Identification of sources of dust that influence Tehran based on the application of the MERRA-2 data

We utilized the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) data with a horizontal resolution of 0.5°×0.625° for the period 1980-2022 to identify sources of dust that influence Tehran province in different months of the year. The results indicated that surface dust mass concentration in Tehran province reach their peak levels in late spring and during summer, particularly in July. The maximum dry deposition flux in Tehran is in April and May, while the maximum wet deposition flux is in March and April. Wet deposition flux is higher in highlands and in areas where precipitation is relatively high compared to lowlands and areas with low precipitation. Dust emission flux is higher during spring and summer in Tehran compared to other seasons, with the highest values in June and July, concurrent with the maximum dust emission flux in Dasht-e Kavir. Varamin is the only region in Tehran province that contributes to extensive dust emissions. In this region, dust emission flux is higher than dust deposition flux in summer. The analysis of dust emission flux and dust surface mass concentration in Tehran during the period 1980-2022 indicates significant increasing trends in spring and summer, respectively. In this study, we also identified potential dust sources that influence the Tehran province. We examined those sources that have a high level of dust emission flux and are either located in or near Tehran or along the path of weather systems moving from the west to the east. These sources include (1) the western Middle East region; (2) Dasht-e Kavir; and (3) sources in Tehran. In all these areas, the maximum dust emission flux and surface dust mass concentration occur in late spring and during summer, particularly in June and July, while their minimum values are in autumn and early winter (October to January). Although, dust dry deposition flux shows high values in the vicinity of or near the regions with high dust emission flux, dust wet deposition flux has high values in areas with relatively high precipitation such as the Alborz and Zagros Mountains. In the western Middle East and Dasht-e Kavir, dust emission flux is higher than the sum of dry and wet deposition fluxes in all months of the year. The correlation analysis between dust emission flux in the abovementioned potential sources of dust and the surface dust mass concentration in Tehran indicates that from January to April, the western Middle East region is the main source of dust that contributes to the occurrence of dust events in Tehran. In summer and early autumn, in addition to dust sources in the western Middle East, the contribution of Dasht-e Kavir and dust sources in the Tehran province becomes significant. This explains the observed maximum dust surface mass concentration in Tehran during summer. The results of this study have important implications for better understanding potential sources of dust that influence Tehran in different months, based on which monthly variation in terms of the health and environmental impacts of dust can be obtained.