**1. Introduction**

162 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

atmosphere. Journal Geophysical Research 2007;112, D16109.

[103] McCormack JP, Siskind DE, Hood LL. Solar–QBO interaction and its impact on stratospheric ozone in a zonally averaged photochemical transport model of the middle

> Changes in the frequency and extent of natural inundation occurring on large permanent and ephemeral lake systems may lead to significant fluctuations in regional dust loading on both a seasonal and an inter-annual basis [1]. As surface water diversion increases, arid-land surfaces that were previously wet or stabilized by vegetation are increasingly susceptible to deflation by wind, resulting in desertification and increase in dust outbreaks [2-4]. Desiccation of lake beds, whether due to drought or to water diversion schemes, as in the Aral Sea in Turkmenistan [5,6], Owens lake in California [7,8], lake Eyre in Australia, Hamoun lakes in Iran [9-12], can lead to increased dust storm activity. Thus, some dust may be derived from dried lake beds and can be highly saline, while the finest aerosols can be injurious to health. Anthropogenic sources were previously considered as important dust contributors [13], but more recent estimates of only 5-7% of total mineral dust from such sources gives major importance to natural sources [14]. Each year, several billion tons of soil-dust are entrained into the atmosphere playing a vital role in solar irradiance attenuation, and affects marine environments, atmospheric dynamics and weather [15-20].

> Atmospheric aerosols affect the global climatic system in many ways, i.e. by attenuating the solar radiation reaching the ground, modifying the solar spectrum, re-distributing the earthatmosphere energy budget and influencing cloud microphysics and the hydrological cycle. Mineral dust plays an important role in the optical, physical and chemical processes in the atmosphere, while dust deposition adds exogenous mineral and organic material to terrestrial surfaces, having a significant impact on the Earth's ecosystems and biogeochemical cycles. The impact of dust aerosols in the Earth's system depends mainly on particle characteristics such as size, shape and mineralogy [21], which are initially determined by the terrestrial sources from which the soil sediments are entrained and from

© 2012 Rashki et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Rashki et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

their chemical composition [22]. Size distribution is a key parameter to characterize the aerosol chemical, physical, optical properties and their effects on health. The lower and upper size limits of dust aerosols are from a few nanometers to ~100μm and aerosol properties change substantially over this size range. Several studies demonstrated that airborne Particulate Matter (PM) has an impact on climate [23], biogeochemical cycling in ecosystems [24], visibility [25] and human health [26-28]. Over recent years in the public health domain the PM concentration has become a topic of considerable importance, since epidemiological studies have shown that exposure to particulates with aerodynamic diameters of < 10 μm (PM10) and especially < 2.5 μm (PM2.5) induces an increase of lung cancer, morbidity and cardiopulmonary mortality [e.g. 29-35]. Thus air pollution appears to have an adverse effect on respiratory and cardiovascular systems [36], which might result in an acute reduction of lung function, aggravation of asthma, increased risk of pneumonia in the elderly, low birth weight and high death rates in newborns [37].

Changes of Permanent Lake Surfaces, and Their Consequences for Dust Aerosols and Air Quality: The Hamoun Lakes of the Sistan Area, Iran 165

information regarding the status of dust storms and also human health and, (5) assess dust

The Sistan basin (Helmand basin) lies between the Hindu Kush Mountains in Afghanistan and the mountain ranges flanking the eastern border of Iran and is the depository that receives the discharge of the Helmand (Hirmand) river in the lower Sistan Basin (Fig. 1). It is a large and remote desert basin**,** extremely arid and known for its windstorms, extreme floods and droughts. The closed basin receives the waters of the Helmand river, the only major perennial river in western Asia between the Tigris-Euphrates and Indus rivers [9]. The Helmand and its tributary streams drain the southern Hindu Kush Mountains of Afghanistan and flow into an otherwise waterless basin of gravel plains and sandy tracts before terminating in Sistan (also Seistan, British spelling), a depression containing the large inland delta of the Helmand river

and a series of shallow, semi-connected playas at the western edge of the basin (Fig. 1).

**Figure 1.** Landsat-5 image showing the lower Hirmand Basin and Sistan region. [9].

In 1949 the United States initiated a new program for the improvement of underdeveloped areas of the world. The damming of the Helmand river in southern Afghanistan became one of the showcase projects of U.S. foreign aid in the "Third World" after World War II. Dams were built on the Helmand river and its main tributary (Arghandab river) during the 1950s. The main project goals were to provide hydroelectric power and increase agricultural productivity through irrigation and land reclamation. The Arghandab dam, located northwest of the city of Kandahar, was completed in 1952 with a height of 145 feet (44.2 meters) and storage capacity of 388,000 acre-feet (478.6 million cubic meters). The larger Kajakai dam on the Helmand was completed a year later with a height of 300 feet (91.4 meters) and length of 919 feet (280 meters) and storage

concentrations and air quality of the regions affected by the dust storms.

**2. Sistan region** 

Some dust contaminants (soluble and chelatable metallic salts, pesticides, etc) affect human health when they are transported over densely populated areas [38], retained in residences and other occupied structures [39], and they also impact the nutrient loading of waters flowing from adjacent watersheds [40] and terminal bodies of water by direct and indirect deposition [41-42]. PM is a complex mixture of substances suspended in to the atmosphere in solid or liquid state with different properties (e.g. variable size distribution or chemical composition amongst others) and origins (anthropogenic and natural). Owing to this mixture of substances, the chemical composition of PM may vary widely as a function of emission sources and the subsequent chemical reactions which take place in the atmosphere [43-45].The chemical mass balance is the most commonly used method for assessing PM source contributions [46], while statistical methods, such as factor analysis and multi-linear regression [47], have also produced interesting results regarding dust source identification. Elemental and mineralogical analyses have also been used to identify the source regions of dust deposited in Arctic ice caps [48] and on other depositional surfaces [49, 42].

One spectacular example of such dust effects is the Hamoun (dry) lakes in the eastern part of Iran that has attracted scientific interest during recent years, since it constitutes a major dust source region in southwest Asia, often producing intense dust storms that cover the Sistan region in eastern of Iran and the southwest of Afghanistan and Pakistan and influencing the air quality, human health and ecosystems as well as aerosol loading and climate from local to regional scales [50-52, 12]. Particles from the Hamoun dust storms might also cover farm and grasslands to result in damage to crops and fill the rivers and water channels with aeolian material. Over recent years, tens of thousands of people have suffered from respiratory diseases and asthma during months of devastating dust storms in the Sistan basin, especially in the cities of Zabol and Zahak and the surrounding villages [53]. According to the Asthma Mortality Map of Iran, the rate of asthma in Sistan is, in general, higher than in other regions [54].

The aim of this Chapter is to: (1) assess the seasonal and annual variability of dust storms that originate from the Hamoun Basin, (2) identify the amount of dust loading from the dry lakes, (3) assess the contribution of the lake beds to regional dust emissions for specific locations, (4) assess the dust chemical and mineralogical composition to provide useful information regarding the status of dust storms and also human health and, (5) assess dust concentrations and air quality of the regions affected by the dust storms.
