## 4 Discussion and Conclusions  
In the present study, the WRF-Chem model simulated the dust emission flux during the storms of 14 February 2018 and 21 February 2015. The selection criterion for the storms was observed horizontal visibility of less than 1000 m, which was determined using the data of synoptic stations. In order to validate the synoptic data as well as to investigate the extent of the storms in the study area, MODIS images were used to show the dust on 14 February 2018 and 21 February 2015 in Central Iran. MODIS images confirmed the horizontal visibility observations at synoptic stations. Additionally, the NOAA HYSPLIT model showed that airmasses originating in external dust source regions affected much of central Iran. The results of back trajectories from the NOAA HYSPLIT model show that dust storms on the February 2018 and 2015 involved flow from the Arabian Desert to the Central Plateau. In this study, two schemes were used for WRF-Chem simulation. Different domains were employed for the two events to capture the dust source suggested by the back trajectory analysis. Vertical dust flux maps were simulated using the AFWA and GOCART schemes, and the output fields analyzed at 3-h intervals. The results showed that the WRF-Chem model can simulate the dust phenomenon well and is able to identify highly erodible surfaces with both schemes. This study showed that the Arabian deserts play a key role in the formation of the core of Iran's dust storms. Given that Persian Gulf is in between Iran and the Saudi Arabian deserts, one may understand that conditions are also difficult for shipping due to the reduced horizontal visibility when dust storms occur in these areas. The results also show that Loot desert and central desert are two of the main dust sources in Iran. These severe storms occurred in winter, which is the cool and rainy season of the region. However, due to climate change that is reducing rainfall in the area, wetland areas are becoming drier even during the cool and rainy season and may become a dust hot spot. Due to the significant decrease in precipitation in the study area and the severe dryness of soil surfaces, the VDF from the Loot desert reached over 4000 ug/(m\({}^{2}\)s). The results of the simulation of the storm of 21 February 2015 in the Central Plateau of Iran by the WRF-Chem model show that the central core of this phenomenon is in the Arabian deserts, along with, in south-eastern Iran, parts of Loot desert and Jazmoorian wetland, which are considered as the internal cores of this storm. Horizontal visibility of synoptic stations and surface concentration simulated by GOCART and AFWA schemes were used to validate and compare the results of the two schemes. The results showed that the values simulated by the GOCART model had a significant correlation with the values of the horizontal visibility at the synoptic stations, but the results of the AFWA model did not show as high a correlation. The number of source regions identified by the GOCART model in the storm 14 February 2018 is eight, including two sources in Loot desert, one source in Jazmourian, one source in Hirmand basin, two sources in Central desert and one source in Dranjir desert. Additionally, the number of sources identified by the GOCART model in the storm of 21 February 2015 is four with two sources in Loot desert, one source in Jazmourian and one source in Hirmand basin. Several previous studies are consistent with the result of this paper. [PERSON] et al. [67], in a study to determine dust sources in Iran, stated that in south-eastern Iran, Sistan basin can be characterized as an internal dust source. Additionally, [PERSON] et al. [34] also pointed to the importance of the Sistan basin in eastern Iran and the 120-day winds in this area, which is one of the most important causes of dust in the eastern and south-eastern regions of Iran. This is consistent with the results of this research (identification of dust centres in Hirmand Basin); [PERSON] et al.