**5. Data set and experimental methods**

In order to address the scientific topics mentioned above multiple ground-based instrumentation and several sets of satellite images (mostly Landsat and MODIS) were used for illustration purposes and for detection of water level in Hamoun and for monitoring of land use – land cover changes, seasonality of dust storms and associated sediments, air quality perspectives, chemical and mineralogical composition of dust over the Sistan region and Hamoun Basin. Within this framework, satellite images from different years were used to identify changes in the lake's surface. Information about dust storm occurrence was obtained from Zabol meteorological station, 5 km from the Hamoun lakes (see Fig. 4). The ground-based measurements were primarily used to compare effects of the Hamoun surface on dust aerosols.

More specifically, the amount of dust loading during dust storms was measured using passive dust traps fixed at two monitoring towers (respectively, at four and eight meters above ground level in altitude), with one meter distance between the adjacent individual traps; the 4 m tower had four traps and the 8 m tower had 8 traps (Fig. 6). The two towers were established in open sites (station A and station B, denoted by red stars in Fig. 2 right panel) close to the dry-bed lake dust source region during the period August 2009 to July 2010. The dust sampler used in the campaign was developed by the Agricultural and Natural Research Center of Sistan (Fig. 6), and is a modified version of the SSDS sampler [66-67]. At the observation sites, the samplers collect airborne dust sediment. The traps were mounted on a stable bracket parallel to the wind direction. The samplers consist of a tube with a diameter of 12 cm. The sediment-laden air passes through a vertical 2.5 cm x 6 cm sampler opening in the middle. Inside the sampler, air speed is reduced and the particles settle in a collection pan at the bottom, while the air discharges through an outlet with a U shape. After each measurement, the samplers were evacuated to make them ready for measuring the following dust events. The collected samples were oven dried at 105 oC for 24 hours, and then, dried samples were weighed using an electronic scale in order to obtain total mass quantities at each sampling height and for each dust storm. The samples were also transported to a laboratory for chemical and mineralogical analysis.

Furthermore, soil samples were collected from topsoil (0–5 cm depth) at several locations in the dry-bed Hamoun lakes and downwind areas. These samples were analyzed to

investigate the chemical and mineralogical characteristics of dust, relevance of inferred sources and contributions to air pollution.

**Figure 6.** Schematic diagram of the dust sampler system.

170 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

coverage than in the mid-1970s [65].

**5. Data set and experimental methods** 

effects of the Hamoun surface on dust aerosols.

to black indicates deeper waters, which, however, do not exceed four meters. (2) By 2001, the Hamoun lakes had vanished since central and southwest Asia were hit by the largest persistent drought anywhere in the world. The only sign of water in this scorched landscape of extensive salt flats (white) is the Chah Nimeh reservoir in the southern part of Sistan (not shown on the satellite image), which is now only used for drinking water. Degraded reed stands in muddy soil are visible as dark green hues at the southern end of Hamoun-i Puzak. In 2003 the Hamoun Basin was covered with water again, but with significantly lower

In order to address the scientific topics mentioned above multiple ground-based instrumentation and several sets of satellite images (mostly Landsat and MODIS) were used for illustration purposes and for detection of water level in Hamoun and for monitoring of land use – land cover changes, seasonality of dust storms and associated sediments, air quality perspectives, chemical and mineralogical composition of dust over the Sistan region and Hamoun Basin. Within this framework, satellite images from different years were used to identify changes in the lake's surface. Information about dust storm occurrence was obtained from Zabol meteorological station, 5 km from the Hamoun lakes (see Fig. 4). The ground-based measurements were primarily used to compare

More specifically, the amount of dust loading during dust storms was measured using passive dust traps fixed at two monitoring towers (respectively, at four and eight meters above ground level in altitude), with one meter distance between the adjacent individual traps; the 4 m tower had four traps and the 8 m tower had 8 traps (Fig. 6). The two towers were established in open sites (station A and station B, denoted by red stars in Fig. 2 right panel) close to the dry-bed lake dust source region during the period August 2009 to July 2010. The dust sampler used in the campaign was developed by the Agricultural and Natural Research Center of Sistan (Fig. 6), and is a modified version of the SSDS sampler [66-67]. At the observation sites, the samplers collect airborne dust sediment. The traps were mounted on a stable bracket parallel to the wind direction. The samplers consist of a tube with a diameter of 12 cm. The sediment-laden air passes through a vertical 2.5 cm x 6 cm sampler opening in the middle. Inside the sampler, air speed is reduced and the particles settle in a collection pan at the bottom, while the air discharges through an outlet with a U shape. After each measurement, the samplers were evacuated to make them ready for measuring the following dust events. The collected samples were oven dried at 105 oC for 24 hours, and then, dried samples were weighed using an electronic scale in order to obtain total mass quantities at each sampling height and for each dust storm. The samples were

also transported to a laboratory for chemical and mineralogical analysis.

Furthermore, soil samples were collected from topsoil (0–5 cm depth) at several locations in the dry-bed Hamoun lakes and downwind areas. These samples were analyzed to These samples were analyzed for major and trace elements and for minerals by applying X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD) techniques, respectively. The samples were prepared for XRD analysis using a back loading preparation method. They were analyzed using a PANalytical X'Pert Pro powder diffractometer with X'Celerator detector and variable divergence and receiving slits with Fe filtered Co-Kα radiation. The phases were identified using X'Pert High score plus software. The relative phase amounts (weights %) were estimated using the Rietveld method (Autoquan Program). Mineral analysis by XRD is the single most important non-destructive technique for the characterization of minerals such as quartz, feldspars, calcite, dolomite, clay, silt and iron oxides in fine dust. Mineral phase analysis by XRD is one of the few techniques that are phase sensitive, rather than chemically sensitive, as is the case with XRF spectrometry. Quantitative mineralogical analyses using the XRD technique have been performed by a number of scientists over the globe [e.g., 68-70, 44, 71-72].

The sample preparation for XRF is made up of two methods, pressed powders and fusions. The former samples were prepared for trace element analyses and the latter for major

element analyses. Each milled sample (<75μm) was combined with a polyvinyl alcohol, transferred into an aluminum cup and manually pressed to ten tons. The pressed powders were dried at 100°C for at least 30 minutes and stored in a desiccator before analyses were conducted. For the fusion method, each milled sample (<75μm) was weighed out in a 1/6 sample to flux (Lithium tetraborate) ratio. These samples were then transferred into mouldable Pt/Au crucibles and fused at 1050°C in a muffle furnace. Aluminum cooling caps were treated with an iodine-ethanol mixture (releasing agent) and placed on top of the crucibles as they cooled. Some samples needed to be treated with an extra 3g of flux if they continued to crack. Finally, all geochemical samples were analyzed using the Thermo Fisher ARL 9400 XP+ Sequential XRF. The Quantas software package was used for the major element analyses and the WinXRF software package was used for the trace element analyses. The concentrations of the major elements are reported as oxides in weight percentages, while the trace element concentrations are reported as elements in parts per million (ppm).

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 173

winter (9 to 12 oC) and high (~35 oC) in summer, following the common pattern found in the northern Mid-latitudes. During the summer period the maximum T often goes up to 46 or 48 oC causing an extremely large diurnal variation, which is a characteristic of many arid environments. RH illustrates an inverse annual variation with larger values in winter (50 to 57%) and very low values in summer (~25%), which are about 10 to 15% during daytime. During the period October to April P values are generally high (1020 to 1024 hPa in winter), which is above the standard mean sea level value of 1013.25 hPa. P values decrease during summer (~ 996 hPa in July) as a result of the Indian thermal low that develops over the entire south Asia during summer monsoon months. This has a direct impact on the intensity of the winds over the region, which has a monthly mean of as high as 12 m.s-1 during June and July with frequent gusts of above 20 to 25 m.s-1. In contrast, during late autumn and

**Figure 7.** Monthly mean variation of air Temperature, Relative Humidity and atmospheric pressure in

The dust storms over a region cause several climatic implications, environmental and human concerns [16, 75,18, 76, 36] and can be examined via multiple instrumentation and techniques. Among others, the analysis of the visibility records can constitute a powerful tool for monitoring of the seasonal and inter-annual variation of the dust storms, since the main result of such phenomena is the limitation of visibility and deterioration of air quality. The annual variation of visibility (as the main indicator for the dust storms) over Sistan follows a clear annual pattern, with large values in winter, usually above 10 km, and very low in summer (< 4 km on average) as analyzed from meteorological observations taken at Zabol (Fig. 8). A power-decreasing curve relation associated with 93% of the variance was observed between wind speed and visibility [12]. This inverse relation indicates that the wind speed does not act

**7. Temporal changes of Hamoun dry lake beds and dust storms** 

winter months the wind speed is confined to ~3 to 4 m.s-1 [12].

Zabol during the period 1963 –2010.

Furthermore, in order to provide analysis of the air quality, PM10 concentration measurements were obtained by using an automatic Met One BAM 1020 beta gauge monitor (Met One, Inc.,) over Zabol. The instrument measures PM10 concentrations (in μg.m-3) with a temporal resolution of one hour. The measurements were carried out at the Environmental Institute of Sistan located at the outskirts of Zabol during the period September 2010 to September 2011 (total of 373 days). The recording station is close to the Hamoun basin and is placed in the main pathway of the dust storms of the Sistan region. The hourly measured PM10 data were daily-averaged, from which the monthly values and seasonal variations were obtained. For further assessing the air quality over Zabol, the PM10 concentrations were used to calculate an Air Quality Index (AQI) [52].

## **6. Meteorology and climatology over Sistan**

The climate over Sistan is arid, with low annual average precipitation of ~55 mm occurring mainly in the winter (December to February) and evaporation exceeding ~4000 mmyear-1 [58]. During summer, the area is under the influence of a low pressure system attributed to the Indian thermal low that extends further to the west as a consequence of the south Asian monsoon system. These low pressure conditions are the trigger for the development of the Levar northerly wind, commonly known as the "120-day wind" [73], causing frequent dust and sand storms, especially during summer (June to August) [74, 56] and contributing to the deterioration of air quality [52]. Therefore, one of the main factors affecting the weather conditions over the region is the strong winds rendering Sistan as one of the windiest deserts in the world. These winds blow continuously in spring and summer (from May to September), and on some days during winter, and have significant impacts on the landscape and the lives of the local inhabitants.

The annual variation of mean Temperature (T), Relative Humidity (RH) and atmospheric Pressure (P) over Zabol (a large city in the Sistan region) during the period 1963 to 2010 is shown in Fig 7. The monthly mean T exhibits a clear annual pattern with low values in the winter (9 to 12 oC) and high (~35 oC) in summer, following the common pattern found in the northern Mid-latitudes. During the summer period the maximum T often goes up to 46 or 48 oC causing an extremely large diurnal variation, which is a characteristic of many arid environments. RH illustrates an inverse annual variation with larger values in winter (50 to 57%) and very low values in summer (~25%), which are about 10 to 15% during daytime. During the period October to April P values are generally high (1020 to 1024 hPa in winter), which is above the standard mean sea level value of 1013.25 hPa. P values decrease during summer (~ 996 hPa in July) as a result of the Indian thermal low that develops over the entire south Asia during summer monsoon months. This has a direct impact on the intensity of the winds over the region, which has a monthly mean of as high as 12 m.s-1 during June and July with frequent gusts of above 20 to 25 m.s-1. In contrast, during late autumn and winter months the wind speed is confined to ~3 to 4 m.s-1 [12].

172 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

were used to calculate an Air Quality Index (AQI) [52].

**6. Meteorology and climatology over Sistan** 

and the lives of the local inhabitants.

million (ppm).

element analyses. Each milled sample (<75μm) was combined with a polyvinyl alcohol, transferred into an aluminum cup and manually pressed to ten tons. The pressed powders were dried at 100°C for at least 30 minutes and stored in a desiccator before analyses were conducted. For the fusion method, each milled sample (<75μm) was weighed out in a 1/6 sample to flux (Lithium tetraborate) ratio. These samples were then transferred into mouldable Pt/Au crucibles and fused at 1050°C in a muffle furnace. Aluminum cooling caps were treated with an iodine-ethanol mixture (releasing agent) and placed on top of the crucibles as they cooled. Some samples needed to be treated with an extra 3g of flux if they continued to crack. Finally, all geochemical samples were analyzed using the Thermo Fisher ARL 9400 XP+ Sequential XRF. The Quantas software package was used for the major element analyses and the WinXRF software package was used for the trace element analyses. The concentrations of the major elements are reported as oxides in weight percentages, while the trace element concentrations are reported as elements in parts per

Furthermore, in order to provide analysis of the air quality, PM10 concentration measurements were obtained by using an automatic Met One BAM 1020 beta gauge monitor (Met One, Inc.,) over Zabol. The instrument measures PM10 concentrations (in μg.m-3) with a temporal resolution of one hour. The measurements were carried out at the Environmental Institute of Sistan located at the outskirts of Zabol during the period September 2010 to September 2011 (total of 373 days). The recording station is close to the Hamoun basin and is placed in the main pathway of the dust storms of the Sistan region. The hourly measured PM10 data were daily-averaged, from which the monthly values and seasonal variations were obtained. For further assessing the air quality over Zabol, the PM10 concentrations

The climate over Sistan is arid, with low annual average precipitation of ~55 mm occurring mainly in the winter (December to February) and evaporation exceeding ~4000 mmyear-1 [58]. During summer, the area is under the influence of a low pressure system attributed to the Indian thermal low that extends further to the west as a consequence of the south Asian monsoon system. These low pressure conditions are the trigger for the development of the Levar northerly wind, commonly known as the "120-day wind" [73], causing frequent dust and sand storms, especially during summer (June to August) [74, 56] and contributing to the deterioration of air quality [52]. Therefore, one of the main factors affecting the weather conditions over the region is the strong winds rendering Sistan as one of the windiest deserts in the world. These winds blow continuously in spring and summer (from May to September), and on some days during winter, and have significant impacts on the landscape

The annual variation of mean Temperature (T), Relative Humidity (RH) and atmospheric Pressure (P) over Zabol (a large city in the Sistan region) during the period 1963 to 2010 is shown in Fig 7. The monthly mean T exhibits a clear annual pattern with low values in the

**Figure 7.** Monthly mean variation of air Temperature, Relative Humidity and atmospheric pressure in Zabol during the period 1963 –2010.

## **7. Temporal changes of Hamoun dry lake beds and dust storms**

The dust storms over a region cause several climatic implications, environmental and human concerns [16, 75,18, 76, 36] and can be examined via multiple instrumentation and techniques. Among others, the analysis of the visibility records can constitute a powerful tool for monitoring of the seasonal and inter-annual variation of the dust storms, since the main result of such phenomena is the limitation of visibility and deterioration of air quality. The annual variation of visibility (as the main indicator for the dust storms) over Sistan follows a clear annual pattern, with large values in winter, usually above 10 km, and very low in summer (< 4 km on average) as analyzed from meteorological observations taken at Zabol (Fig. 8). A power-decreasing curve relation associated with 93% of the variance was observed between wind speed and visibility [12]. This inverse relation indicates that the wind speed does not act

as a ventilation phenomenon over Zabol, as usually occurs in coastal urban environments with local sea-breeze cells [77], but rather as a factor responsible for the deterioration of visibility, since the intense Levar winds are the cause of the dust outbreaks over Sistan. Therefore, the major dust storms over the region are associated with intense winds of northwesterly direction that are responsible for the deterioration of visibility to lower than 100 m in many cases.

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 175

noted that Zabol is located at the downwind direction of dust storms that normally originate

**Figure 9.** Flow chart of the seasonal wind speed and direction in Zabol during the period 1963-2010. The percentage of calm periods is shown at the bottom of each wind rose. The thickest bar represents wind speeds in excess of 12 m/s); (b) year-to-year variation of the visibility recordings at Zabol

The water levels in the Hamoun lakes change considerably from year to year as has been discussed above. Table 1 summarizes the percentage of water surface in July in the Hamoun lakes, as well as the annual precipitation and number of dusty days during the period 1985-2005. Yearly variations of Hamoun lakes water surface identified four periods from 1985 to 2005: [10]: 1. A low-water period from 1985-1988: the Hamoun dried out or shrunk to a very small

2. A high-water period from 1989-1993: there was considerable inflow for five years, during which time the Hamoun only shrunk below the previous period's maximum

3. A medium-water period from 1994-1999: a dynamic balance of inflow and outflow

4. A dry period from 2000-present: the inflow ceased and a catastrophic drought ensued

On the other hand, Table 2 summarizes the correlation coefficients between the percentage of dried beds in July, precipitation and number of dusty days, i.e. the parameters that are included in Table 1. The analysis shows that precipitation has a direct effect on water levels (r=0.63 for Hamoun Saberi). On the other hand, in years with high precipitation the lakes had high water surface. Hamoun Saberi is also affected by the Farah river that has a closer watershed, but this correlation is low for both Hamoun Hirmand and Hamoun Puzak (r= 0.35 and r=0.54 respectively). The correlation between dusty days and percentage of dried Hamoun beds (100-percent of water surface) shows high correlation coefficient values regarding Hamoun Saberi and Baringak (r=0.88 and r=0.82 respectively) and lower correlation for Hamoun Hirmand (r= 0.63). The high correlation for the Hamoun Saberi and Baringak indicates that Sistan dust storms are directly affected by the north and

size almost every year, but there was some inflow every year.

maintained a reasonably high minimum water volume every year.

except for a flood in 2005 that immediately dried up before 2006.

from Hamoun (Fig. 2).

meteoroological station.

levels for a very short time.

**Figure 8.** Monthly mean variation of the visibility (km) and wind speed (ms-1) in Zabol during the period 1963–2009.

Although the visibility exhibits a clear annual pattern (Fig. 8) suggesting that the summer season is the favourable period for the occurrence of frequent and intense dust storms, longterm data series over Zabol (1963-2009) show that it contains considerable year-to-year variations (Fig. 9b). Focusing on recent years, the days with visibility <= 2 km have been dramatically increased from about 20 during 1995 to 1999 to >100 during 2000 to 2001. This is attributed to a severe drought period that dried the largest part of the Hamoun wetlands (see Fig. 5) and favored the alluvial uplift, as well as the frequency and mass intensity of dust storms that affected the visibility over Sistan (Fig. 9b). However, in the 2000s the days with very low visibility seem to have a decreasing trend, but remaining above the standards of the climatological mean. It is, therefore, concluded that the regional and synoptic meteorology (mainly precipitation) is strongly linked to land use – land cover changes over Hamoun and then, to dust outbreaks over Sistan region.

In contrast, the annual variation of the wind speed (Fig. 9a) exhibits an opposite pattern with higher intensities during summer (June and July) and lower in winter. As far as the wind direction is concerned, it is found from the Zabol data series that the northwestern direction clearly dominates, being more apparent in summer, while high percentages for intense winds are also associated with a northwesterly flow (Fig. 9a). The probability for intense winds to blow from other directions is low; summer winds are much more intense with ~27% of wind speeds above 11 ms-1, while calm conditions are limited to 3% against 19% and 20% for autumn and winter, respectively. The higher frequency and intensity of northwestern winds is the reason for the frequent dust storms that affect Zabol. It is to be noted that Zabol is located at the downwind direction of dust storms that normally originate from Hamoun (Fig. 2).

174 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

**Vis=26.67xW D -0.81, R <sup>2</sup>**

Hamoun and then, to dust outbreaks over Sistan region.

period 1963–2009.

**Visibility (km)**

as a ventilation phenomenon over Zabol, as usually occurs in coastal urban environments with local sea-breeze cells [77], but rather as a factor responsible for the deterioration of visibility, since the intense Levar winds are the cause of the dust outbreaks over Sistan. Therefore, the major dust storms over the region are associated with intense winds of northwesterly direction that are responsible for the deterioration of visibility to lower than 100 m in many cases.

**=0.93**

 visibility wind speed

**Figure 8.** Monthly mean variation of the visibility (km) and wind speed (ms-1) in Zabol during the

Although the visibility exhibits a clear annual pattern (Fig. 8) suggesting that the summer season is the favourable period for the occurrence of frequent and intense dust storms, longterm data series over Zabol (1963-2009) show that it contains considerable year-to-year variations (Fig. 9b). Focusing on recent years, the days with visibility <= 2 km have been dramatically increased from about 20 during 1995 to 1999 to >100 during 2000 to 2001. This is attributed to a severe drought period that dried the largest part of the Hamoun wetlands (see Fig. 5) and favored the alluvial uplift, as well as the frequency and mass intensity of dust storms that affected the visibility over Sistan (Fig. 9b). However, in the 2000s the days with very low visibility seem to have a decreasing trend, but remaining above the standards of the climatological mean. It is, therefore, concluded that the regional and synoptic meteorology (mainly precipitation) is strongly linked to land use – land cover changes over

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

**Wind speed (ms-1**

**)**

**M onth**

In contrast, the annual variation of the wind speed (Fig. 9a) exhibits an opposite pattern with higher intensities during summer (June and July) and lower in winter. As far as the wind direction is concerned, it is found from the Zabol data series that the northwestern direction clearly dominates, being more apparent in summer, while high percentages for intense winds are also associated with a northwesterly flow (Fig. 9a). The probability for intense winds to blow from other directions is low; summer winds are much more intense with ~27% of wind speeds above 11 ms-1, while calm conditions are limited to 3% against 19% and 20% for autumn and winter, respectively. The higher frequency and intensity of northwestern winds is the reason for the frequent dust storms that affect Zabol. It is to be

**Figure 9.** Flow chart of the seasonal wind speed and direction in Zabol during the period 1963-2010. The percentage of calm periods is shown at the bottom of each wind rose. The thickest bar represents wind speeds in excess of 12 m/s); (b) year-to-year variation of the visibility recordings at Zabol meteoroological station.

The water levels in the Hamoun lakes change considerably from year to year as has been discussed above. Table 1 summarizes the percentage of water surface in July in the Hamoun lakes, as well as the annual precipitation and number of dusty days during the period 1985-2005. Yearly variations of Hamoun lakes water surface identified four periods from 1985 to 2005: [10]:


On the other hand, Table 2 summarizes the correlation coefficients between the percentage of dried beds in July, precipitation and number of dusty days, i.e. the parameters that are included in Table 1. The analysis shows that precipitation has a direct effect on water levels (r=0.63 for Hamoun Saberi). On the other hand, in years with high precipitation the lakes had high water surface. Hamoun Saberi is also affected by the Farah river that has a closer watershed, but this correlation is low for both Hamoun Hirmand and Hamoun Puzak (r= 0.35 and r=0.54 respectively). The correlation between dusty days and percentage of dried Hamoun beds (100-percent of water surface) shows high correlation coefficient values regarding Hamoun Saberi and Baringak (r=0.88 and r=0.82 respectively) and lower correlation for Hamoun Hirmand (r= 0.63). The high correlation for the Hamoun Saberi and Baringak indicates that Sistan dust storms are directly affected by the north and

northwestern winds flowing through the Saberi. The year-to-year variation of the dusty days and the percentage (%) of dried bed lakes in Baringak and Hamoun Saberi (Fig. 10) indicates a co-variation of the examined parameters, thus suggesting that the land use – land cover changes play a major role in the occurrence of dust storms over Sistan region.

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 177

0

20

40

60

**Dried bed (%)**

80

100

**1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006**

Year

**Figure 10.** Yearly variability of the dusty days (visibility <= 2km) over Sistan region with association to percentage of Hamoun dried beds (1985-2005). The lower coverage of the Hamoun Basin by water (high

Dust activity is a function of several parameters, such as topography, rainfall, soil moisture, surface winds, regional meteorology, boundary layer height and convective activity [78-79.

Data on dust loading are available at only a few places around the world [e.g.80-84] and those presented here are the first for the Sistan region. Hence, obtaining measurements of horizontal dust flux will significantly increase our understanding of wind erosion and dust influences. Apart from the natural emissions of dust, [85] identified two ways in which human activities can influence dust emissions: (a) by changes in land use, which alter the potential for dust emission, and (b) by perturbing local climate that, in turn, alter dust emissions. As has been discussed above, both ways are considerably active over the Sistan

The dust loading measured at the two stations close to the Hamoun basin for several dust events during the period August 2009 to July 2010 is plotted in Fig. 11. In the same graph, meteorological data from the Zabol station that give information about the duration of dust events (for the examined days as well as on the preceding or succeeding days, i.e. about 2-3 days before the peak-day of the dust storm) and daily mean and maximum wind speeds, are also plotted. The results of the average dust loading measured at eight heights at station B and at four heights at station A reveal considerable variation, ranging from ~0.10 to ~2.5 kgm-2. In general, the highest dust loading is observed for dust events occurring in summer, but intense dust storms can also take place in winter, since the Hamoun basin is an active dust source region throughout the year. The dust loading is highly correlated with the duration of the dust storms, as shown from their correlation, with the linear regressions being statistically significant at the 0.99% confidence level (Fig. 12). Apart from the strong linkage to the duration of dust storms, the dust loading at both stations also seems to have a dependence on the daily mean and maximum wind speeds (not presented). However, this

percentage of dried beds) corresponds to higher number of dusty days over Sistan region.

 Du sty d ays B arin ga k Hamoun S aberi

**20**

**8. Dust loading measurements** 

region and Hamoun Basin.

**40**

**60**

**Dusty days**

**80**

**100**

**120**


**Table 1.** Yearly variability of percentage of water surface in Hamoun lakes in July, annual precipitation and the dusty days (visibility <= 2km) over Sistan region


\*\* Correlation is significant at the 0.01 level

**Table 2.** Correlations between percent of Hamoun dried beds in July and dusty days (1985-2005).

**Figure 10.** Yearly variability of the dusty days (visibility <= 2km) over Sistan region with association to percentage of Hamoun dried beds (1985-2005). The lower coverage of the Hamoun Basin by water (high percentage of dried beds) corresponds to higher number of dusty days over Sistan region.

## **8. Dust loading measurements**

176 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

and the dusty days (visibility <= 2km) over Sistan region

Hamoun Hirmand 0.84\*\* 0.80\*\* 1

Hamoun Puzak 0.80\*\* 0.89\*\* 0.74\*\* 1

Saberi

Precipitation -0.59\*\* -0.63\*\* -0.35 -0.54 1

Dusty days 0.82\*\* 0.88\*\* 0.60\*\* 0.81\*\* -0.730\*\* 1

**Table 2.** Correlations between percent of Hamoun dried beds in July and dusty days (1985-2005).

Hamoun Hirmand Hamoun

Puzak Precipitation Dusty

days

Baringak Hamoun

Hamoun Saberi 0.96\*\* 1

\*\* Correlation is significant at the 0.01 level

Baringak 1

northwestern winds flowing through the Saberi. The year-to-year variation of the dusty days and the percentage (%) of dried bed lakes in Baringak and Hamoun Saberi (Fig. 10) indicates a co-variation of the examined parameters, thus suggesting that the land use – land

**Year Baringak Saberi Hirmand Puzak precipitation Dusty days**  1985 0 30 7 35 25.6 88 1986 35 65 12 53 72.8 30 1987 25 40 2 53 8.7 91 1988 15 50 6 50 69.5 62 1989 90 92 60 54 26.1 38 1990 90 98 70 72 96.1 37 1991 80 95 90 80 85.8 41 1992 80 98 80 93 80.9 33 1993 75 95 70 60 52.4 46 1994 43 60 20 60 116.6 39 1995 48 66 7 62 76.2 21 1996 62 90 47 70 84.3 18 1997 60 85 25 60 76.4 23 1998 80 100 73 60 61.4 22 1999 72 90 25 60 87.7 28 2000 0 12 0 0 26.8 116 2001 0 0 0 0 7.2 110 2002 0 5 0 0 37.5 88 2003 0 0 0 0 32.3 92 2004 0 0 0 0 51.1 80 2005 80 90 18 32 129.5 41 **Table 1.** Yearly variability of percentage of water surface in Hamoun lakes in July, annual precipitation

cover changes play a major role in the occurrence of dust storms over Sistan region.

Dust activity is a function of several parameters, such as topography, rainfall, soil moisture, surface winds, regional meteorology, boundary layer height and convective activity [78-79.

Data on dust loading are available at only a few places around the world [e.g.80-84] and those presented here are the first for the Sistan region. Hence, obtaining measurements of horizontal dust flux will significantly increase our understanding of wind erosion and dust influences. Apart from the natural emissions of dust, [85] identified two ways in which human activities can influence dust emissions: (a) by changes in land use, which alter the potential for dust emission, and (b) by perturbing local climate that, in turn, alter dust emissions. As has been discussed above, both ways are considerably active over the Sistan region and Hamoun Basin.

The dust loading measured at the two stations close to the Hamoun basin for several dust events during the period August 2009 to July 2010 is plotted in Fig. 11. In the same graph, meteorological data from the Zabol station that give information about the duration of dust events (for the examined days as well as on the preceding or succeeding days, i.e. about 2-3 days before the peak-day of the dust storm) and daily mean and maximum wind speeds, are also plotted. The results of the average dust loading measured at eight heights at station B and at four heights at station A reveal considerable variation, ranging from ~0.10 to ~2.5 kgm-2. In general, the highest dust loading is observed for dust events occurring in summer, but intense dust storms can also take place in winter, since the Hamoun basin is an active dust source region throughout the year. The dust loading is highly correlated with the duration of the dust storms, as shown from their correlation, with the linear regressions being statistically significant at the 0.99% confidence level (Fig. 12). Apart from the strong linkage to the duration of dust storms, the dust loading at both stations also seems to have a dependence on the daily mean and maximum wind speeds (not presented). However, this

dependence was found to be more intense and statistically significant (at the 95% confidence level) at station B, which is located closer to the dust source, whereas for station A the correlation was not found to be statistically significant. This finding emphasizes the strong effect of the wind speed on dust erosion and transportation, as well as on dust loading, at least for areas close to dust sources. However, the results show that the main factor that controls the dust loading at both stations is the duration of the dust storms, and secondly the wind speed. The role of the wind might have been found to be more critical if measurements were taken at the sampler stations instead of using the meteorological data from Zabol. The analysis showed that the total dust loading for the 19 events of measurements at station A is 16.9 kg m-2 corresponding to 0.88 kg m-2 per event, whereas at station B the measurements yielded 15.8 kg m-2 (17 events), corresponding to 0.93 kg m-2 per event. The larger dust loading at station B is attributed to the smaller distance from the source region.

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 179

> Station A Station B

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

**Sediment loading (kgm-2)**

**(b) Station B**

region, meaning that uplift and newly transported dust concentration is higher near the surface. On the other hand, at station A that is located about 20 km away, the dust loading presents larger values up to 3 m since the near-ground dust particles have already been deposited near the source, and as the distance increases so does the dust-plume height. The diurnal variability of the dust loading at the two stations (not presented) showed increased mass concentrations during daytime that can be explained by enhanced convection and turbulent mixing in a deepened boundary layer. Furthermore, the local winds are stronger

**Figure 12.** Correlation between dust loading measurements and duration of dust storm events for 19

Y=29.55(4.92) + 6.75(5.98) r=0.84, P<0.0001 [Station B]

Y=33.81(5.04) + 4.06(5.64) r=0.85, P<0.0001 [Station A]

0.0 0.5 1.0 1.5 2.0 2.5 3.0

**Sediment loading (Kgm-2)**

 **Figure 13.** Height variation of the dust loading at stations A (a) and at station B (b) for several dust storm days. Green colors are loadings for winter, yellow for spring, red for summer and blue for autumn.

**Height (m)**

during daytime due to thermal convections.

days at station A and 17 days at station B.

4.0 **(a) Station A**

1.0

1.5

2.0

2.5

**Height (m)**

3.0

3.5

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

**Sediment loading (kgm-2)**

0

20

40

60

**Dust duration (hour)**

80

100

120

**Figure 11.** Average dust loading (kgm-2) during various dust events in the Sistan region as measured at the 4m (station A) and 8m (station B) monitoring towers. The duration of dust events (hours), as well as the mean and maximum wind speeds on the dusty days were obtained from the Zabol meteorological station.

Figure 13 illustrates the height variation in dust loading during the dust storms measured at station A (19 days, up to 4m in height) and station B (17 days, up to 8m in height). Contrasting height variations measured during intense dust storms occurred between the two stations, while similar variations correspond to moderate and low dust storm events. More specifically, the dust loading shows an increase (decrease) with height in station A (station B), revealing a difference in the dust transport mechanisms. This finding can be explained by considering the fact that station B is located closer to the Hamoun dust source region, meaning that uplift and newly transported dust concentration is higher near the surface. On the other hand, at station A that is located about 20 km away, the dust loading presents larger values up to 3 m since the near-ground dust particles have already been deposited near the source, and as the distance increases so does the dust-plume height. The diurnal variability of the dust loading at the two stations (not presented) showed increased mass concentrations during daytime that can be explained by enhanced convection and turbulent mixing in a deepened boundary layer. Furthermore, the local winds are stronger during daytime due to thermal convections.

178 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

source region.

dependence was found to be more intense and statistically significant (at the 95% confidence level) at station B, which is located closer to the dust source, whereas for station A the correlation was not found to be statistically significant. This finding emphasizes the strong effect of the wind speed on dust erosion and transportation, as well as on dust loading, at least for areas close to dust sources. However, the results show that the main factor that controls the dust loading at both stations is the duration of the dust storms, and secondly the wind speed. The role of the wind might have been found to be more critical if measurements were taken at the sampler stations instead of using the meteorological data from Zabol. The analysis showed that the total dust loading for the 19 events of measurements at station A is 16.9 kg m-2 corresponding to 0.88 kg m-2 per event, whereas at station B the measurements yielded 15.8 kg m-2 (17 events), corresponding to 0.93 kg m-2 per event. The larger dust loading at station B is attributed to the smaller distance from the

**Figure 11.** Average dust loading (kgm-2) during various dust events in the Sistan region as measured at the 4m (station A) and 8m (station B) monitoring towers. The duration of dust events (hours), as well as the mean and maximum wind speeds on the dusty days were obtained from the Zabol meteorological station.

Figure 13 illustrates the height variation in dust loading during the dust storms measured at station A (19 days, up to 4m in height) and station B (17 days, up to 8m in height). Contrasting height variations measured during intense dust storms occurred between the two stations, while similar variations correspond to moderate and low dust storm events. More specifically, the dust loading shows an increase (decrease) with height in station A (station B), revealing a difference in the dust transport mechanisms. This finding can be explained by considering the fact that station B is located closer to the Hamoun dust source

**Figure 12.** Correlation between dust loading measurements and duration of dust storm events for 19 days at station A and 17 days at station B.

**Figure 13.** Height variation of the dust loading at stations A (a) and at station B (b) for several dust storm days. Green colors are loadings for winter, yellow for spring, red for summer and blue for autumn.

## **9. PM10 measurements**

In order to provide a first ever in-situ analysis of the air quality over Sistan, PM10 concentration measurements were obtained by using an automatic Met One BAM 1020 beta gauge monitor (Met One, Inc.,) at Zabol [12]. The instrument measures PM10 concentrations (in μg.m-3) with a temporal resolution of one hour. The measurements were carried out at the Environmental Institute in Sistan located at the outskirts of Zabol during the period September 2010 to August 2011. The recording station is close to the Hamoun basin and is placed in the main pathway of the dust storms in the Sistan region. The hourly measured PM10 data were daily-averaged, from which the monthly values and seasonal variations were obtained (Table 3). For further assessing the air quality over Zabol, the PM10 concentrations were used to calculate the Air Quality Index (AQI).

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 181

**Figure 14.** Daily PM10 concentrations at Zabol during the period 28/8/2010 to 10/9/2011.

**2011/01/01**

**Figure 15.** Frequency (%) distribution of the daily PM10 values for each season in Zabol.

**PM10 Concentration (g/m)<sup>3</sup>**

0-54 55-154 155-254 255-354 355-424 >425

**Summer**

Levar winds in September favouring the dust storms over Sistan.

**2010/08/01**

**PM10 Concentration g m-3)**

**Frequency of Occurrence (%)**

**2010/09/01** **2010/10/01** **2010/11/01** **2010/12/01**

The frequency of occurrence of PM10 concentrations for each season over Zabol is depicted in Fig. 15. In summer ~60% of the PM10 values were higher than 425 μg.m-3, while the lower PM10 values occur in winter and spring with larger frequency in the 55-154 μg.m-3 interval. A very significant finding is the very low frequency for PM10 concentrations below ~400 μg.m-3 in summer, suggesting an extremely turbid atmosphere with frequent dust storms and near absence of clear or relatively clear conditions over Sistan during summer. Autumn also presents high frequency in the >425 μg.m-3 interval that might be due to continuation of the

**2011/02/01** **2011/03/01**

Date

**Winter Spring**

**2011/04/01** **2011/05/01** **2011/06/01**

0-54 55-154 155-254 255-354 355-424 >425

**Autumn**

**2011/07/01** **2011/08/01**

**2011/09/01**


**Table 3.** Monthly mean, daily maximum and daily minimum PM10 concentrations in Zabol during the period September 2010 to August 2011.

The results show extremely large PM10 concentrations at Zabol (see Fig. 14). Even the mean values are much higher than the most risky and dangerous maximum levels provided by the U.S. Environmental Protection Agency (397 g.m-3). Throughout the year, and especially during the period June to October, the area suffers from severe pollution since even the lower PM10 values are above 100 μg.m-3, while the maximum ones are usually above 1000 μg.m-3. On the other hand, extreme PM10 measurements associated with severe dust events may also occur in other months, for example like December. Daily PM10 concentrations during major dust storms are about 10 to 20 times above the standard levels. Regarding the monthly mean PM10 concentrations, the results show extremely large values (>500 μg.m-3) during the period June to October, reaching up to 847 μg.m-3 in July.

**Figure 14.** Daily PM10 concentrations at Zabol during the period 28/8/2010 to 10/9/2011.

were used to calculate the Air Quality Index (AQI).

period September 2010 to August 2011.

In order to provide a first ever in-situ analysis of the air quality over Sistan, PM10 concentration measurements were obtained by using an automatic Met One BAM 1020 beta gauge monitor (Met One, Inc.,) at Zabol [12]. The instrument measures PM10 concentrations (in μg.m-3) with a temporal resolution of one hour. The measurements were carried out at the Environmental Institute in Sistan located at the outskirts of Zabol during the period September 2010 to August 2011. The recording station is close to the Hamoun basin and is placed in the main pathway of the dust storms in the Sistan region. The hourly measured PM10 data were daily-averaged, from which the monthly values and seasonal variations were obtained (Table 3). For further assessing the air quality over Zabol, the PM10 concentrations

January 196 29 597 February 147 13 787 March 262 21 2698 April 224 97 515 May 322 71 1276 June 627 100 1875 July 847 110 2007 August 807 155 2448 September 564 88 1046 October 531 100 2339 November 200 66 737 December 476 84 3094 Winter 273 13 3094 Spring 270 21 2698 Summer 716 100 2448 Autumn 484 66 2339 **Table 3.** Monthly mean, daily maximum and daily minimum PM10 concentrations in Zabol during the

The results show extremely large PM10 concentrations at Zabol (see Fig. 14). Even the mean values are much higher than the most risky and dangerous maximum levels provided by the U.S. Environmental Protection Agency (397 g.m-3). Throughout the year, and especially during the period June to October, the area suffers from severe pollution since even the lower PM10 values are above 100 μg.m-3, while the maximum ones are usually above 1000 μg.m-3. On the other hand, extreme PM10 measurements associated with severe dust events may also occur in other months, for example like December. Daily PM10 concentrations during major dust storms are about 10 to 20 times above the standard levels. Regarding the monthly mean PM10 concentrations, the results show extremely large values (>500 μg.m-3)

during the period June to October, reaching up to 847 μg.m-3 in July.

Monthly Mean Daily minimum Daily maximum PM10 (g.m-3) PM10 (g.m-3) PM10 (g.m-3)

**9. PM10 measurements** 

The frequency of occurrence of PM10 concentrations for each season over Zabol is depicted in Fig. 15. In summer ~60% of the PM10 values were higher than 425 μg.m-3, while the lower PM10 values occur in winter and spring with larger frequency in the 55-154 μg.m-3 interval. A very significant finding is the very low frequency for PM10 concentrations below ~400 μg.m-3 in summer, suggesting an extremely turbid atmosphere with frequent dust storms and near absence of clear or relatively clear conditions over Sistan during summer. Autumn also presents high frequency in the >425 μg.m-3 interval that might be due to continuation of the Levar winds in September favouring the dust storms over Sistan.

**Figure 15.** Frequency (%) distribution of the daily PM10 values for each season in Zabol.
