 and PM10 for Na, Mg, Al, K, Ca, V, Fe, Ni, Cu, Zn, As, Ag, Ba, Tl, and Pb were determined. Quantification was carried out by the external calibration technique using a set of external calibration standards (Agilent Corporation) at concentration levels close to that of the samples. The detection limits were given in Table 1. Procedural and field blanks were also determined and were subtracted from the samples, the Table 2 Monthly meteorological status during aerosol sampling period. Month
Temperature
R.H. (%)
Wind speed (m/s)
Precipitation (mm)
1 2 3 4 5 6 7 8 9 10 11 12
4 7.1 9.3 13.6 17.8 17.4 22.7 22.2 17.7 13.9 10.4 5.3
67.8 65.3 73.3 77 69.8 83.5 75.9 71.3 79.5 88.2 72.3 74.6
1 1.2 0.9 0.8 1 0.7 0.6 1.1 0.9 0.7 1.2 0.8
0 0 4 16.6 3 28.2 6.6 7.2 0 0 0 0.2
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Table 3 Average concentrations of elements sampled at GG in 2006 and comparison with data from other sites (ng/m3). PM10
PM2.5
Na Mg Al K Ca V Fe Ni Cu Zn As Ag Ba Tl Pb a b c
PM2.5/PM10
Mean(S.D.)
Range
Mean(S.D.)
Range
211.5(75.4) 167.8(81.2) 295.8(248.9) 498.2(312.2) 372.8(194.1) 0.7(0.4) 224.0(167.2) 0.9(0.6) 2.2(1.2) 154.6(100.6) 4.3(3.0) 0.1(0.1) 6.0(5.7) 0.3(0.2) 39.4(26.0)
101.1–559.7 20.7–356.9 11.5–1068.9 128.9–2187.7 54.4–888.30.0–2.2 3.2–748.3 0.0–2.7 0.0–5.7 9.8–410.3 0.7–17.3 0.0–0.4 0.5–39.8 0.0–0.9 9.0–112.8
320.4(128.2) 327.6(165.3) 688.4(552.3) 765.0(448.2) 848.6(506.8) 1.4(1.0) 496.8(360.2) 1.6(1.2) 3.6(1.9) 247.6(166.4) 6.1(4.1) 0.2(0.1) 12.0(10.3) 0.4(0.2) 55.3(37.5)
137.6–831.9 59.5–760.2 60.3–2468.3 211.0–3043.7 126.4–2462.9 0.2–5.2 19.6–1764.2 0.0–6.8 0.1–7.6 11.9–685.2 1.3–24.7 0.0–0.5 2.1–66.0 0.1–1.2 11.8–169.7
0.66 0.51 0.43 0.65 0.44 0.50 0.45 0.56 0.61 0.62 0.70 0.50 0.50 0.75 0.71
Waliguan a
2110–3410 1190–2200 2010–4280 3.02–5.88 1720–3910
9.5–26.3 0.70–3.37 21.3–45.3
Lin'an b
Hong Kong c
1534.84 295.53 4461.14 2802.94 7036.86 5.88 1974.59 3.14 13.72 160.79 0.70 0.53 49.13
2580 340 700 1510 2170 5.12 860 8.62 35.38
263.98
7.28
98.74
TSP collected at Waliguan, Northeast Tibetan Plateau, 1992–1995 (Wen et al., 2001). TSP collected at Lin'an, air pollution background site in Zhejiang province, 1991 (Yang et al., 1995). PM10 collected in Hung Hom of Hong Kong from November 2000 to February 2001 (K.F. Ho et al., 2003).
concentrations of Na, Mg, Al, K, Ca, and Fe in blank filters were 5% less than those in samples, and V, Ni, Cu, Zn, As, Ag, Ba, Tl, and Pb were 3% less than those in samples. The blanks were taken every month (about 8 samples). 2.3. Meteorological data An automatic weather station was placed at Mount Gongga Station. Meteorological parameters (Table 2), including air temperature, wind speed, precipitation, air and relative humidity were measured simultaneously. 3. Result and discussion 3.1. Average elemental concentrations of PM2.5 and PM10 at Mount Gongga in 2006 Mean elemental compositions of PM2.5 and PM10 collected at Mount Gongga through the sampling period were given in Table 3, and the mean elemental compositions of aerosol particles from other sites were also tabulated in Table 3 for comparison. Na, Mg, Al, K, Ca, and Fe were the major elements
detected in PM2.5 and PM10, occupied 89.5% and 91.3% of all the elements. For Na, Mg, Al, K, Ca, and Fe, high concentrations are not surprising, because they are commonly found in the crustal origin elements, which constitute the major proportion in the measurements of PM. Typical crustal elements like Al, Ca, and Fe were dominant in coarse particles, and the values of PM2.5/PM10 were 0.43, 0.44 and 0.45, respectively. Pb, Tl, As, Zn, Cu, and Ni, pollution elements, mainly appeared in fine particles, and the ratios were respectively 0.71, 0.75, 0.70, 0.62, 0.61, and 0.56. Sodium and potassium were mainly contained in fine particles, Na possibly affected by sea salt, K in fine particles comes from biomass burning. Waliguan (N361170, E1001540, 3810 m a.s.l.), located at the Northeast Tibetan Plateau, is a Global Atmosphere Watch (GAW) station. From 1992 to 1995, aerosol samples were collected at Waliguan and then analyzed by PIXE and neutron activation analysis (Wen et al., 2001). Compared with TSP of Waliguan, MG has a low mass concentration of crustal elements as Al, Ca, and Fe in PM10 (Table 2), and has a significant high mass concentrations of pollution elements as Zn and As in PM10. Waliguan is closer to big deserts in the northwest China so it has
Fig. 2. Enrichment factors of elements against average crustal composition at Mount Gongga.
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Fig. 3. Weekly concentrations of elements in the aerosol of Mount Gongga, from January 2006 to December 2006.
Y. Yongjie et al. / Atmospheric Research 93 (2009) 801–810
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Fig. 3 (continued ).
a higher dust load to increase the concentrations of crustal elements. Moreover, the emission of atmospheric pollutant in Tibetan Plateau is scare. Mount Gongga station is in the forest, the vegetation is flourishing there, so the soil source is relatively reduced. The concentrations of Zn and As mean that Mount Gongga station receives more anthropogenic air pollutant. Lin'an, air pollution background site (WMO station), is located in the Zhejiang province. The concentrations of the elements at MG are distinctly lower than those of Lin'an except Zn and As. But the mean Zn concentration in PM2.5 is approximately as much as that reported in TSP of Lin'an. Furthermore, the mean As concentration is approximately 10 times higher than that reported in TSP of Lin'an. Hong Kong is typical urban site. For all elements, average concentrations in Mount Gongga station are lower than those in Hong Kong. Because the site is located in the Nature Reserve, the local population in Mount Gongga region is very limited and the local emission of atmospheric pollutant is scare. So the low elemental concentrations in PM2.5 and PM10 comparing with urban site should be reasonable. But the high elemental concentrations in PM2.5 and PM10 for some pollution elements like Zn, As in PM2.5 and PM10 in Mount Gongga station appeared during the sampling period,
that means aerosols maybe strongly affected from the whole region by long-distance transportation. 3.2. Enrichment factors (EFs) The EF of elements in aerosols relative to the crustal material is often calculated to identify source regions and evaluate the degree of anthropogenic influence (Duce et al., 1975; Zoller et al., 1974), which is defined as follows: EFX = ðCX =CR Þaerosol = ðCX = CR Þcrust ; where X represents the element of interest; EFX the EF of X; CX the concentration of X, and CR the concentration of a reference element. The aerosol and crust subscripts refer to particles in the aerosol samples and crustal material, respectively. If the EFX approaches unity, the crustal source is the dominant source for the element X, if EFX is N10, the element X may have a significant fraction from noncrustal sources. Al was selected as the reference material for our EF calculation. Taylor and McLennan's (1995) average upper continental crust composition was used as the elemental composition of the crust material.
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Fig. 2 shows the averages of the EFs of elements in PM2.5 and PM10 collected at Mount Gongga station. The EFs of Na, Mg, K, Ca, V, Fe, and Ba were all below 5 in both PM2.5 and PM10, suggesting that they were attributable predominantly to soil
and dust. However, much higher EFs, ranging from tens to hundreds, were found for the elements Ni, Cu, Zn, As, Ag, Tl, and Pb in PM2.5. Compared with those in PM2.5, relatively lower EFs of pollution elements, ranging from tens to hundreds, were
Fig. 4. Seasonal variation of elemental concentrations of PM2.5 and PM10 at Mount Gongga in 2006.
Y. Yongjie et al. / Atmospheric Research 93 (2009) 801–810
807
Fig. 4 (continued ).
observed in PM10. Previous studies showed that such enriched elements can originate from a wide variety of anthropogenic sources. Nriagu and Pacyna (1988) have pointed out that the major sources of Cu on atmospheric particles in the globe are combustion of fossil fuels, industrial metallurgical process and waste incineration. Zn may also be derived from similar sources, or other traffic-related sources (Chueinta et al., 2000; Rogge et al., 1993). As is a known component in coal combustion (Teresa et al., 2007). Besides industry emission, motor vehicle emission, and coal burning, long-range transported dust and the re-suspended soil containing the deposition of those from previously emitted leaded gasoline could be the important sources of Pb (Yele et al., 2006). In light of the very little local emission of industrial pollutants, it is suggested such trace elements might be long-range transported into Mount Gongga station by atmospheric circulation. 3.3. Weekly and seasonal variations of elemental concentrations of PM2.5 and PM10 at Mount Gongga in 2006 Fig. 3 shows the concentrations of fifteen elements (Na, Mg, Al, K, Ca, V, Fe, Ni, Cu, Zn, As, Ag, Ba, Tl and Pb) in PM10 and PM2.5 collected at Mount Gongga station as a function of the time when samples were collected. The concentrations of these elements showed significant variations from week to
week. The concentrations in PM10 and PM2.5 varied greatly, because of the meteorological factors, such as temperature, relative humidity, and wind speed, which favor or adversely affect the dispersion of pollutants. In addition, air mass from different regions brings different pollutants. The seasonal variation of various elements in PM10 and PM2.5 of Mount Gongga station is shown in Fig. 4 and Table 4. Spring is from March to May, summer is from June to August, autumn is from September to November, and winter is from December to February. Overall, the concentrations of those elements in PM10 and PM2.5 (except Na in PM2.5) measured in spring and winter were higher than those in summer and winter. The average concentrations of Na, Mg, Al, K, Ca, Ni, Zn, Ag, and Tl in PM10 in spring were the highest ones, and Fe, V, Cu, As, Ba, and Pb in winter were the highest ones. The average concentrations of Na, Al, K, Ca, V, Fe, Ni, Cu, and Ba in PM10 in autumn were the lowest ones, and Mg, Zn, As, Ag, Tl, and Pb in summer were the lowest ones. The average concentrations of Mg, Al, K, Ca, Fe, Cu, As, Ba, Tl, and Pb in PM2.5 in winter were the highest ones, and V, Ni, Zn, and Ag in spring were the highest ones. The average concentrations of Mg, K, Zn, As, Ag, Tl, and Pb in PM2.5 in summer were the lowest ones, and Al, Ca, V, Fe, Ni, Cu, and Ba in autumn were the lowest ones. Because of no obvious local pollution source for the site, the aerosol possibly came from the regional sources of aerosol. In
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Table 4 Seasonal variation of various elements in PM10 and PM2.5 of GG (ng/m3). PM10
Element
PM2.5 Spring
Summer
Autumn
Winter
Spring
Summer
Autumn
Winter
Na Mg Al K Ca V Fe Ni Cu Zn As Ag Ba Tl Pb
206.3 147.6 348.8 555.0 389.6 0.9 268.5 1.1 2.5 218.5 4.6 0.1 6.2 0.3 44.3
206.6 130.8 215.4 396.4 290.0 0.5 186.3 1.0 2.1 74.8 2.7 0.1 4.4 0.2 22.5
215.6 184.0 126.1 394.1 280.4 0.4 93.5 0.6 1.3 146.1 3.8 0.1 3.9 0.2 33.7
207.1 199.8 497.6 605.4 521.8 0.8 352.0 1.0 3.1 168.4 5.4 0.1 9.6 0.4 53.1
350.1 373.6 978.7 912.3 1117.3 1.7 652.3 2.3 4.1 359.7 7.0 0.2 15.0 0.5 68.3
303.0 247.7 516.5 628.2 629.9 1.0 414.4 1.7 3.7 120.9 3.7 0.1 8.4 0.2 30.4
279.2 301.6 267.1 569.7 555.3 0.8 205.2 0.8 2.1 227.1 5.4 0.1 6.7 0.3 46.2
323.1 369.2 973.1 893.0 1051.7 1.8 697.5 1.7 4.7 265.1 7.2 0.2 17.2 0.4 72.5
order to investigate potential regional sources of aerosol and transport pathways of air masses, 3-day backward trajectories were computed using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT-4) model developed by the National Oceanic and Atmospheric Administration (Draxler and Hess, 1997) (http://www.arl.noaa.gov/ready/hysplit4. html). Meteorological data fields to run the model are available from the US National Centers for Environmental Prediction (NCEP) global data assimilation system (GDAS) which is called
the final run (FNL) data. The trajectories were calculated at an altitude of 500 m Above Ground Level (AGL) every sampling day in 2006, and the results ware shown in Fig. 5. Totally, the air mass was from different directions in different seasons. Air parcels arriving at Mount Gongga station in winter and autumn are mainly from Tibetan Plateau and northeast India. The concentrations of crustal elements in Waliguan are much higher than those of this study, and those elements are brought to Mount Gongga station in winter and summer by air
Fig. 5. 72-hour back trajectories of the sampling periods of Mount Gongga (one trajectory every 72 h): a) spring; b) summer; c) autumn; d) winter.
Y. Yongjie et al. / Atmospheric Research 93 (2009) 801–810
mass. It has been reported that the air pollution is serious in northeast India (Begum et al., 2004; Salam et al., 2003), which favor the high concentrations of pollution elements at Mount Gongga station. In summer, the air mass mainly comes from southeast Sichuan province, in which there are strong sources of PM10 and PM2.5. But summer is a wet season at Mount Gongga station, so the wet deposition of aerosol is strong. And that is the reason for the lowest average concentrations of the airborne elements in summer at Mount Gongga station. The autumn was the transitional season at Mount Gongga station, and the wind direction was not as steady as the other seasons. That is the reason for high concentrations of some elements and low concentrations of the others. 4. Conclusion (1) Elemental compositions of PM2.5 and PM10 collected in2006 at Mount Gongga Station, a regional background site in the inland Tibetan Plateau, were preliminary characterized. It was found that Na, Mg, Al, K, Ca, Fe and Fe were major elements in PM2.5 and PM10. Compared with the data from other sites, Mount Gongga is strongly affected by regional aerosols and suitable to monitor the chemistry of the whole region. (2) According to enrichment factor calculations, Na, Al, Mg, K, Ca, V, Fe, and Ba in PM2.5 and PM10 mainly originate from crust material, and Ni, Cu, Zn, As, Ag, Tl, and Pb in PM2.5 relatively higher than that in PM10 appear to be related to the long-range transport of anthropogenic pollutant. (3) All the analyzed elements in PM2.5 and PM10 except Na in PM2.5 displayed strong seasonal variations: the elemental concentrations were higher in spring and winter than those in summer and autumn. Investigation using backward air mass trajectory indicates that air masses in Mount Gongga station come predominantly from Tibetan Plateau and northeast India during spring and winter. Therefore, the pollutants from northeast Asia and crustal materials from Tibetan Plateau, appear to be transported to Mount Gongga. Acknowledgements This work was supported by the grant of the National Basic Research Program (2007CB407303), the Knowledge Innovation Program of the Chinese Academy of Sciences (approved # KZCX1-YW-06-01) and the National High Technology Research and Development Program of China (2006AA06A301). The authors would like to thank the CERN observation team for their maintenance work. References Begum, B.A., Kim, E., Biswas, S.K., Hopke, P.K., 2004. Investigation of sources of atmospheric aerosol at urban and semi-urban areas in Bangladesh. Atmospheric Environment 38 (19), 3025–3038. Bellouin, N., Boucher, O., Haywood, J., Reddy, M.S., 2005. Global estimate of aerosol direct radiative forcing from satellite measurements. Nature 438 (7071), 1138–1141. Braziewicz, J., Kownacka, L., Majewska, U., Korman, A., 2004. Elemental concentrations in tropospheric and lower stratospheric air in a Northeastern region of Poland. Atmospheric Environment 38 (13), 1989–1996.
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Elemental composition of PM2.5 and PM10 at Mount Gongga in China during 2006 Yang Yongjie a, Wang Yuesi a,⁎, Wen Tianxue a, Li Wei b, Zhao Ya'nan a, Li Liang a a State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China b Institute of Mountain Hazards and Environment, Chinese Academy of Sciences & Ministry of Water Conservancy, Chengdu, 610041, China
a r t i c l e
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Article history: Received 25 June 2008 Received in revised form 9 March 2009 Accepted 26 March 2009 Keywords: Aerosol Mount Gongga Seasonal variation
a b s t r a c t In order to investigate the chemical characteristics of atmospheric aerosols in a regional background site, PM2.5 and PM10 were collected at Mount Gongga Station once a week in 2006. The concentrations of fifteen elements including Na, Mg, Al, K, Ca, V, Fe, Ni, Cu, Zn, As, Ag, Ba, Tl, and Pb were detected by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The results showed that Na, Mg, Al, K, Ca, Fe were the major components of elements detected in PM2.5 and PM10, occupied 89.5% and 91.3% of all the elements. Crustal enrichment factor (EF) calculation indicated that several anthropogenic heavy metals (Ni, Cu, Zn, As, Ag, Tl, Pb) were transported long distances atmospherically. The concentrations of all elements (except Na) measured in PM2.5 and PM10 in spring and winter were higher than those in summer and autumn. The backward air mass trajectory analysis suggests that northeast India may be the source region of those pollutants. © 2009 Published by Elsevier B.V.
1. Introduction Since several years, aerosols have received increasing attention because of the roles they played in global climate change, pollution problems and health hazard. They can scatter or absorb both incoming solar radiation and thermal radiation emitted from the Earth's surface to directly change the radiation balance (Twomey, 1974; Charlson et al., 1992; Bellouin et al., 2005; Haywood and Boucher, 2000; Buseck et al., 2000). And aerosols can play as condensation nuclei (CN) for cloud droplets affecting cloud and precipitation formation to cause indirect radioactive forcing (IPCC, 2001; IPCC, 2007). Anthropogenic particles in the atmosphere can lead to serious environmental problems (Chameides et al., 1999; Dockery et al., 1993; Schwartz et al., 1996). Furthermore, aerosols can be related with serious health hazards such as increasing risks of
⁎ Corresponding author. Tel./fax: +86 10 82028726. E-mail address: [email protected] (W. Yuesi). 0169-8095/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.atmosres.2009.03.014
respiratory diseases and other diseases, leading to a higher mortality rate (Schwartz, 1993; Lee et al., 2000). In fact, the chemical composition represents a key tool for understanding the origin of particles, anthropogenic and/or natural, and for characterizing the atmospheric processes in which they are involved (Braziewicz et al., 2004; Karar and Gupta, 2007). Understanding the chemical and physical properties of regional background aerosols is useful for determining source regions, elucidating the mechanism of long-range transport of anthropogenic pollutants and validating both regional and global atmospheric models (Fattori et al., 2005; Toscano et al., 2005). Mount Gongga locates between 101°30′–102°15E and 29°20′–30°20′, in the southeast edge of Tibetan Plateau. Mount Gongga Station locates on 101°59′E and 29°35′N, 1600 meters high above sea level, built by the Chinese Academy of Sciences since 2002. Because it is relatively far from any industrialized area and lightly pullulated, Mount Gongga Station was chosen as an ideal location to monitor atmospheric component of background station (Li et al., 2005). The aim of this work is to understand the elemental composition and the characterization of particulate aerosols
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Fig. 1. Location of the sampling site.
in a regional background station. Moreover, the seasonal variation and the source of element are also discussed.
placed into plastic bags and in a freezer (−20 °C) until the transport and subsequent analysis to avoid, as much as possible, any contamination.
2. Experiment 2.2. Chemical analysis 2.1. Sampling From January to December 2006, 98 samples (PM2.5 and PM10) were collected on cellulosic filters (Whatman® 41) by using high-volume air sampler (Andersen GUV-16HBL-1). The air flow rate is 1000 l min− 1 and for each filter the sampling time is 24 h (from 8:00 am to 8:00 am of the following day). The samplers were performed on the ground in Mount Gongga Station (Fig. 1). The air volume was converted into standard condition according to the ambient conditions in the Mount Gongga region. After sampling, the filters were individually Table 1 Detection limits of ICP-MS. Element
Detection limits(μg/l)
Na Mg Al K Ca V Fe Ni Cu Zn As Ag Ba Tl Pb
1.046 0.170 0.045 1.661 1.793 0.007 2.214 0.007 0.007 0.205 0.057 0.003 0.004 0.002 0.002
Filters were digested in a 8 ml mixture of 2 ml HCl, 5 ml HNO3 and 1 ml HF by using the Microwave Accelerated Reaction System (MARS) from CEM Corporation. After digestion, the samples were evaporated to dryness at 150 °C, redissolved in 2% nitric acid before ICP-MS analysis. Elemental concentrations of PM2.5 and PM10 for Na, Mg, Al, K, Ca, V, Fe, Ni, Cu, Zn, As, Ag, Ba, Tl, and Pb were determined. Quantification was carried out by the external calibration technique using a set of external calibration standards (Agilent Corporation) at concentration levels close to that of the samples. The detection limits were given in Table 1. Procedural and field blanks were also determined and were subtracted from the samples, the Table 2 Monthly meteorological status during aerosol sampling period. Month
Temperature
R.H. (%)
Wind speed (m/s)
Precipitation (mm)
1 2 3 4 5 6 7 8 9 10 11 12
4 7.1 9.3 13.6 17.8 17.4 22.7 22.2 17.7 13.9 10.4 5.3
67.8 65.3 73.3 77 69.8 83.5 75.9 71.3 79.5 88.2 72.3 74.6
1 1.2 0.9 0.8 1 0.7 0.6 1.1 0.9 0.7 1.2 0.8
0 0 4 16.6 3 28.2 6.6 7.2 0 0 0 0.2
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Table 3 Average concentrations of elements sampled at GG in 2006 and comparison with data from other sites (ng/m3). PM10
PM2.5
Na Mg Al K Ca V Fe Ni Cu Zn As Ag Ba Tl Pb a b c
PM2.5/PM10
Mean(S.D.)
Range
Mean(S.D.)
Range
211.5(75.4) 167.8(81.2) 295.8(248.9) 498.2(312.2) 372.8(194.1) 0.7(0.4) 224.0(167.2) 0.9(0.6) 2.2(1.2) 154.6(100.6) 4.3(3.0) 0.1(0.1) 6.0(5.7) 0.3(0.2) 39.4(26.0)
101.1–559.7 20.7–356.9 11.5–1068.9 128.9–2187.7 54.4–888.30.0–2.2 3.2–748.3 0.0–2.7 0.0–5.7 9.8–410.3 0.7–17.3 0.0–0.4 0.5–39.8 0.0–0.9 9.0–112.8
320.4(128.2) 327.6(165.3) 688.4(552.3) 765.0(448.2) 848.6(506.8) 1.4(1.0) 496.8(360.2) 1.6(1.2) 3.6(1.9) 247.6(166.4) 6.1(4.1) 0.2(0.1) 12.0(10.3) 0.4(0.2) 55.3(37.5)
137.6–831.9 59.5–760.2 60.3–2468.3 211.0–3043.7 126.4–2462.9 0.2–5.2 19.6–1764.2 0.0–6.8 0.1–7.6 11.9–685.2 1.3–24.7 0.0–0.5 2.1–66.0 0.1–1.2 11.8–169.7
0.66 0.51 0.43 0.65 0.44 0.50 0.45 0.56 0.61 0.62 0.70 0.50 0.50 0.75 0.71
Waliguan a
2110–3410 1190–2200 2010–4280 3.02–5.88 1720–3910
9.5–26.3 0.70–3.37 21.3–45.3
Lin'an b
Hong Kong c
1534.84 295.53 4461.14 2802.94 7036.86 5.88 1974.59 3.14 13.72 160.79 0.70 0.53 49.13
2580 340 700 1510 2170 5.12 860 8.62 35.38
263.98
7.28
98.74
TSP collected at Waliguan, Northeast Tibetan Plateau, 1992–1995 (Wen et al., 2001). TSP collected at Lin'an, air pollution background site in Zhejiang province, 1991 (Yang et al., 1995). PM10 collected in Hung Hom of Hong Kong from November 2000 to February 2001 (K.F. Ho et al., 2003).
concentrations of Na, Mg, Al, K, Ca, and Fe in blank filters were 5% less than those in samples, and V, Ni, Cu, Zn, As, Ag, Ba, Tl, and Pb were 3% less than those in samples. The blanks were taken every month (about 8 samples). 2.3. Meteorological data An automatic weather station was placed at Mount Gongga Station. Meteorological parameters (Table 2), including air temperature, wind speed, precipitation, air and relative humidity were measured simultaneously. 3. Result and discussion 3.1. Average elemental concentrations of PM2.5 and PM10 at Mount Gongga in 2006 Mean elemental compositions of PM2.5 and PM10 collected at Mount Gongga through the sampling period were given in Table 3, and the mean elemental compositions of aerosol particles from other sites were also tabulated in Table 3 for comparison. Na, Mg, Al, K, Ca, and Fe were the major elements
detected in PM2.5 and PM10, occupied 89.5% and 91.3% of all the elements. For Na, Mg, Al, K, Ca, and Fe, high concentrations are not surprising, because they are commonly found in the crustal origin elements, which constitute the major proportion in the measurements of PM. Typical crustal elements like Al, Ca, and Fe were dominant in coarse particles, and the values of PM2.5/PM10 were 0.43, 0.44 and 0.45, respectively. Pb, Tl, As, Zn, Cu, and Ni, pollution elements, mainly appeared in fine particles, and the ratios were respectively 0.71, 0.75, 0.70, 0.62, 0.61, and 0.56. Sodium and potassium were mainly contained in fine particles, Na possibly affected by sea salt, K in fine particles comes from biomass burning. Waliguan (N361170, E1001540, 3810 m a.s.l.), located at the Northeast Tibetan Plateau, is a Global Atmosphere Watch (GAW) station. From 1992 to 1995, aerosol samples were collected at Waliguan and then analyzed by PIXE and neutron activation analysis (Wen et al., 2001). Compared with TSP of Waliguan, MG has a low mass concentration of crustal elements as Al, Ca, and Fe in PM10 (Table 2), and has a significant high mass concentrations of pollution elements as Zn and As in PM10. Waliguan is closer to big deserts in the northwest China so it has
Fig. 2. Enrichment factors of elements against average crustal composition at Mount Gongga.
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Fig. 3. Weekly concentrations of elements in the aerosol of Mount Gongga, from January 2006 to December 2006.
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Fig. 3 (continued ).
a higher dust load to increase the concentrations of crustal elements. Moreover, the emission of atmospheric pollutant in Tibetan Plateau is scare. Mount Gongga station is in the forest, the vegetation is flourishing there, so the soil source is relatively reduced. The concentrations of Zn and As mean that Mount Gongga station receives more anthropogenic air pollutant. Lin'an, air pollution background site (WMO station), is located in the Zhejiang province. The concentrations of the elements at MG are distinctly lower than those of Lin'an except Zn and As. But the mean Zn concentration in PM2.5 is approximately as much as that reported in TSP of Lin'an. Furthermore, the mean As concentration is approximately 10 times higher than that reported in TSP of Lin'an. Hong Kong is typical urban site. For all elements, average concentrations in Mount Gongga station are lower than those in Hong Kong. Because the site is located in the Nature Reserve, the local population in Mount Gongga region is very limited and the local emission of atmospheric pollutant is scare. So the low elemental concentrations in PM2.5 and PM10 comparing with urban site should be reasonable. But the high elemental concentrations in PM2.5 and PM10 for some pollution elements like Zn, As in PM2.5 and PM10 in Mount Gongga station appeared during the sampling period,
that means aerosols maybe strongly affected from the whole region by long-distance transportation. 3.2. Enrichment factors (EFs) The EF of elements in aerosols relative to the crustal material is often calculated to identify source regions and evaluate the degree of anthropogenic influence (Duce et al., 1975; Zoller et al., 1974), which is defined as follows: EFX = ðCX =CR Þaerosol = ðCX = CR Þcrust ; where X represents the element of interest; EFX the EF of X; CX the concentration of X, and CR the concentration of a reference element. The aerosol and crust subscripts refer to particles in the aerosol samples and crustal material, respectively. If the EFX approaches unity, the crustal source is the dominant source for the element X, if EFX is N10, the element X may have a significant fraction from noncrustal sources. Al was selected as the reference material for our EF calculation. Taylor and McLennan's (1995) average upper continental crust composition was used as the elemental composition of the crust material.
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Fig. 2 shows the averages of the EFs of elements in PM2.5 and PM10 collected at Mount Gongga station. The EFs of Na, Mg, K, Ca, V, Fe, and Ba were all below 5 in both PM2.5 and PM10, suggesting that they were attributable predominantly to soil
and dust. However, much higher EFs, ranging from tens to hundreds, were found for the elements Ni, Cu, Zn, As, Ag, Tl, and Pb in PM2.5. Compared with those in PM2.5, relatively lower EFs of pollution elements, ranging from tens to hundreds, were
Fig. 4. Seasonal variation of elemental concentrations of PM2.5 and PM10 at Mount Gongga in 2006.
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Fig. 4 (continued ).
observed in PM10. Previous studies showed that such enriched elements can originate from a wide variety of anthropogenic sources. Nriagu and Pacyna (1988) have pointed out that the major sources of Cu on atmospheric particles in the globe are combustion of fossil fuels, industrial metallurgical process and waste incineration. Zn may also be derived from similar sources, or other traffic-related sources (Chueinta et al., 2000; Rogge et al., 1993). As is a known component in coal combustion (Teresa et al., 2007). Besides industry emission, motor vehicle emission, and coal burning, long-range transported dust and the re-suspended soil containing the deposition of those from previously emitted leaded gasoline could be the important sources of Pb (Yele et al., 2006). In light of the very little local emission of industrial pollutants, it is suggested such trace elements might be long-range transported into Mount Gongga station by atmospheric circulation. 3.3. Weekly and seasonal variations of elemental concentrations of PM2.5 and PM10 at Mount Gongga in 2006 Fig. 3 shows the concentrations of fifteen elements (Na, Mg, Al, K, Ca, V, Fe, Ni, Cu, Zn, As, Ag, Ba, Tl and Pb) in PM10 and PM2.5 collected at Mount Gongga station as a function of the time when samples were collected. The concentrations of these elements showed significant variations from week to
week. The concentrations in PM10 and PM2.5 varied greatly, because of the meteorological factors, such as temperature, relative humidity, and wind speed, which favor or adversely affect the dispersion of pollutants. In addition, air mass from different regions brings different pollutants. The seasonal variation of various elements in PM10 and PM2.5 of Mount Gongga station is shown in Fig. 4 and Table 4. Spring is from March to May, summer is from June to August, autumn is from September to November, and winter is from December to February. Overall, the concentrations of those elements in PM10 and PM2.5 (except Na in PM2.5) measured in spring and winter were higher than those in summer and winter. The average concentrations of Na, Mg, Al, K, Ca, Ni, Zn, Ag, and Tl in PM10 in spring were the highest ones, and Fe, V, Cu, As, Ba, and Pb in winter were the highest ones. The average concentrations of Na, Al, K, Ca, V, Fe, Ni, Cu, and Ba in PM10 in autumn were the lowest ones, and Mg, Zn, As, Ag, Tl, and Pb in summer were the lowest ones. The average concentrations of Mg, Al, K, Ca, Fe, Cu, As, Ba, Tl, and Pb in PM2.5 in winter were the highest ones, and V, Ni, Zn, and Ag in spring were the highest ones. The average concentrations of Mg, K, Zn, As, Ag, Tl, and Pb in PM2.5 in summer were the lowest ones, and Al, Ca, V, Fe, Ni, Cu, and Ba in autumn were the lowest ones. Because of no obvious local pollution source for the site, the aerosol possibly came from the regional sources of aerosol. In
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Table 4 Seasonal variation of various elements in PM10 and PM2.5 of GG (ng/m3). PM10
Element
PM2.5 Spring
Summer
Autumn
Winter
Spring
Summer
Autumn
Winter
Na Mg Al K Ca V Fe Ni Cu Zn As Ag Ba Tl Pb
206.3 147.6 348.8 555.0 389.6 0.9 268.5 1.1 2.5 218.5 4.6 0.1 6.2 0.3 44.3
206.6 130.8 215.4 396.4 290.0 0.5 186.3 1.0 2.1 74.8 2.7 0.1 4.4 0.2 22.5
215.6 184.0 126.1 394.1 280.4 0.4 93.5 0.6 1.3 146.1 3.8 0.1 3.9 0.2 33.7
207.1 199.8 497.6 605.4 521.8 0.8 352.0 1.0 3.1 168.4 5.4 0.1 9.6 0.4 53.1
350.1 373.6 978.7 912.3 1117.3 1.7 652.3 2.3 4.1 359.7 7.0 0.2 15.0 0.5 68.3
303.0 247.7 516.5 628.2 629.9 1.0 414.4 1.7 3.7 120.9 3.7 0.1 8.4 0.2 30.4
279.2 301.6 267.1 569.7 555.3 0.8 205.2 0.8 2.1 227.1 5.4 0.1 6.7 0.3 46.2
323.1 369.2 973.1 893.0 1051.7 1.8 697.5 1.7 4.7 265.1 7.2 0.2 17.2 0.4 72.5
order to investigate potential regional sources of aerosol and transport pathways of air masses, 3-day backward trajectories were computed using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT-4) model developed by the National Oceanic and Atmospheric Administration (Draxler and Hess, 1997) (http://www.arl.noaa.gov/ready/hysplit4. html). Meteorological data fields to run the model are available from the US National Centers for Environmental Prediction (NCEP) global data assimilation system (GDAS) which is called
the final run (FNL) data. The trajectories were calculated at an altitude of 500 m Above Ground Level (AGL) every sampling day in 2006, and the results ware shown in Fig. 5. Totally, the air mass was from different directions in different seasons. Air parcels arriving at Mount Gongga station in winter and autumn are mainly from Tibetan Plateau and northeast India. The concentrations of crustal elements in Waliguan are much higher than those of this study, and those elements are brought to Mount Gongga station in winter and summer by air
Fig. 5. 72-hour back trajectories of the sampling periods of Mount Gongga (one trajectory every 72 h): a) spring; b) summer; c) autumn; d) winter.
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mass. It has been reported that the air pollution is serious in northeast India (Begum et al., 2004; Salam et al., 2003), which favor the high concentrations of pollution elements at Mount Gongga station. In summer, the air mass mainly comes from southeast Sichuan province, in which there are strong sources of PM10 and PM2.5. But summer is a wet season at Mount Gongga station, so the wet deposition of aerosol is strong. And that is the reason for the lowest average concentrations of the airborne elements in summer at Mount Gongga station. The autumn was the transitional season at Mount Gongga station, and the wind direction was not as steady as the other seasons. That is the reason for high concentrations of some elements and low concentrations of the others. 4. Conclusion (1) Elemental compositions of PM2.5 and PM10 collected in2006 at Mount Gongga Station, a regional background site in the inland Tibetan Plateau, were preliminary characterized. It was found that Na, Mg, Al, K, Ca, Fe and Fe were major elements in PM2.5 and PM10. Compared with the data from other sites, Mount Gongga is strongly affected by regional aerosols and suitable to monitor the chemistry of the whole region. (2) According to enrichment factor calculations, Na, Al, Mg, K, Ca, V, Fe, and Ba in PM2.5 and PM10 mainly originate from crust material, and Ni, Cu, Zn, As, Ag, Tl, and Pb in PM2.5 relatively higher than that in PM10 appear to be related to the long-range transport of anthropogenic pollutant. (3) All the analyzed elements in PM2.5 and PM10 except Na in PM2.5 displayed strong seasonal variations: the elemental concentrations were higher in spring and winter than those in summer and autumn. Investigation using backward air mass trajectory indicates that air masses in Mount Gongga station come predominantly from Tibetan Plateau and northeast India during spring and winter. Therefore, the pollutants from northeast Asia and crustal materials from Tibetan Plateau, appear to be transported to Mount Gongga. Acknowledgements This work was supported by the grant of the National Basic Research Program (2007CB407303), the Knowledge Innovation Program of the Chinese Academy of Sciences (approved # KZCX1-YW-06-01) and the National High Technology Research and Development Program of China (2006AA06A301). The authors would like to thank the CERN observation team for their maintenance work. References Begum, B.A., Kim, E., Biswas, S.K., Hopke, P.K., 2004. Investigation of sources of atmospheric aerosol at urban and semi-urban areas in Bangladesh. Atmospheric Environment 38 (19), 3025–3038. Bellouin, N., Boucher, O., Haywood, J., Reddy, M.S., 2005. Global estimate of aerosol direct radiative forcing from satellite measurements. Nature 438 (7071), 1138–1141. Braziewicz, J., Kownacka, L., Majewska, U., Korman, A., 2004. Elemental concentrations in tropospheric and lower stratospheric air in a Northeastern region of Poland. Atmospheric Environment 38 (13), 1989–1996.
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