Destinations Frequently Impacted by Dust Storms Originating from Southwest Iran

Deserts can be considered as one of the main sources of dust emissions as they are highly vulnerable to wind erosion, i.e. The lack of vegetative cover, as well as low soil wetness, contribute to the release of particles by wind erosion. The present study examines the seasonal variation in sand and dust storms (SDSs) originating from war-impacted semi-arid bare lands affected by chemical warfare located in southwest Iran for the period of 20072018. It employs a synthesis of satellite observations and Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model trajectories. A regression analysis between annual/seasonal absorbing aerosol index distribution and selected parameters indicated strong correlation with surface skin temperature, topsoil layer wetness, and 10-m wind speed. During both cold and warm periods, Kuwait and the Persian Gulf were highly vulnerable to episodic dust incursions as they were identified in the maximum impact zone (frequency of 100%). The Persian Gulf was affected by about 12% of the total air masses during the warm period, which increased to 74% during the cold period. Regarding the vulnerability to the high wind of war-impacted regions presumably contaminated with potentially toxic elements (PTEs) and toxic compounds, the particles of contaminated dust may have been continuously transported over by the strong winds, not only the surrounding region but also long distances including agricultural land and marine environment. The study area would possibly pose a danger to the environment and human health; therefore, a detailed site characterization to investigate the degree of contamination with PTEs and toxic compounds is warranted.


Introduction
Regional and long-range transportation of mineral dust is an essential component of the atmospheric circulation. It is caused by wind erosion and transported from a local scale to a global scale by air systems. Sand and dust storms (SDSs), which are the significant sources of airborne dust, are recognized as common phenomena originating from global deserts, and they cause serious adverse human health, climate, environmental, and economic impacts (Ginoux, et al., 2012;Goudie, 2014). Accordingly, research on sand and dust cycles and routes are needed for specific issues concerning human health, weather, climate change, ecosystems, and air quality.
The primary SDS origins over the globe are located around arid regions, which are typically found on alluvial sedimentation basins at lower elevations with annual precipitation <200 mm, and with limited vegetation cover (Ginoux et al., 2012;Prospero et al., 2002). The most generative areas are detected in the north of Aral and Turkmenistan basins, the southern and eastern parts of Arabian Peninsula, the Syria-Iraqi desert, the Oman desert, and some closed inland areas of the Iranian plateau (such as Sistan Basin, Hamoun Jaz-Mourian Lake, Kavir and Lut deserts). The Middle East region and the Arabian Peninsula are responsible for releasing significant amounts of dust mainly transported over the Arabian Sea with substantial intensity from June to August (Prijith et al., 2013). Previous studies also showed that about 65% of the southwest Asian arid terrain has the potential to become a dust origin (Ginoux et al., 2012;Prospero et al., 2002). Although the Thar, Iraqi, and Arabian deserts are primary dust origins in South Asia, a small area (Sistan basin) with dried lakes (Hamoun) at the Iran-Afghanistan borders may also have a significant role (Karimi et al., 2012;Maghrabi et al., 2011;Prospero et al., 2002;Rashki et al., 2015Rashki et al., , 2013. Furthermore, researchers showed the southwest Iran (Khuzestan Province) turning into one of the significant sand and J o u r n a l P r e -p r o o f Journal Pre-proof Also, Rashki et al. (2015) pointed out some supporting evidence that the Sistan dust storms influence some parts of the Arabian Sea, controlling the aerosol optical depth evolution over the marine environment. Dust deposition over the Arabian Sea can cool the ocean surface, influence the phytoplankton, and affect the chlorophyll blooming (Rashki et al., 2015;Singh et al., 2008). Likewise, mineral dust has been suspected to be one of the most critical health risk factors for pulmonary diseases including asthma and allergies in young as well as older adults and contributes to meningitis in Sistan province of Iran (Goudarzi et al., 2018;Merrifield et al., 2013;Miri et al., 2007;Mohammadi et al., 2015;Naimabadi et al., 2016) and in West Africa (Martiny and Chiapello, 2013). While fossil fuel combustion, traffic emissions, upwind petroleum industry, and gas and oil drilling activities are the primary contributing anthropogenic sources in the Middle East, the war remains can be added to the list for southwest Iran, Iraq, and Syria. There exist some previous studies examining the SDS storms originating from southwest Iran (Shalamcheh region, (30° 45'N and 48° 15'E)), which is a war-impacted SDS source area (Broomandi et al., 2018(Broomandi et al., , 2017a. One of the critical anthropogenic origins of enriched trace elements in this area attributed to the remains of the Iraq-Iran war (Broomandi, et al., 2017). For example, the high levels of Cl and S in this area were attributed to the use of mustard gas in Iraq-Iran war during 1980-1988, andBr, Mo, Zn, and Hg were other highly enriched trace elements detected in this war-impacted area (Broomandi et al., 2017a). The presence of Pb, Cu, Hg, Br, Mo, and Zn in contaminated soils has previously been attributed to war activities (Wallace, 2018). Due to a higher level of health risk exposure, The Hg contamination in the Shalamcheh region represents a significant concern as it could be washed out by atmospheric precipitation, potentially leading to regional underground water contamination (Broomandi et al., 2017a;Wallace, 2018).
A long-term analysis of the occurrence of dust storms still lacks over southwest Asia, including the Shalamcheh region, due to the limitations of satellite imagery at the regional scale (Rashki et al., 2015). The identification of SDS pathways and origins uses specific techniques including satellite remote sensing, ground-based observations, trajectory analysis, and integrated approaches (Ashrafi et al., 2014;Broomandi et al., 2018;Rashki et al., 2015;Shao et al., 2011;Sorek-Hamer et al., 2013) and it is a significant challenge to perform in some areas of the Middle East due to certain limitations including the reliability and availability of data. Recently, the development of Global Dust Detection Index (GDDI) model (Karimi et al., 2012) and the new Middle East Dust Index (MEDI) had a significant contribution in the identification of SDS sources in the Middle East (Samadi et al., 2014).
The employment of the satellite images for monitoring SDS events is an appropriate method that is time-saving and cost-effective; however, some ground sensors with systematic xerography are needed in continuous monitoring of the surfaces covered by dust during storms (Ekhtesasi and Gohari, 2012). To the best of our knowledge, there exists no study examining the common dust transport pathways and impact zones over the region originated by the Shalamcheh during SDS events.
The current research aims to assess the seasonal formation (during the cold and warm periods) and the prevalence of SDSs originated from southwest Iran (Shalamcheh region) under specific metrological conditions (e.g., wind speeds >20 knots (kn, 1 kn = 1.852 km.h -1 ), horizontal visibility <1000 m) during 2007-2018. By providing quantitative measures, it aims to conclude whether the region can be listed among potential global sources of SDS and further assesses the long-range transport pathways and possible deposition and exposure concentration impacts of identified SDSs over the area by identifying its impact zones.

Material and Methods
J o u r n a l P r e -p r o o f Journal Pre-proof

Study area
The study area, Shalamcheh, is in southwest Iran in Khuzestan province (30°45' N and 48°15' E) (Figure 1). The area is bare land that has been affected by chemical warfare, mainly mustard gas, during the Iraq-Iran War between 1980 and 1988 (Broomandi et al., 2017a). There are two seasons in the region; the warm period is from April to September, and the cold period is from October to March. During warm and cold periods, the average received rainfall values were 17.5 ± 1.9 mm and 130.2 ± 60.6 mm; the average maximum temperature values were 46.1 ± 1.1 °C and 30.3 ± 1.1 °C, and the average relative humidity values were 32.5 ± 4.8 %, and 62.0 ± 4.6 %, respectively (Broomandi et al., 2017a). Iran. The solid red star indicates the study area (Shalamcheh). The solid red triangle represents the location of the Abadan and Khorramshahr meteorological station (ABKH).

Satellite data, trajectory, and dispersion modelling
Ozone Monitoring Instrument (OMI) absorbing aerosol index (AAI) database (http://giovanni.sci.gsfc.nasa.gov) was used (a) to evaluate the regional aerosol loads in the atmosphere and (b) to investigate the role of surface skin temperature and topsoil layer moisture in dust generation mechanism during 12 years (between 2007 and 2018). Monthly averaged AAI values at the spatial resolution of 1° × 1°, daily surface skin temperature (the mean temperature of earth's surface) at the spatial resolution of 0.25° × 0.25°, and topsoil layer moistures ( the averaged value of water content in depth of 0-10 cm underground) at the spatial resolution of 0.5° × 0.625° were used. All meteorological parameters including wind speed and horizontal visibility were daily averaged (24 hour based measurements) and taken from Abadan and Khoramshahr metrological station (30°.21′N, 48°.13′E), which is the nearest station to the Shalamcheh (Ahvaz IRIMO, 2016).
The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model is for trajectory, dispersion, and deposition calculations employing the Global Forecast System (GFS) meteorological forecast parameters of the Global Data Assimilation System (GDAS) as its initial background field. Using particle or puff approaches, it calculates trajectories as well as dispersion and deposition simulations (Ashrafi et al., 2014;Lu et al., 2018). The trajectory computation in any Lagrangian model is based on the meteorological data (U, V, and W), which has been interpolated to the grids of the model. The trajectory simulations in the present study were forwards and backwards moving from and to the dust source (30° 45' N and 48°15' E). They were run based on episodic events as suggested by de Villiers and van Heerden (2011) where a storm is classified either as sand and dust storm (e.g. 10-m wind speed >20 kn with visibility <1000 m) or severe sand and dust storm (e.g., the 10-m wind speed >30 kn with visibility <200 meters). The trajectories started at the height of one half of the mixed boundary layer. The height of mixing boundary layer and its mid-level were calculated by the HYSPLIT model and could be automatically selected using the method options (Draxler and Hess, 1997). Table 1 summarizes the monthly frequency of the identified sand and dust storms during the study period.

Sand and dust storm & severe sand and dust storm occurrences in Shalamcheh
The mean values for OMI AAI data were calculated from the daily absorbing aerosol index records for the study area. Typically, AAI values are ranging from a minimum of 0 to a maximum of 40 where higher numbers (e.g. >20) may indicate episodic atmospheric aerosol loads from dust storms or smoke emissions during the satellite scans. The daily average concentrations of absorbing aerosols are high during the warm period and especially in May, June, and July (with the highest value 27 in June); they can be attributed to mineral dust origins since no significant anthropogenic dust generation mechanisms are available in the region during the summertime. The average AAI as dust activity indicator during four months (April to July) was >20 which is close to the dust activities of primary global dust sources in the Middle East region (Arabia (southern Oman/Saudi border) with AAI values >21 and J o u r n a l P r e -p r o o f Journal Pre-proof average annual rainfall <100 mm (Goudie and Middleton, 2006;Shepherd et al., 2016). There is much less dust activity in the study area (especially in January) during the cold period.
In addition to AAI data, wind and visibility data from ground-level measurements were also screened using the criterion 10-m wind speed >20 kn, and all the potential events have been identified. The wind speeds are generally high during the warm period, especially in May, June, and July. Finally, sand and dust storm & severe sand and dust storm occasions were verified by comparing the identified events with the matching daily AAI data. Table 1 summarizes the monthly frequencies of the storms for the study region. The total number of the sand and dust storms (severe sand and dust storms) were 79 (13) in total (61 (8)  Apart from the surface wind speed, other parameters are also affecting the occurrence of sand and dust storms. For example, the topsoil layer wetness is an essential factor in sand and dust emission potential, and it can be characterized by a combination of topsoil layer wetness and surface skin temperature using satellite data. It is well associated with soil texture and aggregate stability, aggregates size distribution, and soil organic matter content; it increases the strength of inter-particle bonds by developing a sticky film between particles (Aimar et al., 2012;Broomandi et al., 2017a;Liu et al., 2012). The topsoil layer wetness has high variability both in temporal and spatial scales. The wind emission prevails by the real wetness of the first top -centimeters of soil layer (Aimar et al., 2012).
The topsoil layer wetness and surface skin temperature from OMI have been studied to evaluate the impact of the topsoil layer wetness on the dust generation mechanism. The daily averages of the surface skin temperature experienced a considerable increase during the J o u r n a l P r e -p r o o f Journal Pre-proof warm period, particularly in June, July, and August (with the highest value of 317.7 °K in July). The topsoil layer wetness had a notable reduction during the warm period, particularly from June to September (with the minimum value of 2 in September). The study on the changes in topsoil wetness and surface skin temperature showed that the minimum value of wetness and maximum value of surface skin temperature were not recorded in June, whereas the highest wind speeds were experienced in June, confirming the critical role of 10-m wind speed in generating sand and dust storms. Table 1. Monthly prevalence of dust storms (10-m wind speed >20 knots (kn)) and severe dust storms (10-m wind speed >30 kn) in the study area between 2007-2018 ("number of severe sand and dust storms" (in bold)/"number of sand and dust storms." A regression analysis was applied to the retrieved data from satellite and ground-  Namdari et al., 2018;Shafiee et al., 2016aShafiee et al., , 2016bSingh and Oh, 2007). Previous studies indicated that any increase in ambient air temperature causes a reduction in relative humidity, leading to a decrease in threshold wind speed to initiate dust emissions. Since previous studies confirmed that rainfall and temperature are two meteorological parameters which indirectly change the threshold friction velocity and directly determine topsoil layer wetness, further investigation of multivariable regression analysis by applying more parameters (temperature, rainfall, relative humidity) is recommended.
J o u r n a l P r e -p r o o f  Warm period e J o u r n a l P r e -p r o o f

Trajectory analysis in combination with AAI, topsoil layer wetness, and surface skin temperature data
The trajectory analysis was employed as a tool to assess the regional and long-range travel of the air parcels over the region for the identified events and episodes (numbers given in Table 1 did not follow the same discussed above-mentioned pattern as others did. For the time frame studied in the present research, during the warm period, the topsoil layer wetness varied between 0.14 ± 0.09 (2011)

J o u r n a l P r e -p r o o f
The forward trajectories have been started at mid-atmospheric boundary layer (ABL) in order to capture its behavior under the ABL since the air-mass altitude in the dust lifecycle has vital roles within the ABL (Cavazos-Guerra and Todd, 2012; Meloni et al., 2008;Rashki et al., 2015). It interacts with the atmospheric dynamics by influencing the heating process under ABL and the dust deposition processes at ground level (Gautam et al., 2013;Kaskaoutis et al., 2012;Rashki et al., 2015). Generally, the air-mass forward pathways were similar in the cold and warm periods. The most significant difference was the observed higher numbers of events during the warm period, e.g., 22 sand and dust storms (three severe sand and dust storms) have been observed in June, and 12 sand and dust storms (one severe sand and dust storm) have been observed in July. The warm season trajectories also reached longer destinations along with broader spatial coverage, especially in July. During the warm period, the dust-loaded air masses moved northwards, reaching Iraq, Turkey, Azerbaijan, Armenia, Georgia, Russia, and then turning toward northeastwards and affecting Afghanistan, Turkmenistan, Uzbekistan, Kazakhstan, Kyrgyzstan, Mongolia, and China. The areas within the impact zone furthermore included Jordan, Israel, Lebanon, and Syria. Air masses during these episodic events also moved to south and west, reaching Saudi Arabia, Emirates, Bahrain, Qatar, Yemen, Oman, Egypt, Eritrea, Sudan, Somalia, and Ethiopia. These systems also shifted southeastwards, affecting Pakistan and India ( Figure 6).
Kuwait was highly vulnerable to dust-loaded air systems and was located within the J o u r n a l P r e -p r o o f maximum impact zone. Saudi Arabia, Iraq, Bahrain, Qatar, Emirates, Yemen, Oman, Syria, Jordan, Turkey, Azerbaijan, Armenia, and Turkmenistan were in the medium-impact zone.
Finally, the dust-loaded air systems did hit not only the terrestrial environment but also the marine environment such as the Persian Gulf (frequency of 100%); Caspian Sea, Arabian

Regional transport pathways
Although the frequency maps are quite informative tools to assess the potential impacts zones, they do not provide a clear idea of the main transport pathways. Therefore, the HYSPLIT-4 clustering algorithm was used to identify the main routes of the identified episodes. This method clusters all the provided trajectories utilizing the change in the total spatial variance (TSV) parameter to determine the optimum number of clusters (Lu et al., 2018), and it has been used for the sand and dust storm events of the warm and cold periods during 2007-2018. The trajectory cluster groups, along with their frequencies for the warm and cold periods, are presented in Figure 8. During the warm period, the most frequent J o u r n a l P r e -p r o o f receptors of the air masses carrying dust particles were Saudi Arabia, Iraq, Yemen, Oman, Kyrgyzstan, and Emirates (12%, 12%, 20%, 21%, and 2%, respectively). In the cold period, the most frequent receptor of the air masses carrying dust particles was Iraq (17%). In this time frame, local areas (Iran) also received dust particles (8%). Besides the terrestrial receptors, some marine environments were other main hosts for the air masses carrying dust particles originated or enriched from Shalamcheh: During the warm period, the Persian Gulf and Arabian sea were affected (12% and 20%, respectively). During the cold period, the Persian Gulf was the most frequent marine receptor of air masses (74%).

Dust deposition and potential impacts
It should be stated that the following discussion has been constructed based on the information from the literature and its relation to our findings thus are hypothetical. The results from the present study do not provide direct evidence on the environmental and health impacts on receptors since this study does not include any analysis in the receptor points and areas.

J o u r n a l P r e -p r o o f
The long-range transport of windblown dust occurs with high temporal and spatial variability influenced by wet and dry deposition processes (Mahowald et al., 2017;Zhang et al., 2018;Zheng et al., 2016) and this could be experienced across continents and oceans, causing concerns in both terrestrial and marine ecosystems (Kok et al., 2017;Zhang et al., 2018) with levels exceeding 100 g.m −2 deposition per year. Mineral dust particles contain macronutrients (such as silica and phosphate) and micronutrients (such as zinc and iron), which can enrich both terrestrial and marine ecosystems (Kohfeld and Tegen, 2007). For example, in marine environments, the long-range transport and subsequent deposition of dust aerosols can stimulate the growth of certain aquatic organisms due to the influx of nutrients as well as sequestrate carbon in the deep sea (Molloy and Mihaltcheva, 2013). Besides, dust particles by carrying the carbonates, are important sources of carbon for the alkaline carbon pool, capable of buffering the acidity of atmosphere and increasing the alkalinity of seawater, hence influencing large-scale environmental and climatic changes. As a result, while sand and dust storms (SDS) events can impact the atmosphere, they can reduce the acid deposition from the atmosphere and help the mitigation of global warming (Wang et al., 2017).
In the present study, the Persian Gulf could be the primary chronically affected marine ecosystem by the dust aerosol originated from Shalamcheh. The Persian Gulf (relatively shallow with a mean depth of 35 m) is located between Iran and the Arabian Peninsula. It is a semi-enclosed body of water that is only connected to the open waters through Hormuz Strait (Freije, 2015). It includes a variety of relatively sensitive ecosystems that are associated with an environment that is naturally under high stress and with poor flushing characteristics, very high evaporation rates, UV exposure, salinity, and elevated temperatures. Thus, contaminants are subject to a slower dispersion, limited dilution, and thus remain in the system for more extended times (de Mora et al., 2004;Freije, 2015). The seafood from the Persian Gulf (including fish and shrimp) is valuable and is subject to both J o u r n a l P r e -p r o o f Journal Pre-proof local consumption and export. As a result, it is essential to maintain good marine environmental quality for environmental, social, and economic reasons (Sheppard et al., 2010). Moreover, maintaining seawater quality is vital since many of the Gulf countries depend on the desalinated gulf water as a source of potable water for both domestic and industrial uses (Freije, 2015).
The soils of Shalamcheh are mainly constituted of SiO 2 with a mean value of 29.2%, and the total Fe content (as Fe 2 O 3 ) of soil samples is 4.19% (ferric iron). SiO 2 and Fe 2 O 3 content of dust particles was 31.9% and 2.13%, respectively, over Khoramshahr city (the nearest local terrestrial receptor) (Broomandi et al., 2017a). The ferric form of Fe that is dominant in aerobic environments is less soluble and occurs primarily as insoluble precipitates. Therefore, to obtain ferric iron, many aerobic microorganisms need to produce chelating iron-binding proteins capable of exchanging soluble Fe soluble and transporting it into the cell. In marine environments, by conducting an Fe fertilization study, researchers witnessed an increase in phytoplankton growth by the rate of two to three times background values. They have also discussed the influence of aeolian Fe on marine primary productivity rates in the iron-limited waters of the North Pacific (Griffin and Kellogg, 2004).
In contrast to supplying Fe by dust deposition in marine environment, it might be crucial to consider the role of the deposited dust in the scavenging of dissolved iron. In regions with high Fe concentrations, dust deposition acts as a net sink of dissolved Fe if the scavenging removal would exceed the Fe input by dust deposition (Ye et al., 2011;Ye and Völker, 2017). Generally, dust depositions act as an Fe input comparing to lithogenic scavenging in most parts of the Atlantic, but dust deposition could act as a net sink of dissolved Fe in some areas in the western part of the subtropical North Atlantic. Interestingly, a decrease of about 3% is witnessed in the global net primary production and export production, especially in the areas with high-nutrient low-chlorophyll like equatorial Pacific J o u r n a l P r e -p r o o f Journal Pre-proof and the Southern Ocean. It shows that lithogenic scavenging can globally impact marine productivity, even if the amplitude of the total change is small (Ye and Völker, 2017).
Also, previous studies suggested a possible association among dust storms and Fe and P enrichments in oceans (Tagliabue et al., 2017). Atmospheric dust fallout could result in the deposition of more than 60 Tg Fe and 1 Tg P into the world oceans (Mahowald et al., 2017).
Also, Fe in dust aerosols may couple with anthropogenic S in the atmosphere and oceans, enhancing solubility and subsequent availability to aquatic organisms (Zhuang et al., 1992).
Besides the Persian Gulf as the probable primary chronically affected marine ecosystem, Kuwait could be the main terrestrial ecosystem chronically affected by the dust aerosol originated from Shalamcheh. Since dust particle's composition can vary from place to place due to the various origins, seasons, and weather conditions, it is critical to have a better Therefore, it can be hypothesized that one of the primary anthropogenic sources of contaminants in the area is war remains.
The EF values for selected trace and major elements from soil samples taken from Shalamcheh showed that Br, Cl, Mo, S, Zn, and Hg are of anthropogenic origin in the study area (Broomandi et al., 2017a). The war remains from Iraq-Iran could be one of the critical anthropogenic sources of trace elements in this area. Furthermore, high values of Cl and S encountered in the local soils could be attributed to chemical warfare (the use of chemical agents such as mustard gas) in the Iraq-Iran war during the period 1980-1988 (Broomandi et al., 2017a;Ghanbarizadeh and Nejad, 2012). It has been shown that the presence of Pb, Cu, Hg, Br, Mo, and Zn in contaminated soils could be linked to intense war activities (Wallace, 2018). The enriched Hg in the location may also be linked to war activities (Broomandi et al., 2017a).
Previous studies estimated possible dry deposited amounts of certain elements (Br, Mo, S, Zn, Ni, Cr, Co, and Hg) over Ahvaz city as a local receptor of dust particles originated from Shalamcheh in 2010 (Broomandi et al., 2018). Br, Mo, S, Zn and Hg identified as potential soil contaminants in the study area also had high EF values in the fallout dust particles over Ahvaz city in 2010. Their presence in Ahvaz airborne dust has been attributed to possible non-crustal sources such as fossil fuel combustion, traffic emissions, gas and J o u r n a l P r e -p r o o f drilling activities, upstream petroleum industry (in Khuzestan or neighbouring dust origin areas in Iraq and Saudi Arabia), and remains of the Iraq-Iran war (Broomandi et al., 2018).
Therefore, the Persian Gulf, as the probable primary chronically affected marine ecosystem, by the dust aerosol originated from the war impacted area of Shalamcheh can be harmful to marine organisms and their ecosystem. According to the provided data by Paytan et al. (2009), frequent sand and dust storm events act as an essential source of both marine nutrient and terrestrial contaminants to the marine environments. The high levels of heavy metals (such as Cu and Pb), the toxic organic matter (such as polyaromatic hydrocarbon), and the interaction among dust particles and the contaminants during the transport can bring harm to the marine organisms and ecosystems. Studies showed that the presence of toxic substances carried by dust particles could increase the coral mortality rate in the Caribbean Sea (Paytan et al., 2009;Wang et al., 2017).

Conclusions, Implications, and Limitations
The present research assessed the seasonal formation (cold and warm periods) and the prevalence of sand and dust storms (SDSs) originated from a potential SDS area (Shalamcheh region southwest Iran) during 2007-2018; and, assessed the long-range transport pathways along with potential impact zones. The persistence of intense dust activity (especially during the warm period) suggests that the study area is a potential dust generation source at a global scale.
It is suggested that a decrease in topsoil layer wetness during the warm period resulted in increasing concentrations of absorbing aerosol in the atmospheric column. The saltation, resuspension, and/or creeping of sand particles start with certain controlling weather conditions (e.g., wind speed and topsoil layer wetness), which are required to be at specific J o u r n a l P r e -p r o o f Journal Pre-proof thresholds based on the sand particle characteristics (e.g., size, shape, and density) of the topsoil. Following the resuspension process, they can be transported over long distances.
Overall, the results indicated that the study area acts as an SDS source in the region.
Based on the Total Zone Mapping Spectrometer data, the recorded severe and arid conditions in the area showed that it is a vulnerable dust source with a persistent average annual rainfall of under 100 mm (Goudie and Middleton, 2006) that makes the area a potential location prone to desertification. The susceptibility of the study area to turn into a permanent dust source with desertification has also been mentioned in other studies (Broomandi et al., 2017a;Cao et al., 2015;Heidarian et al., 2018). Dust-storm pathways from Sahara towards the tropical Atlantic, the Mediterranean, and the Middle East have been well documented (Awad and Mashat, 2013;Liu et al., 2012). In Iran, those originating from the Sistan basin were also examined (Rashki et al., 2015), but those originating from Shalamcheh have yet to be studied.
To the best of our knowledge, the current study is the first that examines the dust-transport pathways and the regional areas affected by the Shalamcheh sand and dust storms in full scale.
The trajectory modelling has identified long-distance receptor areas (impact zones), indicating that numerous countries, as well as marine zones, receive dust from the area (Kuwait and the Persian Gulf under particular high impact), which might significantly affect nutrient as well as potentially toxic element (PTE) profile of the environment. Regarding the high wind vulnerability of the study area, which is also a war-impacted region with a potential presence of PTEs and other toxic substances, contaminated dust particles may be transported over not only the surrounding region but also long distances, including agricultural land and marine environment. Previous studies on the Persian Gulf have already reported elevated levels of 11 trace PTEs (including Zn, As, Cr, Cu, Pb, Ni, Cd, and Hg), mainly in marine and coastal areas (Fowler et al., 2007;Freije, 2015;Juma and Al-Madany, J o u r n a l P r e -p r o o f 2008; Naser, 2009). As the study area is now identified as a source of SDS and it is at the same time a war-impacted area, potentially contaminated, it is recommended to perform site characterization studies taking major war-impacted zones into account. It is highly recommended to take effective functional stabilizing methods to control the wind erosion on susceptible regions of the study area.
One of the main limitations of the present study is the lack of on-site meteorological and air quality stations, which made the study rely on the closest available stations (Abadan and Khoramshahr meteorological stations, Khorramshahr air quality station). Also, for the time frame studied, the availability of PM 10 data, measured at Khorramshahr air quality station (the nearest station to the area of interest), was below 50% which prevented our team from performing statistical analyses to investigate the relationship between measured groundbased PM 10 and retrieved AAI data. Finally, topsoil layer wetness and surface skin temperature values have not been measured in any of the ground stations; thus, it was not possible to investigate the relationship between measured ground-based data and satelliteretrieved data.