## 4 Discussion on Regional Dust Events
### Dust Outbreaks in Central Asia  
Dust storms are the main cause of air pollution in Central Asia, including Kazakhstan, affecting the ecology as a whole, and the health and living conditions at local levels. Dust, sand and salt storms occurring in Central Asian, Kazakhstan natural and anthropogenic deserts transport large amounts of deflated material over long distances, significantly affecting agricultural areas [122]. The drastic desiccation of the Aral Sea led to the intensive development of desertification processes in the region and the formation of a new desert, the _Aralkum_. In the last few decades, the _Aralkum_ has become the new \"hot spot\" of dust and salt storms in the region. Dust storms and their source areas have been determined and analyzed by satellite data. An analysis of the land-cover changes in the dried bottom of the Aral Sea revealed that the northeastern part of the _Aralkum_ Desert is one of the most active dust sources in the region, responsible for high aerosol concentrations in the atmosphere particularly in spring [123; 124]. The dust source areas are identified as the Iraq-Saudi Arabia boundary region and (recently) the northwest of Iraq, using MODIS deep blue aerosol optical depth data. Subsequently, a lagged correlation was implemented between identified dust sources and whole West Asia to determine the main paths and receptors of intense dust storms. Accordingly, southwest of Iran and Persian Gulf countries were determined as main receptors of summertime dust storms in West Asia. During spring, dust storms mostly hit the northern half of the region and reach to the Caspian Sea. Analyzing atmospheric patterns, _Shamal_ (northwesterly wind over the Middle East area) and Frontal patterns were found as dominant atmospheric circulations simultaneous with summertime and springtime dust storms, respectively [125]. In this region, a specific work described in a recent study [126] analyzed the impact of a change in horizontal distribution of emissions that lead to better simulations of dust storms with the WRF-chem model. Several studies focusing over India and Nepal agree to show the significant influence of long-range transport of dust from western desert regions, such as North Africa and the Arabic Peninsula in February-March due to changes in meteorological condition related to the starting of the Monsoon Season [127; 128; 129]. To our knowledge, the March 2014 dust episodes identified in our study were not reported in the scientific literature. Figure 22 shows a qualitative comparison between CALIOP-CALIPSO data and CHIMERE along the satellite passes. On 16 March, the pattern over the Arabian Peninsula is rather well reproduced by CHIMERE, the observed \"dust marine\" concentrations above the marine boundary layer is reproduced by the model between 10\({}^{\circ}\) N and 15\({}^{\circ}\) N in latitude. On 18 March, the satellite flies over the same regions but slightly more on the east. The two main hot spots over the Arabian Peninsula and Iran are again very well reproduced by CHIMERE, above 45\({}^{\circ}\) N the presence of clouds makes difficult the comparisons. On 18 March, the satellite passes west of Tehran (about 35\({}^{\circ}\) N) where high dust concentrations are modeled by CHIMERE, and over the west coast of the Caspian Sea with concentration peaks located above the boundary layer. The pattern simulated around 45\({}^{\circ}\) N located in the northwest of the Caspian Sea cannot be evaluated by CALIOP data due to the presence of clouds, it corresponds to a very emissive zone over the Volga delta, a large agricultural area (see Figure 3) where wind gusts exceeding 70 km h\({}^{-1}\) have been recorded.