Journal of Geochemical Exploration 111 (2011) 138–151

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Journal of Geochemical Exploration

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Spatio-temporal occurrences and mineralogical–geochemical characteristics ofairborne dusts in Khuzestan Province (southwestern Iran)

A. Zarasvandi a,⁎, E.J.M. Carranza b, F. Moore c, F. Rastmanesh a

a Department of Geology, Shahid Chamran University, Ahvaz, Iranb Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, The Netherlandsc Department of Earth Sciences, Shiraz University, Shiraz, Iran

⁎ Corresponding author. Fax: +98 611 3331059.E-mail address: zarasvandi_a@scu.ac.ir (A. Zarasvan

0375-6742/$ – see front matter © 2011 Elsevier B.V. Adoi:10.1016/j.gexplo.2011.04.004

a b s t r a c t

a r t i c l e i n f o

Article history:Received 9 September 2010Accepted 7 April 2011Available online 14 April 2011

Keywords:Airborne dustTransportEnrichment factorGeological sourceKhuzestan (Iran)

Dust storms in Khuzestan province (Iran) are causing problems in industries and human health. To mitigatethe impact of those phenomena, it is vital to know the physical and chemical characteristics of airborne dusts.In this paper, we give an overview of the spatio-temporal occurrences and geochemical characteristics ofairborne dusts in Khuzestan. Meteorological data from 10 stations in Khuzestan during 1996–2009 indicate(a) an average of 47 dust storm days per year, (b) a lowest annual average of 13 dust storm days in 1998, (c) ahighest annual average of 104 dust storm days in 2008, and (d) an average increase of two dust storm days peryear. Above-average number of dust storm days usually occurred in the cities of Dezful, Ahvaz, Masjed-e-Soleiman, Abadan and Bostan, whereas below-average number of dust storm days usually occurred in thecities of Mahshahr, Ramhormoz, Behbahan, Shoushtar and Izeh. XRD analyses of airborne dust samplescollected in 2008 and 2009 show that the mineralogy of airborne dusts is dominated by calcite, followed byquartz and then kaolinite, with minor gypsum. SEM analyses of the samples indicate that airborne dusts haverounded irregular, prismatic and rhombic shapes. The sizes of airborne dusts vary from 2 to 52 μm, but 10 to22 μm are the dominant sizes. The smallest and largest dust particles are clays, sulfates or carbonates. XRF andICP analyses of the samples show that the most important oxide compositions of airborne dusts are SiO2,Al2O3, Fe2O3, CaO and MgO. Estimates of enrichment factors (EF) for all studied elements show that Mn, Hf, U,Sc, K, V and Sr, with EFb10, are of natural origin, whereas Na, Ni, Co, Ba and Cr, with EFN10, are ofanthropogenic origin. Flat REE patterns with depletion in Th, V, Nb, Zr and enrichment in Al, Rb, Sr and Mnindicate that airborne dusts in Khuzestan come from the same source, which is likely an eroded sedimentaryenvironment outside Iran. In general, airborne dusts in Khuzestan are geochemically similar to airborne dustselsewhere in the world.

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1. Introduction

Dust storms have become a major environmental concern duringthe last decades in the oil- and gas-rich Khuzestan province insouthwestern Iran (Fig. 1). Dust storms frequently occur in Khuzestanmainly during summer, and intense dust storms are particularlyassociated with easterly-blowing winds (IRIMO Ahvaz, 2008). FromMarch 2007 to June 2009, an average of 60 dust storm days per yearhas occurred in various cities of Khuzestan province (Zarasvandi,2009). More than half of the number of dust storm days in 2007–2009hadmaximum visibility of b1 km (IRIMOAhvaz, 2008). Dust storms inKhuzestan likely emerge from sandy deserts, dried lakebeds, orchemically- and naturally-polluted regions in neighboring countries,are borne upwards and carried by winds to Iran (Zarasvandi, 2009).

For example, airborne dusts travel daily eastward from Saudi Arabianand Iraqi deserts to southwestern and southern Iran (Raespour, 2008).

The geological and geochemical characteristics of airborne dusts inseveral countries worldwide have been studied and documented (e.g.,Goldstein et al., 2008; Guerzoni et al., 1997; Hirose and Sugimura,1984; Hladil et al., 2008, 2010; Simonson, 1995; Talbot et al., 1986).However, there are no published studies about the geochemicalcharacteristics, geology and potential impact of airborne dusts onhuman health in Iran. In this paper, we give an overview of the spatio-temporal occurrences and geological–geochemical characteristics ofairborne dusts in Khuzestan. In addition, we explore with the limiteddata the possibility that occurrence of airborne dusts is associatedwith worsening prevalence of respiratory diseases in the province(Zarasvandi, 2009).

2. Study area

The province of Khuzestan, which occupies an area of 63,213 km2 insouthwestern Iran, has ca. 4 million inhabitants. It is located between

Fig. 1. Khuzestan province: (a) location and regional geological setting in Iran; (b) digital elevation model and locations of the studied stations.

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48°E and 49.5°E longitudes and between 31°N and 32°N latitudes(Fig. 1). Topographic elevations in the province vary between 0 and3740 m. The climate of the study area varies from arid to humid. Thenorthern parts of the province experience cold weather, whereas thesouthern parts experience tropical weather. Summer is from April toSeptember, whereas winter is from October to March. Annual mean ofmaximumsummer temperatures in the province is about 50 °C (in July)and minimum winter temperature is 9 °C (in March). The annualamounts of rainfall are 150–256 mm in the south and 995–1100 mm inthe north, and about 70% of annual rainfall events occur from Februaryto April. The annual evaporation is 2000–4000 mm. Predominant winddirections in the province are W→E and NW→SE (Fig. 2).

The study area is part of Zagros orogenic belt (Fig. 1), which is theproduct of three major geotectonic events associated with collision

between the Arabian and Iranian plates (Alavi, 2004). The Zagrosorogenic belt consists of three parallel tectonic zones from NE to SW:(1) the volcanic–plutonic zone (Urumieh-Dokhtar belt); (2) theSanandaj-Sirjan metamorphic zone; and (3) the Zagros fold belt(Alavi, 2004). Sedimentary rocks consisting of chemical–biochemicallimestones and clastic sandstones-conglomerates, with ages rangingfrom Cretaceous to Quaternary, occupy the central and northern partsof the Khuzestan province as mountains. Geomorphologically,Khuzestan province is located in a basin occupied by Cenozoic-quaternary alluvial sediments mostly derived from the chemical andmechanical erosion of the Zagros Mountains.

Rapid erosion in the Zagros area is accompanied by high water flowresulting in large stream load. Rock and mineral fragments aretransported by streams toward south of the province and are deposited

Fig. 2. Wind rose for the Khuzestan province in 1994–2008 (IRIMO, Ahvaz station,2008).

Fig. 3. High-volume air sampler model TCR (top) and PM10 cellulose sampler filter(bottom).

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on alluvial and sedimentary plains (e.g., Ahvaz city). Deposits ofsediments show diverse layers and mixtures of sand, silt and hardmud. The area of the province's capital city—Ahvaz—is characterized bythe predominance of alluvial and sedimentary rocks of both chemicaland detrital origins. The sand and much of the coarse silt fractions ofalluvial deposits are typically composed of quartz, whereas the fine siltand clay fractions are dominated by clays. Mineral fragments in thealluvial deposits are sorted by size due to differences in specific gravityand to some chemical dissolution during transport.

3. Approaches and methodology

3.1. Analysis of spatio-temporal occurrence of dust storms

Information about dust storms of regional source and coveragewere obtained from meteorological stations in Khuzestan province(Table 1). Data of dust storm days recorded from 1996 to 2009 at 10stations (Abadan, Ahvaz, Izeh, Behbahan, Bostan, Dezful, Ramhormoz,Shoushtar, Mahshahr and Masjed-e-Soleiman (or MIS)), out of the 14stations in the province, were considered in this study because thosein the other four stations have several daily/monthly gaps. Thealtitudes of the 10 stations vary from 6 m in Mahshahr to 767 m inIzeh (Zarasvandi, 2009). To analyze the spatio-temporal occurrence,we took the annual average of dust storm days during the 1996–2009

Table 1Number of dust storm days recorded from 1996 to 2009 in selected Khuzestan stations.

Station 1996 1997 1998 1999 2000 2001 2

Abadan 31 46 26 54 84 40Ahvaz 26 38 12 54 97 47Behbahan 9 12 8 13 62 6Bostan 23 14 6 38 82 22Dezful 73 105 50 76 112 46Izeh 12 22 1 29 64 11Mahshahr 11 30 7 35 76 20MIS 57 70 8 50 116 40Ramhormoz 16 18 0 27 72 9Shoushtar 20 20 7 36 53 10SUM 278 375 125 412 818 251 2MEAN 28 38 13 41 82 25

periods per station and then interpolated the average data by inversedistanceweighting (IDW)method.We also took the annual average ofsummer dust storm days and the annual average of winter dust stormdays during the 1996–2009 periods per station and then interpolatedthe separate average data by IDW method.

002 2003 2004 2005 2006 2007 2008 2009

39 84 49 79 52 39 139 5053 108 64 102 59 83 152 523 49 31 44 22 39 118 27

37 109 62 97 32 39 87 4558 124 94 117 51 60 141 4111 73 31 32 12 29 78 2427 49 36 61 17 33 96 2845 129 65 79 30 40 100 379 70 22 30 21 39 79 207 35 16 35 18 23 45 27

89 830 470 676 314 424 1035 34329 83 47 68 31 42 104 35

Fig. 4. Trend of annual average number of dust storm days in Khuzestan based on datain Table 1.

Fig. 5. Spatial distribution of annual average number of

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3.2. Analysis of mineralogy and morphology of airborne dusts

Traditionally, collecting storm dusts aims to determine totalsuspended particles (TSP). However, consideration of the U.S. Environ-ment Protection Agency particle size classes, such as PM2.5 and PM10, isnow essential in air pollution studies (Rodríguez et al., 2009). Thediameters of PM2.5 and PM10 particles are 2.5 μm and b15 μm,respectively. PM10 particles usually contain materials of natural origin,whereas PM2.5 particles contain materials of anthropogenic origin(Rodríguez et al., 2009). However, PM2.5 and PM10 particles can carrypollutants, especially chemical compounds with specific mineralogy andmorphology, and can be dangerous to human health.

In this study, airborne dust samples were collected to obtain TSP,PM2.5 and PM10 by using the high-volume air (HVA) sampler model

dust storm days in Khuzestan during 1996–2009.

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TCR (Fig. 2). The sampler was set about 2 m above the ground. Thevacuum pump of the sampler was powered by domestic electricity.The vacuum pumps were equipped with an automatic air mass flowmeter, calibrated with an accuracy of ±1.5%. The flow rate of the HVAsampler was set at an average of 20 l/min (under local air pressure).All dust samples were collected on TefloTM (Pall Corporation) filtercellulose with pore size of 1 μm (Fig. 3). The air volume for eachsample was calibrated to standard sea level pressure using theaverage pressure, which was automatically measured every 20 min ofeach sampling period.

The mineralogy of airborne dust samples was analyzed by XRD atthe Kansaran Binalood in Pardis Science and Technology Park (Iran).

Fig. 6. Spatial distribution of annual average number of sum

The mineralogy and morphology of airborne dusts samples wereanalyzed by SEM using the Leo 1455 VP device in the Shahid ChamranUniversity of Ahvaz (Iran).

3.3. Analysis of geochemical characteristics of airborne dusts

Analyses of the chemical and physical characteristics of storm-generated dusts are essential in studies on the environmental impactof dust storms (Zarasvandi, 2009). The chemical composition ofairborne dusts is necessary for clarifying the likely source of dustsand is important for quantitative climate modeling (Goudie andMiddleton, 2006). The chemical composition of airborne dusts is also

mer dust storm days in Khuzestan during 1996–2009.

Fig. 7. Spatial distribution of annual average number of winter dust storm days in Khuzestan during 1996–2009.

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important in understanding their possible effects on health, soils,precipitation, ocean biogeochemistry and weathering phenomena(Goudie and Middleton, 2006).

Table 2Khuzestan airborne dust samples collected in 2008 and 2009: minerals detected by XRD.

Sample Collection date Size Main compone

AH1-87 24/01/2009 PM10 Calcite, quartzAH2-87 24/05/2008 TSP CalciteAB1-87 24/05/2008 TSP CalciteAB2-87 23/02/2009 TSP CalciteHO1-87 26/09/2008 TSP CalciteAH3-87 12/02/2009 PM10 Calcite, quartzAH4-87 07/09/2008 TSP Calcite, quartzHO2-87 08/09/2009 TSP Calcite, quartzAH5-87 16/03/2009 PM10 Calcite, quartz

During dust storm days in 2008 in different stations in Khuzestan,we were able to collect nine samples of airborne dusts. Those sampleswere analyzed at the Kansaran Binalood Company in the Pardis

nt(s) Intermediate component(s) Minor component(s)

Muscovite, illite –

– –

– –

– GypsumQuartz, calcite, palygorskite –

Kaolinite, palygorskite –

– –

– –

Kaolinite, palygorskite –

Fig. 8. SEM images of airborne dust particles in Khuzestan: (a) calcite; (b) quartz; (c) calcite and clay aggregates; (d) gypsum. Scale bar in each image is 2 μmexcept in (b) where it is10 μm.

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Science and Technology park Laboratory (Tehran, Iran) for majoroxides and trace elements by XRF (Philips PW 2400, equipped with anRh-tube) using fused borate glass beads. To further study thegeochemistry of Khuzestan, additional storm dust samples were

Fig. 9. SEM images of pore openings in commonhealthmasks used in Khuzestan: (a) high-den

collected in 2009 for major and trace element determinations by ICP-MS analysis. Samples of dust PM2.5, PM10 and TSP collected by HVAsampler on Teflon TM filter cellulose were placed in special containersto avoid secondary contamination andwere sent to ACME laboratories

sitymask (scale bar is 100 μm); (b) drymask (scale bar is 20 μm); (c) and (d)wetmasks.

Table 3Khuzestan airborne dust samples collected in 2008: element compositions determined by XRF.

Sample AH1-87 AH2-87 AB1-87 AB2-87 HO1-87 AH3-87 AH4-87 HO2-87 AH5-87

Major elements (%)SiO2 42.2 36.7 6.8 32.9 44 42 40.6 41.8 54.1Al2O3 13.4 8.3 6.2 12.2 12.7 13.5 12 10.5 9.8Fe2O3 7.8 1.62 0.34 1.89 4.7 5.8 3.56 2.7 2.51CaO 20 10.4 1.62 10.4 18.6 21.2 14.7 12.1 13.3Na2O 3.8 21 4.2 21.3 5.1 2.1 12.1 14.5 10.4MgO 8.2 18.4 2.1 18.2 9.2 9.2 12 12.5 5.4K2O 2.27 1.3 28.6 1.6 2.08 2.24 1.89 1.8 2.13TiO2 0.93 0.58 0.067 0.46 0.75 0.84 0.62 0.53 0.48MnO 0.113 0.001 0.01 0.001 0.08 0.103 0.069 0.045 0.039P2O5 0.34 0.001 0.26 0.001 0.51 0.51 0.001 0.005 0.15

Trace elements (ppm)Ba 10 10 10 10 10 10 10 10 10Ce 10 10 10 10 10 10 10 10 10Co 10 10 10 10 10 10 10 10 10Cr 220 10 10 10 190 180 230 10 110Cu 150 10 10 930 10 100 10 10 10Nb 270 2400 630 2600 430 170 790 1100 180Ni 10 10 10 10 10 80 10 10 10Pb 10 10 10 10 10 10 10 10 10Rb 10 10 10 10 10 10 10 10 10Sr 1030 10 10 10 10 750 10 10 480W 10 10 10 10 10 10 10 10 10Y 160 10 10 10 10 80 10 10 100Zr 1000 10 10 10 10 590 10 10 590Zn 420 10 10 10 160 160 10 10 6600Mo 330 2900 1100 3100 550 260 1300 1700 260U 10 10 1600 10 10 10 10 10 10Th 10 10 10 10 10 10 10 10 10Cl 2200 7600 850 10 1800 3400 2100 6100 1000Br 10 10 491174 2000 10 10 10 10 10S 3600 10 10 10 18000 18800 17000 25000 7500

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in Vancouver for ICP-MS analysis. During 14 dust storms days fromApril 2009 to August 2009, 31 samples of TSP, PM10, and PM2.5 havebeen collected from Ahvaz and Abadan cities. In addition, five samplesof TSP were obtained from the Mahshahr, Shoushtar, MIS andKhorramshahr stations using a portable sampler.

Samples for ICP-MS analysis, each weighing 0.07 g, were digestedusing 65% pure HNO3 and 40% pure HF for 4 h at 150–190 °C. Samplesolutions were left to evaporate at 230 °C after adding 60% pure HClO4

(thus, resulting in acid ratios of HNO3:3HF:HClO4). Resulting residueswere dissolved by adding HNO3 and distilled water to obtain 25 ml of5% HNO3 sample solutions for ICP-MS analysis. Digestion of interna-tional reference materials (ash and soil standards), Teflon TM filtercellulose and acid blanks were prepared following the sameprocedure. Analytical errorswere estimated at b5% formajor elementsand about 10% for trace and rare earth elements. We noted that somenon-metallic crustal elements (such as Si, S and Cl) could not bemeasured due to the digestion procedure applied.

Estimates of enrichment factor (EF) aid in (a) differentiatingbetween element concentrations that originate from human activitiesand those from natural sources and in (b) assessing degree ofanthropogenic influence (Cong et al., 2007). The EF of an element x(EFx) in a material sample with respect to its natural abundance can beestimated as EFx=(Cx÷Cref)sample/(Cx÷Cref)crust, where Cx is concentra-tion of element of interest and Cref is concentration of reference element.According to this equation, EFx values close to 1 indicate elements ofcrustal origin whereas EFx valuesN1 indicate elements of non-crustal(including anthropogenic) origin. In this study, Al was used as areference element because it is abundant in the crustal materials, it isusually not of anthropogenic origin and, consequently, values of EFAl areclose to 1. Because various lithologies in source areas show elementcontents that are close to those of the upper continental crust (UCC)(Taylor and McLennan, 1995), elements with EFx of N10 are consideredto be of non-crustal (anthropogenic?) origin (Morata et al., 2007).

4. Results and discussion

4.1. Spatio-temporal occurrence of dust storms

The annual averages of number of dust storm days recorded at 10stations in the Khuzestan province during 1996–2009 (Table 1) showan increasing trend with about two additional dust storm days perannum (Fig. 4). The average number of dust storm days in 1998, 2001,2002, 2006, 2007 and 2009 is lower compared to average trend line(Fig. 4). This is likely due to high rainfall in the province during each ofthose years. The average number of dust storm days in 2000, 2003,2005 and 2008 is higher compared to average trend line (Fig. 4).This is likely due to low rainfall in the province during each of thoseyears.

Data recorded at the 10 Khuzestan stations during 1996–2009(Table 1) show an average of 47 dust storm days per year. The stationsin Dezful, Abadan, Ahvaz, MIS, and Bostan recorded above-averagenumber of yearly dust storm days, whereas the other stationsrecorded below-average number of yearly dust storm days (Fig. 5).Data recorded at the 10 Khuzestan stations during 1996–2009 showan average of 88 summer dust storm days per year. The stations inDezful, MIS, Ahvaz, and Abadan recorded above-average number ofsummer dust storm days, whereas the other stations recorded below-average number of summer dust storm days (Fig. 6). Data recorded atthe 10 Khuzestan stations during 1996–2009 show an average of 27winter dust storm days per year. The stations in Dezful, Ahvaz,Abadan, Bostan and MIS recorded above-average number of winterdust storm days, whereas the other stations recorded below-averagenumber of winter dust storm days (Fig. 7).

The 1996–2009 data of dust storm days, in both summer andwinter, indicate that the western sector of the province experiencedmore dust storm days than the eastern sector (Figs. 5–7). The 1996–2009 data of dust storm days indicate also that the northern sector of

Table 4Khuzestan airborne dust samples collected in 2009: major and trace element compositions (in ppm) determined by ICP-MS analysis. PM=particulate matter. TSP=total suspendedparticles.

Sample AH-1 AH-4 AH-5 AH-6 AH-7 AH-8 AH-9 AH-10 AH-12 AH-13 AH-15 AH-16

PM TSP PM10 TSP PM2.5 PM2.5 PM-10 PM-10 TSP PM2.5 TSP PM-10 TSP

Al 3100 4700 5700 2400 4500 2800 3500 2800 700 4400 2400 4200Fe 2400 4400 7000 500 300 1200 2800 3800 900 5000 3800 7100Ca 11,300 17,000 26,900 4400 500 6300 11,600 13,900 2400 20,600 11,700 22,100Mg 2200 4000 4700 1000 1500 1400 2700 3100 600 3900 2500 4500Na 6640 4840 410 8120 13,920 7450 6730 630 600 670 800 830K 2600 1900 1600 2100 3000 2000 2200 1600 500 1400 1400 1900Mn 53 116 162 16 20 28 67 87 20 120 86 138Mo 0.42 0.53 0.32 0.33 0.34 0.23 0.39 0.34 0.29 0.28 0.31 0.38Cu 8.14 9.25 8.84 4.29 5.94 34.58 7.96 11.54 6.48 8 8.87 9.77Zn 2078 1089.3 23 2673.9 4926.9 2451 1756.6 18 19.3 37.1 29.2 43.8Ni 8.5 25.6 30 2.8 2 4.6 14.7 21.1 3.8 20.8 11.2 17.9Co 1.3 3.7 4.6 0.3 0.2 0.9 2.4 2.6 0.6 3.4 1.9 3.3As 0.9 1.8 2.5 0.2 0.2 0.8 1.2 1.0 0.2 1.4 0.8 1.8U 0.2 0.2 0.3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2Th 0.3 0.6 1.1 0.2 0.2 0.2 0.4 0.4 0.2 0.7 0.5 0.8Sr 50 57 71 30 46 38 48 46 9 65 38 65Cd 0.61 0.49 0.2 0.94 2.71 0.8 0.68 0.21 0.27 0.29 0.13 0.28V 6 9 15 4 4 4 7 8 4 11 9 15Ca 11,300 17,000 26,900 4400 500 6300 11,600 13,900 2400 20,600 11,700 22,100P 90 160 240 30 20 40 90 120 240 170 300 220La 1 3 4 1 1 1 2 2 1 3 2 3Cr 9 20 23 5 3 5 11 14 6 17 10 17Ba 2860 1446 54 3899 7265 3589 2458 32 8 42 19 42Ti 60 110 150 20 20 30 70 80 20 120 70 120B 1925 1218 40 2000 2000 2000 2000 40 40 40 40 40Na 6640 4840 410 8120 13,920 7450 6730 630 600 670 800 830Sc 0.7 1.1 1.6 0.2 0.2 0.2 0.6 0.8 0.4 1.4 0.7 1.1Tl 0.25 0.07 0.06 0.08 0.08 0.04 0.18 0.26 0.06 0.06 0.18 0.22

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the province experienced more dust storm days than the southernsector.

4.2. Mineralogy and morphology of airborne dusts

Based on XRD analysis, samples of airborne dusts collected atmentioned stations (Abadan andAhvaz cities) are composed ofmostlyof three mineral groups: carbonates (mainly calcite), silica (mainlyquartz) and phyllosilicates (mainly kaolinite) (Table 2). However, thePM10 fraction usually has higher calcite and quartz content comparedto the TSP and PM2.5 fractions. The abundance of calcite and quartz inmost of the samples indicates detrital sedimentary origin for naturalparticles in airborne dusts in Khuzestan (Zarasvandi, 2009). Thesamples are characterized by multi-modal particle-size distributionsand are comprised predominantly of angular to sub-rounded quartzparticles. These can be the result of various types of dust concentra-tions during the storms in the study area, variable source sedimentaryrocks and silt-size particles, and particle-size redistribution (Hladilet al., 2008). The low reactivity of quartz with heavy metals suggeststhat its presence is not a factor in concentrating heavy metals inairborne dusts.

Several SEM images, taken with different magnifications ofselected samples, show that spherical, irregular, long and prismatic,crystalline and rhombic twinning shapes are the most commonshapes of dusts in the samples (Fig. 8). The SEM studies indicate thatPM10 is the most frequent particulate size of Khuzestan airbornedusts. Spherical particles of b5 μm in PM2.5 are mainly clayaggregates (phyllosilicates), whereas large prismatic crystals of 20–40 μm are gypsum (sulfate). Regular crystals of 10–20 μm in PM10samples are mainly calcite, whereas semi-spherical or irregularshapes of 10–20 μm in PM10 are quartz. SEM measurements indicatethat the sizes of storm-generated dusts in Khuzestan vary between 20and 50 μm.

The mineralogy and morphology of airborne dusts are controlledby regional geology and wind direction (Zarasvandi, 2009). PM10particles have been reported in deserts neighboring the study area.Comparison of the mineralogy of the airborne dust samples with thegeology of western Khuzestan and central to eastern Iraq suggeststhat desert sands in these areas are likely themain sources of calcite inairborne dusts in the study area (Raespour, 2008). Engelbrecht et al.(2009b) have shown that samples of airborne dusts derived frompoorly drained rivers, lakes and basins in central and southern Iraqcontain substantial calcite (33–48%), quartz, and feldspar with minorchlorite and clay minerals. In addition, Crouvi et al. (2010) indicatethat consistencies between mineralogical compositions of loess andupwind sand dunes and temporal associations between sand duneactivity and loess deposition suggest that sand dunes were importantsources of coarse silt grains comprising themajority of adjacent desertloess. Based on these studies, it is likely that central and southernparts of Iraq and western parts of the Khuzestan province, which arecovered by sand dunes, are sources of coarse dust grains in the studyarea. Due to lack of minerals indicative of igneous and metamorphicenvironments, the mineralogy of the studied samples suggests thatthe likely main sources of dusts in Khuzestan are sedimentary basinsespecially those in Iraq and Saudi Arabia (Zarasvandi, 2009).

To relate information about airborne dust particle size andconstituent minerals with common health masks used in theKhuzestan province, we evaluated the performance of two types ofmasks to filter environmental dust. Specifically, we investigated thefiltering capacity of the masks for various particle sizes and mineralsthrough SEM analyses. Common healthmasks used in Khuzestan havepores of 5–40 μm (Fig. 9). Thus, masks with pores of N20 μm do nothave the ability to block airborne dusts. However, about 90% ofvarious particles in Khuzestan dusts can be blocked when the masksare wet. Wet masks with pores of b20 μm are sufficient for usageagainst clay minerals in PM2.5 particles. Large and radial gypsum inPM10 stay on most wet masks with various pore sizes.

Table 4 (continued)

AH-18 AH-19 AH-21 AH-22 AH-24 AH-25 AH-26 AH-28 AH-29 AH-30 AB-1-88 AB-2-88 AB-3-88

PM10 TSP PM-10 TSP PM2.5 PM2.5 PM-10 TSP PM-10 TSP TSP PM2.5 TSP

5000 10,200 1200 3400 1900 2700 4400 6500 4400 10,100 9000 400 30005500 12,300 1400 400 800 1100 5400 7300 5400 12,000 9500 500 3800

19,600 46,100 4100 16,200 4300 5900 22,500 33,600 20,900 47,500 38,000 1800 12,6004600 9200 1000 3200 1100 1400 3800 5700 3600 8300 8100 400 2900570 350 620 280 6270 7590 490 420 540 360 2420 470 320

1300 2000 800 1100 1800 2400 1200 1600 1300 2400 2300 200 700143 308 31 104 19 26 124 191 128 283 258 12 88

0.3 0.39 0.17 0.19 0.27 0.32 0.4 0.37 0.48 0.43 0.48 0.09 0.279.65 16.16 6.79 9.71 8.07 8.21 7.21 11.74 7.56 15.58 17.37 2.35 7.3

18 32.6 9.7 16.3 1967.8 2528.4 19.3 27.2 15.9 32.9 437.2 2.5 20.332.8 69.2 7.8 22.1 6.1 6.4 26 39.4 26.9 61.5 62.4 2.8 15.64 8.8 1.1 3 0.3 0.6 4.1 6.2 3.9 8.9 8.6 0.2 2.71.4 3.8 0.3 1.6 0.4 0.5 1.7 2.5 2.1 4.1 3.4 0.2 1.40.2 0.3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.2 0.20.7 1.5 0.2 0.6 0.2 0.2 0.8 1 0.8 1.6 1.3 0.2 0.5

52 108 12 49 27 36 66 105 61 130 110 5 450.11 0.17 0.03 0.17 0.63 0.75 0.1 0.19 0.1 0.16 0.23 0.02 0.04

11 25 4 8 4 6 12 16 12 25 19 4 919,600 46,100 4100 16,200 4300 5900 22,500 33,600 20,900 47,500 38,000 1800 12,600

360 330 260 150 20 40 350 300 310 350 310 230 1203 7 1 2 1 1 3 5 3 7 6 1 3

22 44 6 15 5 7 18 26 19 41 40 4 1135 80 11 34 2165 2689 38 64 35 78 546 5 42

110 200 30 80 20 30 100 150 110 200 190 20 9040 40 40 40 1919 2000 40 40 40 40 311 40 40

570 350 620 280 6270 7590 490 420 540 360 2420 470 3201.4 2.5 0.7 1.2 0.3 0.4 1.5 1.5 1.2 2.5 1.8 0.6 1.10.09 0.07 0.12 0.11 0.08 0.15 0.05 0.07 0.05 0.08 0.08 0.04 0.04

Table 5Selected Khuzestan airborne dust samples collected in 2009: Ti, Nb, Ga, Al, Rb and Kcontents (in ppm, except for Al and K) determined by ICP-MS analysis, and Ti/Nb, Ga/Aland Rb/K ratios.

Sample Ti Nb Ti/Nb Ga Al (%) Ga/Al Rb K (%) Rb/K

AH-1 60 0.37 162.2 1.9 6.5 0.29 6.6 2.6 2.54AH-5 150 0.42 357.1 1.5 5.7 0.26 5.3 1.6 3.31AH-10 80 0.20 400.0 0.7 2.8 0.25 9.6 1.6 6.00AH-13 120 0.26 461.5 1.3 4.4 0.30 5.0 1.4 3.57AH-16 120 0.34 352.9 1.5 4.2 0.36 9.0 1.9 4.74AH-19 200 0.46 434.8 2.5 10.2 0.25 8.3 2.0 4.15AH-22 80 0.18 444.4 0.8 3.4 0.24 4.8 1.1 4.36AH-28 150 0.37 405.4 1.9 6.5 0.29 6.6 1.6 4.13AH-30 200 0.55 363.6 2.8 10.1 0.28 8.5 2.4 3.54

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4.3. Geochemical characteristics of airborne dusts

4.3.1. Major oxidesRecently, geochemical evidence frommajor and rare earth elements

and Pb isotopes, have proved that airborne dusts have regionalvariations in material compositions and sources. Research on presentairborne dust deposition events contributes to understanding ofbackground sedimentation record and key aspects of source rocks(Hladil et al., 2008, 2010). The main chemical components of airbornedusts (and their average contents) in many dust storm areas in theNorthern Hemisphere are SiO2 (59.99%), Al2O3 (14.13%), Fe2O3 (6.85%),CaO (3.94%), MgO (2.60%) and K2O (2.35%) plus water and organicmaterials (Goudie and Middleton, 2006). One of the most importantfactors that influence the concentration and chemical composition ofdusts is mineralogy of source materials.

The dominant major oxides in Khuzestan airborne dusts are SiO2

and Al2O3 (Tables 3 and 4). The concentrations of these two majorelements are similar to those of normal airborne dusts worldwide. Theabundance of SiO2 in Khuzestan airborne dusts is mainly due toquartz. The average concentration of SiO2 in Khuzestan airborne dustsis less than the average value presented by Wu et al. (2009) for dustaerosols over the Eastern Pamirs. Major oxides in Khuzestan airbornedusts are more concentrated in coarse particles than in fine particles(TSPNPM10NPM2.5). The likely reason for this is transportation ofminerals and altered indiscrete particles.

Nearly constant Ti/Nb ratios indicate a similar provenance forsiliclastic rocks (Engelbrecht et al., 2009b). Table 5 shows all but oneof the studied dust samples have Ti/Nb ratios of ~400 (excludingsample AH-1, mean=402.5 and standard deviation=41.9). Thus,most Khuzestan airborne dusts likely originate from essentially thesame source area (cf. Zarasvandi et al., in press). Well mixing of dustsby winds is also a likely reason for the narrow variance of Ti/Nb ratiosin Khuzestan airborne dust (cf. Crouvi et al., 2010). In addition,because Rb commonly substitutes for K and because Ga commonly

substitutes for Al in aluminosilicates, nearly constant ratios of eitherRb/K or Ga/Al in airborne dusts indicate homogeneity of aluminosil-icates in source areas of dusts (Engelbrecht et al., 2009b). Table 5shows that, because the studied dust samples have nearly constantGa/Al ratios of ~0.28 (mean=0.28 and standard deviation=0.04)and nearly constant Rb/K ratios of ~4 (mean=4.04 and standarddeviation=0.98), aluminosilicates in the source areas of Khuzestanairborne dusts are roughly homogeneous.

Ratios of Si/Al in TSP and PM10 of dust samples are similar,probably due to the presence of silicate, tectosilicate, and alumino-silicate minerals in most size fractions of Khuzestan airborne dusts.Some element ratios (e.g., Mg/Al, Ca/Al, and Fe/Al) in airborne dusts(Table 6) indicate contribution of clays to the chemical compositionsof Khuzestan airborne dusts. These geochemical characteristics aregenerally common to the TSP, PM10 and PM2.5 fractions of Khuzestanairborne dusts (Zarasvandi, 2009), suggesting that source materials ofthose dusts are similar, if not the same.

The chemical compositions of airborne dust samples in Khuzestanare similar to those in other parts of the world (Zarasvandi, 2009;

Table 6Major element ratios in selected samples of Khuzestan airborne dust particles and somestorm-dust particles in theworld. N=number of samples. UCC=upper continental crust.

Site N Mg/Al Ca/Al Ti/Al Fe/Al Analysis Reference

Khuzestan dustTSP samples – 0.90 4.6 0.02 1.10 ICP-MS This paperPM10 samples – 0.82 3.9 0.02 1.05 ICP-MS This paperPM2.5 samples – 0.61 2.4 0.01 0.60 ICP-MS This paperTotal 26 0.84 3.9 2.02 0.97 ICP-MS This paperUCC – 0.16 0.37 0.04 0.44 Taylor and

McLennan(1995)

Aerosol at other sitesTashkurgan 1 – 2.63 0.09 1.14 PIXE Makra et al.

(2002)Kara Kul 1 – 1.63 0.07 1.03 PIXE Makra et al.

(2002)Shaartuz – – 0.084 – 0.4 XRF Gomes and

Gillette(1993)

Aksu 18 0.5 2.04 0.09 1.04 PIXE Zhang et al.(2003)

Tien ShanObservatory

9 – 2.17 0.11 1.07 XRF Hoornaertet al. (2004)

Inilchek firn coreHigh dustsample

13 – 6.10 – 0.42 ICP-MS Kreutz andSholkovitz(2000)

Mid dustsample

19 – 5.15 – 0.48 ICP-MS Kreutz andSholkovitz(2000)

Low dustsample

66 – 6.88 – 0.53 ICP-MS Kreutz andSholkovitz(2000)

Fig. 10. Khuzestan airborne dust samples: REE concentrations normalized to (a) CI (orcarbonaceous) chondrites (Anders and Grevesse, 1989) and (b) upper continental crust(Taylor and McLennan, 1995).

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Table 6). Comparisons Fe/Al ratios in samples of airborne dusts inKhuzestan with those in other parts of the world indicate that thisratio is almost invariant and, thus, can be good source tracer for dustorigin (Table 6). The Fe/Al ratio is not expected to change duringtransport, but its variations are mostly due to variations in claymineral compositions (Goudie and Middleton, 2006). Ratios of Ca/Alshow greater variations in TSP, PM10, and PM2.5 of Khuzestanairborne dusts. The Ca/Al ratios in all Khuzestan dust samples arerelatively high, probably because the samples were all collectedduring summer or warm periods. Rainfall during summer facilitatesseparation of Ca-bearing compounds and, thus, concentration of saltsin source deserts and enrichment of Ca in dusts (Wu et al., 2009).

4.3.2. Rare earth elements (REEs)Analysis of REEs is very important for investigation of sediments

sources (Liu et al., 1993; Taylor and McLennan, 1995). However,distribution patterns of REEs are not suitable for identifying sources ofatmospheric dusts because they are typical of the UCC (Wu et al.,2009). Nevertheless, plots of Ce/Yb, Eu/Yb, LREE/HREE, ∂Eu=(EuN/(SmN*GdN)1/2), ∂Ce=(CeN/(LaN*PrN)1/2) can aid in analysis ofemission areas of dusts (Sun, 2002). The REE compositions of theKhuzestan airborne dust samples, normalized to CI (or carbonaceous)chondrites (Anders and Grevesse, 1989), show similar patterns withsteep LREE profiles (LaN/SmN=3.3–3.57) and relatively flat HREEprofiles (GdN/YbN)=0.23–0.24) (Fig. 10a). In addition, all of theKhuzestan airborne dust samples have similar LREE/HREE ratios andshow depletion in LaN/YbN ratios (Fig. 10). The overall patterns ofREEs in the Khuzestan airborne dust samples are uniform and aresimilar to the patterns of average UCC values (Fig. 10b). Enrichment ofLREE rather than HREE (Fig. 10a) indicates the presence of detritalsediments.

One factor that can affect compositions of dusts is size of particles.For example, enrichment of LREE rather than HREE suggests increasedpercentage of clay rather than sand in source bedrocks. That isbecause, with minimum threshold wind speed, clay- to silt-sizeparticles (b63 μm) can be lofted into the air but not sand-size particles(N63 μm). Thus, the variations in concentrations of REEs in theKhuzestan airborne dust samples are likely due to variations in sourcematerials from loess to sand (cf. Yang et al., 2007). This hypothesis issupported by observations that total REEs are lower in sand andsandstone of post-Archean age than in shale (Taylor and McLennan,1995) and clay minerals are potential major carriers of REEs in shale(Condie, 1991).

The Eu anomalies are similar in the various size fractions ofKhuzestan airborne dust samples. However, the generally lowconcentrations of REEs in coarse samples are likely associated withmineralogy, probably a larger relative abundance of REE-poorminerals like quartz and feldspars (cf. Yang et al., 2007). Carbonate-and salt-rich sediments show depletion in REEs (Liu et al., 1993). Therelatively large amount of feldspar and epidote is most likelyresponsible for the enrichment of Eu (Yang et al., 2007).

Ratios of REEs and trace elements are used to define properties ofairbornedusts and for tracing their source (Ding et al., 1999;Gallet et al.,1996). REEs and Th in superficial processes have similar behavior and anaverage La/Th ratio of 2.8 in fine-grained sediments gives anindependent estimate of UCC composition (Taylor and McLennan,1995). The average La/Th ratio in Khuzestan airborne dust samples is 3.The variations in U/Pb versus Th/Pb ratios are also widely used to tracethe origin of dusts (Wu et al., 2009). Th and U are known to havedifferent geochemical behaviors in certain surficial process. Th is largelyinsoluble, while the redox-dependent mobility of U is associated withalteration material (Wu et al., 2009). The Khuzestan airborne dustsamples show similar Th/U ratios (ranging from 0.25 to 4, with anaverage of 2.1). The low concentrations of dust samples in TSP, PM10,and PM2.5 size fractions show much scatter in La/Th and Th/U ratios(Fig. 11). However, the plots of LREE/HREE versus δEu, LaN/SmN versusGdN/YbN, NdN/YbN versus δCe and Th/U versus La/Th ratios are similar indifferent size fractions of Khuzestan airborne dusts (Fig. 12).

Fig. 11. Khuzestan airborne dust samples: plots of Al concentrations (ppm) versus (a)La/Th (a) and (b) Th/U.

149A. Zarasvandi et al. / Journal of Geochemical Exploration 111 (2011) 138–151

4.3.3. Element enrichment factorIn the different size fractions of Khuzestan airborne dusts, Hf, Sc, K,

La, V, Sr, U, Mn and Fe have EF values of b10, which suggest that theseelements are predominantly derived from crustal sources (e.g.,sediments). In contrast, Ba, Ni, Cr and Zn (and to a lesser extent Naand Co) have EF values of N10, suggesting that these elements arederived from non-crustal (anthropogenic?) sources. It is likely thathigh concentrations of Ba, Ni, V and Co in the Khuzestan airbornedusts are derived from fossil fuel combustion, traffic emission andupstream petroleum industry in Khuzestan or from airborne dustsource areas in neighboring countries (Iraq and Saudi Arabia). It isnoted (although not shown in Fig. 13) that EF for Zn is higher than S inthe PM2.5 and PM10 fractions of Khuzestan airborne dusts, suggestingpartition of element concentration due to particle size and origin.

Fig. 12. Khuzestan airborne dust sampl

4.3.4. Heavy metalsHeavy metals in airborne dusts are usually associated with

aluminosilicates particular clays and to some extent are associatedwith specific particle sizes in certain airborne dusts worldwide(Crouvi et al., 2010). For example, Cu concentrations usually havepositive correlations with particle sizes of materials, whereas Moconcentration usually lack either positive or negative correlationswith particle sizes of material due to its being immobile duringweathering and transformation process (Taylor andMcLennan, 1995).

In this study, it was found that Zn concentrations are higher inPM2.5 than in TSP or PM10 of Khuzestan airborne dust samples.Likewise, PM2.5 samples have a mean concentration of 0.44 ppm Agwhereas PM10 and TSP samples have mean Ag concentrations of0.24 ppm and 0.13 ppm, respectively. The likely reason for theseobservations is that Zn or Ag is commonly adsorbed by clays or istrapped in the crystal structures of tectosilicates. In contrast, TSPsamples have a mean concentration of 33 ppm Ni whereas PM2.5 andPM10 samples have mean Ni concentrations of 4 ppm and 18.7 ppm,respectively. In addition, the EF of Ni is highest in TSP samples.Likewise, TSP samples have a mean concentration of 168 ppm Mnwhereas PM2.5 and PM10 samples have mean Mn concentrations of2.4 ppm and 90 ppm, respectively. In addition, the EF of Mn is 4 in TSPsamples. The likely reason for these observations is that Ni or Mn iscommonly associated with organic matter, such as those derived fromupstream petroleum industry in Khuzestan or in airborne dust sourceareas in neighboring countries (Iraq and Saudi Arabia).

The concentration of Fe is not uniform in different particle sizes.The highest value of Fe is in PM2.5 and the lowest value in TSPsamples. In addition, U concentration in PM2.5 is 0.2 ppm, and inPM10 and TSP samples is 0.19 and 0.1 respectively. Thoriumconcentration is highest in TSP samples. The highest concentrationof Sr is in PM2.5 samples. The EF of Sr is 3.62 and 3.26 in TSP and PM2.5samples, respectively. Concentrations of Pb, Cd and rare elements arehigher in PM2.5 than in PM10 and TSP samples. TSP samples have amean concentration of 4.4 ppm V whereas PM2.5 and PM10 sampleshave mean V concentrations of 14.5 ppm and 8.6 ppm, respectively.The EF of V is similar in all particles size and it could originate frompetroleum industries in the region.

Calciumhas the highest concentration in PM2.5 samples and has thehighestEF. Themain reasonsof this enrichment are commonassociationof Ca with evaporate lakes and lands in the region (Engelbrecht et al.,2009a). In addition, the EF of Cr is N10 in the samples. Moreover, TSPsamples have a mean concentration of 8 ppm Cr whereas PM2.5 and

es: plots of various element ratios.

Fig. 13. Khuzestan airborne dust samples: values of element enrichment factor (EF) in different particles.

150 A. Zarasvandi et al. / Journal of Geochemical Exploration 111 (2011) 138–151

PM10 samples have mean Cr concentrations of 9.7 ppm and 10 ppm,respectively. These indicate an anthropogenic source for Cr. Bariumshows the highest EF of 134 in the samples. The main reason for thisfeature is that Ba is commonly associated with oil and gas drillingprograms in Khuzestan or in airborne dust source areas in neighboringcountries (Iraq and Saudi Arabia; Engelbrecht et al., 2009a).

5. Conclusions

The main findings of this study are as follows.

▪ In Khuzestan (southwestern Iran), during the period 1996–2009,there was (a) an average of 47 dust storm days per year, (b) alowest annual average of 13 dust storm days in 1998, (c) a highestannual average of 104 dust storm days in 2008, and (d) an averageincrease of two dust storm days per year. The cities where above-average number of dust storm days usually occurred are Dezful,Ahvaz, Masjed-e-Soleiman, Abadan and Bostan, whereas the citieswhere below-average number of dust storm days usually occurredare Mahshahr, Ramhormoz, Behbahan, Shoushtar and Izeh.

▪ Themajor sources of airborne dusts in Khuzestan are dry lakebeds,alluvial deposits and deserts in neighboring countries to the west.

▪ XRD analyses show that minerals present in airborne dusts inKhuzestan can be divided into three groups: (1) carbonates(mainly calcite); (2) silica (mainly quartz); and (3) clays (mainlykaolinite). Gypsum is a significant minor mineral component ofKhuzestan airborne dusts. SEM studies show that Khuzestanairborne dusts (a) have various shapes depending on mineralcomposition and (b) vary in size from 2 to 44 μm regardless oftheir mineral composition.

▪ XRF and ICP-MS analyses show that chemical composition ofKhuzestan storm-generated dusts is similar to some other airbornedusts in the world. The significant major oxides in Khuzestanairborne dusts are SiO2, Al2O3, Fe2O3, CaO andMgO. The overall flatpatterns of REEs in Khuzestan airborne dusts are associated withdepletion in Th, V, Nb and Zr and enrichment in Al, Rb, Sr and Mn,indicating that these elementswere derived from similar, if not thesame, sources. Enrichment factors of b10 for Mn, Hf, U, Sc, K, V andSr indicate that these elements were derived from natural (orgeological) sources. Enrichment factors of N10 for Na, Ni, Co, Baand Cr indicate that these elements were derived from anthropo-genic sources.

▪ Pores of common health masks used in Khuzestan vary between 5and 40 μm. Thus, maskswith N20 μmpores inadequately block fineairborne dusts, except when they are wet. This suggests thatairborne dusts are likely implicated in respiratory-related diseasesin Khuzestan.

Acknowledgments

We thank Jindrich Hladil, Steve Forman, and two anonymousreviewers for their critical comments, which significantly helped us toimprove our paper. This researchwasmade possible by the help of theoffice of vice-chancellor for Research and Technology, ShahidChamran University of Ahvaz. We acknowledge their support andare grateful for the funds provided by a research grant in 2010.

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