**13. Trace elements**

190 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

originating from local and well-defined sources.

CaO and MgO.

in SiO2, Al2O3, K2O and total Fe and significantly enriched in CaO, Na2O and MgO. The MgO is largely contained in dolomite and, to a lesser extent, in clay minerals such as palygorskite and montmorillonite [78, 44]. These components can be ascribed to the importance of evaporate minerals such as calcite, dolomite, halite and gypsum (as also suggested by the mineralogical analysis) inferred to have come from the desiccation taking place in the Hamoun dust source region. Furthermore, the elevated values for the trace elements Cl, F and S (Table 5) support the latter postulate as it would be expected from an evaporate-rich source for deflation of dust [e.g.,110]. Similar to the elemental composition of dust over Sistan, [44] determined a high fraction of SiO2 in silt, less CaO in calcite and slightly more Al2O3 in clay minerals at the Khowst site. At both Afghanistan sites (Bagram and Khowst), the SiO2 was dominant with fractions of about 50-55%, followed by Al2O3,

By comparing the major elements of different dust storms, some interesting relationships have been found. More specifically, on days (e.g. 15/11/2009, 7/1/2010, 23/1/2010) (Fig. 20a) when airborne dust was relatively depleted in SiO2, enhanced MgO and, particularly, Na2O values were recorded. Conversely, when SiO2 values were higher (e.g. 8/7/2010, 23/8/2010), both MgO and Na2O contributions dropped. This suggests that certain intense dust storms were richer in evaporate source material (i.e., elevated MgO and Na2O) coming from Hamoun dried lake beds, while others had more silica, reflecting weathered rock detritus from the Hirmand river and Afghanistan mountains. An explanation of these variable chemical compositions of dust samples is a real challenge, but it is postulated here that they may reflect local desiccation cycles and, possibly, even micro-climatic changes in the Hamoun-lakes dust source region. Excessive desiccation of the lakes would enhance potential evaporate minerals for deflation in drier periods, while in wetter periods, airborne dust would logically have been derived more from weathered fluvial detritus rich in SiO2.

Figure 21 summarizes the results of the elemental compositions determined by XRF analysis at both stations. For comparison reasons, the mean elemental composition found for several sites in southwestern Iran (Khuzestan province) [71-72] is also shown. The vertical bars express one standard deviation from the mean. Concerning the major elemental oxides over Sistan, both stations exhibit similar results, well within the standard deviations, suggesting that the transported dust over Sistan is locally or regionally produced with similarity in source region. In contrast, the mean elemental composition of airborne dust over Khuzestan province exhibits remarkable differences from that over Sistan, revealing various source regions and dust mineralogy. More specifically, the SiO2 percentage is significantly lower and highly variable over Khuzestan, which is also characterized by higher contributions of Na2O, MgO and K2O compared to Sistan. The dust storms over southwestern Iran may originate from local sources as well as being transported over medium- and long-ranges from different sources located in Iraq as well as in the Arabian Peninsula. A comparative study of the mineralogy and elemental composition of airborne dust at several locations in Iraq, Kuwait and the Arabian Peninsula [44] has shown significantly variable contributions, suggesting differences in overall geology, lithology and mineralogy of these regions. In further contrast, airborne dust over Sistan seems to have its individual characteristics

The average concentrations of trace elements (in ppm) in dust samples collected during major dust storms at stations A and B are summarized in Table 5, as obtained from XRF analysis. The results show that the dominant trace elements over Sistan are F and Cl, with the former being dominant in the vast majority of the dust events at station A. However, on two days (8/7/2010 and 23/8/2010) the Cl concentrations were extremely large, thus controlling the average value; there is a lack of observations at station B on 23/8/2010, thus the lower average Cl concentration. Note that on both these days, the SiO2 component is large, while MgO and Na2O are low (Fig. 20a). The dominance of chlorine indicates soil salinization in the Hamoun basin and along the Hirmand river and its tributaries. Furthermore, S exhibits higher concentration at station A, while for the other elements the concentrations between the two stations are more or less similar. The concentrations of potentially harmful and toxic elements, like Cs, Pb and As are, in general, low at both stations; however, Ba, Cr and Zn present moderate concentrations.

On the other hand, the analysis of the major element ratios provides essential knowledge of the dust chemical composition and source region. The ratios of Si/Al at stations A and B are

similar (7.8±0.8 and 8.3±0.9, respectively), due to the presence of silicate and aluminosilicate minerals in most dust samples. The ratios of Mg/Al (0.90±0.16, 0.92±0.12), Ca/Al (3.09±0.19, 3.12±0.19) and Fe/Al (0.51±0.02, 0.49±0.01) at the two stations suggest contributions of clays and Ca-rich (calcite) minerals to the chemical compositions of the airborne dust. In contrast, the Fe/Al ratio is low over Sistan and is nearly half of that found for airborne dust over southwestern Iran and several locations over the globe [72], but is comparable to that found over central Asia [111]. It should be noted that this ratio remains nearly invariant, ranging from 0.47 to 0.54, for all the collected dust samples at both stations and can be a good surrogate for the dust source region, since any variation in Fe/Al mainly corresponds to variations in clay minerals and not to coating during dust transportation [50]. In contrast, the Ca/Al ratio exhibits the highest variations from sample to sample (2.80-3.46), since it is influenced by particle size, with higher values as particle-size increases [72]. Synoptically, all the ratio values and the low standard deviations suggest similarity in geochemical characteristics over Sistan and a uniform source of airborne dust.

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 193

drains the Hilmand river, thus constituting a wetland area known as Hamoun. Hamoun lakes complex have an area about 4500 Km2 with water volumes of 13025 million m3 and play the role of a "water cooler" for the region when they are full of water as the severe

Severe droughts over the past decades, especially after 1999, have caused desiccation of the Hamoun lakes, leaving a fine layer of sediment that is easily lifted by the wind and therefore making the basin one of the most active sources of dust in south-west Asia [56, 50]. The strong "Levar", especially during the summer season, blows fine sands off the exposed lake bed and deposits this detritus within huge dune bed forms that may cover a hundred or more villages along the former lakeshore. As a consequence, the wildlife around the lake has been negatively impacted and fisheries have been brought to a halt, which also implies an impact on society. The drainage of the Hamoun wetlands, in association with the intense Levar winds in summer, is the main factor responsible for the frequent and massive dust storms over the Sistan region. Analysis of water surface in combination with dust storms showed that the Hamoun dried beds, particularly Hamoun Saberi and Baringak, have a

Systematic PM concentrations were measured in Zabol city, affected by the Sistan dust storms, covering the period September 2010 to August 2011. The results show that the PM10 concentrations were considerably higher than the corresponding European Union air quality annual standard. The analysis of the daily PM concentrations showed that the air quality is affected by dust storms from the Sistan desert, which may be very intense during summer. Hamoun, as an intense dust source region, caused a dramatic increase in PM10 concentrations and a deterioration of air quality (65% of the days were considered

Dust loading from the Hamoun basin appears to have a significant contributing influence on the development of extreme dust storms, especially during the summer days. This influence firstly seems to depend on the intensity and duration of dust storms, and secondly, on the distance from the source region, the wind speed and altitude. The grain-size distribution of the dust loading was strongly influenced by the distance from the dust source, since grain sizes shifted to larger values towards station B that is closer to the Hamoun basin. Furthermore, the particle size distribution exhibited a shift towards lower values as the altitude increases, with this feature seen to be more obvious amongst larger size particles, while the frequency of particles below 2.5 μm seemed not to be affected by altitude. In general, the regional dust loading and characteristics are subject to significant spatiotemporal variability. This finding necessitates more systematic observations at as many locations as possible around the Hamoun basin in order to improve the understanding of forcing dynamics, transport mechanisms as well as to quantify the dust amounts emitted

To fully understand mineral dust characteristics and the potential impact on human health, dust mineralogy and geochemical properties were examined in the Sistan region by collecting airborne samples at two stations and soil samples from several locations over

winds blow across the lakes.

from the Hamoun basin.

dramatic effect on dust storms as sources of aerosols.

unhealthy for sensitive people and 34.9% as hazardous).


**Table 5.** Average X-ray fluorescence (XRF) values for trace elements of airborne dust for stations A and B.

## **14. Conclusions**

The present Chapter focused on shedding light on the dust loading, PM concentrations, physical and chemical composition of dust in the Sistan region, southeastern Iran, which constitutes a major dust source region in south west Asia. Sistan region is a closed topographic low basin surrounded by arid and rocky mountains, while its northern part drains the Hilmand river, thus constituting a wetland area known as Hamoun. Hamoun lakes complex have an area about 4500 Km2 with water volumes of 13025 million m3 and play the role of a "water cooler" for the region when they are full of water as the severe winds blow across the lakes.

192 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

characteristics over Sistan and a uniform source of airborne dust.

similar (7.8±0.8 and 8.3±0.9, respectively), due to the presence of silicate and aluminosilicate minerals in most dust samples. The ratios of Mg/Al (0.90±0.16, 0.92±0.12), Ca/Al (3.09±0.19, 3.12±0.19) and Fe/Al (0.51±0.02, 0.49±0.01) at the two stations suggest contributions of clays and Ca-rich (calcite) minerals to the chemical compositions of the airborne dust. In contrast, the Fe/Al ratio is low over Sistan and is nearly half of that found for airborne dust over southwestern Iran and several locations over the globe [72], but is comparable to that found over central Asia [111]. It should be noted that this ratio remains nearly invariant, ranging from 0.47 to 0.54, for all the collected dust samples at both stations and can be a good surrogate for the dust source region, since any variation in Fe/Al mainly corresponds to variations in clay minerals and not to coating during dust transportation [50]. In contrast, the Ca/Al ratio exhibits the highest variations from sample to sample (2.80-3.46), since it is influenced by particle size, with higher values as particle-size increases [72]. Synoptically, all the ratio values and the low standard deviations suggest similarity in geochemical

> Trace Elements Parts per million (ppm) Station A Station B

**Table 5.** Average X-ray fluorescence (XRF) values for trace elements of airborne dust for stations A and B.

The present Chapter focused on shedding light on the dust loading, PM concentrations, physical and chemical composition of dust in the Sistan region, southeastern Iran, which constitutes a major dust source region in south west Asia. Sistan region is a closed topographic low basin surrounded by arid and rocky mountains, while its northern part

**14. Conclusions** 

Severe droughts over the past decades, especially after 1999, have caused desiccation of the Hamoun lakes, leaving a fine layer of sediment that is easily lifted by the wind and therefore making the basin one of the most active sources of dust in south-west Asia [56, 50]. The strong "Levar", especially during the summer season, blows fine sands off the exposed lake bed and deposits this detritus within huge dune bed forms that may cover a hundred or more villages along the former lakeshore. As a consequence, the wildlife around the lake has been negatively impacted and fisheries have been brought to a halt, which also implies an impact on society. The drainage of the Hamoun wetlands, in association with the intense Levar winds in summer, is the main factor responsible for the frequent and massive dust storms over the Sistan region. Analysis of water surface in combination with dust storms showed that the Hamoun dried beds, particularly Hamoun Saberi and Baringak, have a dramatic effect on dust storms as sources of aerosols.

Systematic PM concentrations were measured in Zabol city, affected by the Sistan dust storms, covering the period September 2010 to August 2011. The results show that the PM10 concentrations were considerably higher than the corresponding European Union air quality annual standard. The analysis of the daily PM concentrations showed that the air quality is affected by dust storms from the Sistan desert, which may be very intense during summer. Hamoun, as an intense dust source region, caused a dramatic increase in PM10 concentrations and a deterioration of air quality (65% of the days were considered unhealthy for sensitive people and 34.9% as hazardous).

Dust loading from the Hamoun basin appears to have a significant contributing influence on the development of extreme dust storms, especially during the summer days. This influence firstly seems to depend on the intensity and duration of dust storms, and secondly, on the distance from the source region, the wind speed and altitude. The grain-size distribution of the dust loading was strongly influenced by the distance from the dust source, since grain sizes shifted to larger values towards station B that is closer to the Hamoun basin. Furthermore, the particle size distribution exhibited a shift towards lower values as the altitude increases, with this feature seen to be more obvious amongst larger size particles, while the frequency of particles below 2.5 μm seemed not to be affected by altitude. In general, the regional dust loading and characteristics are subject to significant spatiotemporal variability. This finding necessitates more systematic observations at as many locations as possible around the Hamoun basin in order to improve the understanding of forcing dynamics, transport mechanisms as well as to quantify the dust amounts emitted from the Hamoun basin.

To fully understand mineral dust characteristics and the potential impact on human health, dust mineralogy and geochemical properties were examined in the Sistan region by collecting airborne samples at two stations and soil samples from several locations over

Sistan and the Hamoun basin. The Sistan region is an ideal site to study the nature of dust storms as it receives large amounts of fine alluvial material from the extended Hirmand river system draining much of the Afghanistan highlands, which comprise crystalline basement rocks, Phanerozoic sediments and extensive flood basalts. As a result, large quantities of quartz-rich, feldspar- and mica-bearing silt, as well as mafic material from flood basalt sources and carbonate minerals from dolomites, are transported to the Hamoun wetlands in northern Sistan. Due to droughts at Hamoun and large irrigation projects upstream on the river catchment, extensive desiccation has occurred in the wetlands resulting in large dry lake environments. These have produced large quantities of evaporate minerals to add to the alluvial silts, and the combination of these materials provides the provenance for the airborne dust.

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 195

*Research and Technology Development Centre, Sharda University, Greater Noida, India* 

desert dust sources, Geophysical Research Letters,. 30, NO. 2, 1074

transport. Earth Science Reviews 79, 73-100.

Environ. 113, 1511-1528.

Geophys Res 102:25999–26008

Research doi:10.1016/j.aeolia.2011.12.001

Press, New York, USA.

Environ 60:83–97

Springer, pp: 486

*Department of Geology, Faculty of Natural and Agricultural Sciences, University of Pretoria,* 

[1] Mahowald, N.M., Bryant, R.G., Corral, J., and Steinberger, L. 2003. Ephemeral lakes and

[2] Engelstaedter, S., Tegen, I., Washington, R., 2006. North African dust emissions and

[3] Koren, I., Y. J. Kaufman, R. Washington, M. C. Todd, Y. Rudich, J. V. Martins, and D. Rosenfeld 2006, The Bodele depression: a single spot in the Sahara that provides most of

[5] Orlovsky, L., Orlovsky, N., Durdyev, A. (2005) Dust storms in Turkmenistan. J Arid

[6] Breckle, S.W., Wucherer,W., Liliya A. Dimeyeva, L.A., Nathalia P. Ogar, N.P. 2012. Aralkum - A Man-Made Desert: The Desiccated Floor of the Aral Sea (Central Asia),

[7] Reheis M (1997) Dust deposition of Owens (dry) Lake, 1991–1994: preliminary findings. J

[8] Reheis, M., Budahn, J.R., Lamothe,P.J., and Reynolds, R.L.,, 2009. Compositions of modern dust and surface sediments in the Desert Southwest, United States, Journal Of

[9] Whitney, J. W., 2006. Geology, Water, and Wind in the Lower Helmand Basin, Southern

[10] United Nations Environment Programme (UNEP). 2006. History of Environmental Change in the Sistan Basin Based on Satellite Image Analysis:1976 – 2005. P: 60 [11] Miri A, Moghaddamnia A, Pahlavanravi A, Panjehkeh N (2010) Dust storm frequency

[12] Rashki, A., Kaskaoutis, D.G., Rautenbach, C.J.deW., Eriksson, P.G.,Giang, M, Gupta, P., 2012b. Dust storms and their horizontal dust loading in the Sistan region, Iran. Aeolian

[13] IPCC, (Intergovernmental Panel on Climate Change), 2001. Climate Change 2001: The Scientific Basis. In Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate. J.T. Houghton et al.; Eds, Cambridge Univ.

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after the 1999 drought in the Sistan region, Iran. Clim Res 41:83-90

the mineral dust to the Amazon forest, Environmental Research Letters, 1(1). [4] Baddock, M.C., Bullard, J.E., Bryant, R.G., 2009. Dust source identification using MODIS: A comparison of techniques applied to the Lake Eyre Basin, Australia. Rem. Sens.

Dimitris Kaskaoutis

*Pretoria, South Africa* 

**15. References** 

Patrick Eriksson

Dust aerosol characterization included chemical analysis of major and trace elements by XRF and mineral analysis by XRD. The results showed that quartz, calcite, muscovite, plagioclase and chlorite are the main mineralogical components of the dust, in descending order, over Sistan, and were present in all the selected airborne dust samples. In contrast, significantly lower percentages for enstatite, halite, dolomite, microcline, gypsum, diopside, orthoclase and hornblende were found, since these minerals occurred only in some of the samples at both stations. On the other hand, SiO2, CaO, Al2O3, Na2O, MgO and Fe2O3 were the major elements characterising the dust, while large amounts of F, Cl and S were also found as trace elements. The mineralogy and chemical composition of airborne dust at both stations were nearly the same and quite similar to the soil samples collected at several locations downwind. This suggests that the dust over Sistan is locally emitted, i.e. from the Hamoun basin, and in a few cases can also be long-range transported to distant regions. On the other hand, individual dust storms showed significant differences between either evaporite-dominated aerosols or those characterized by deflation from alluvial silts. These possibly reflect either localized climatic cyclicity or desiccation cycles. However, in some cases the soil samples showed poor comparisons with aerosol compositions, suggesting that dynamic sorting, soil-forming processes and climatic influences, such as rainfall, altered the mineralogy and chemistry in these partially eolian deposits. Sistan is also an ideal site for studying dust storms and enrichment factors relative to crustal norms; the latter factors suggest that the dust is essentially of crustal rather than anthropogenic origin. SEM analyses of the samples indicated that airborne dust has rounded irregular, prismatic and rhombic shapes, with only the finer particles and a few examples of the coarser dust being spherical.

## **Author details**

Alireza Rashki and C.J.deW. Rautenbach *Department of Geography, Geoinformatics and Meteorology, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa Department of Drylands and Desert Management, Faculty of Natural Resources and Environment, Ferdowsi University of Mashhad, Mashhad, Iran* 

Dimitris Kaskaoutis

*Research and Technology Development Centre, Sharda University, Greater Noida, India* 

Patrick Eriksson

194 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

particles and a few examples of the coarser dust being spherical.

*Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria,* 

*Department of Drylands and Desert Management, Faculty of Natural Resources and Environment,* 

*Department of Geography, Geoinformatics and Meteorology,* 

provenance for the airborne dust.

**Author details** 

*South Africa* 

*Iran* 

Alireza Rashki and C.J.deW. Rautenbach

*Ferdowsi University of Mashhad, Mashhad,* 

Sistan and the Hamoun basin. The Sistan region is an ideal site to study the nature of dust storms as it receives large amounts of fine alluvial material from the extended Hirmand river system draining much of the Afghanistan highlands, which comprise crystalline basement rocks, Phanerozoic sediments and extensive flood basalts. As a result, large quantities of quartz-rich, feldspar- and mica-bearing silt, as well as mafic material from flood basalt sources and carbonate minerals from dolomites, are transported to the Hamoun wetlands in northern Sistan. Due to droughts at Hamoun and large irrigation projects upstream on the river catchment, extensive desiccation has occurred in the wetlands resulting in large dry lake environments. These have produced large quantities of evaporate minerals to add to the alluvial silts, and the combination of these materials provides the

Dust aerosol characterization included chemical analysis of major and trace elements by XRF and mineral analysis by XRD. The results showed that quartz, calcite, muscovite, plagioclase and chlorite are the main mineralogical components of the dust, in descending order, over Sistan, and were present in all the selected airborne dust samples. In contrast, significantly lower percentages for enstatite, halite, dolomite, microcline, gypsum, diopside, orthoclase and hornblende were found, since these minerals occurred only in some of the samples at both stations. On the other hand, SiO2, CaO, Al2O3, Na2O, MgO and Fe2O3 were the major elements characterising the dust, while large amounts of F, Cl and S were also found as trace elements. The mineralogy and chemical composition of airborne dust at both stations were nearly the same and quite similar to the soil samples collected at several locations downwind. This suggests that the dust over Sistan is locally emitted, i.e. from the Hamoun basin, and in a few cases can also be long-range transported to distant regions. On the other hand, individual dust storms showed significant differences between either evaporite-dominated aerosols or those characterized by deflation from alluvial silts. These possibly reflect either localized climatic cyclicity or desiccation cycles. However, in some cases the soil samples showed poor comparisons with aerosol compositions, suggesting that dynamic sorting, soil-forming processes and climatic influences, such as rainfall, altered the mineralogy and chemistry in these partially eolian deposits. Sistan is also an ideal site for studying dust storms and enrichment factors relative to crustal norms; the latter factors suggest that the dust is essentially of crustal rather than anthropogenic origin. SEM analyses of the samples indicated that airborne dust has rounded irregular, prismatic and rhombic shapes, with only the finer *Department of Geology, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa* 
