عنوان مقاله [English]
In recent years, the dust storm has been caused extensive economic, health and environmental damages. Dust storms are lower atmosphere events that result from wind erosion liberating sediment participles from the ground surface. Sand storms occur relatively close to the ground surface, but finer dust particles may be lifted kilometers high into the atmosphere, where strong winds transport them long distances. Increasing Dust storm events have several negative effects on the environment. Airborne dust causes or aggravates human health problems. Chronic exposure to fine particulates is associated with premature death due to cardiovascular and respiratory disease, lung cancer, and acute lower respiratory infections. Inhalation of fine dust particles exposes individuals not only to hazardous fine mineral particulates, but also to harmful combinations of pollutants, spores, bacteria, fungi, and potential allergens carried along with mineral dust. Poor visibility, sand movement and deposition as a result of SDS also increase incidences of road accidents and aviation hazards.
For these reasons, enough knowledge about the origin and occurrence time of dust storms could be effective in its damage reduction. The main objective of this research was the source identification of Karaj dust storm events directionally. For this purpose, Dust events in about two decades (2000-2018) were extracted from meteorological data of Karaj synoptic station. PM10 data from Karaj air quality monitoring stations and MODIS Aerosol Product were used to verify dust events that were determined in the previous step based on availability. The MODIS Aerosol Product monitors the ambient aerosol optical thickness over the oceans globally and over the continents. Furthermore, the aerosol size distribution is derived over the oceans, and the aerosol type is derived over the continents. CPF and DRS diagrams and HYSPLIT model were applied for source identification. The Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HYSPLIT) is a computer model that is used to compute air parcel trajectories to determine how far and in what direction a parcel of air, and subsequently air pollutants, will travel. HYSPLIT is also capable of calculating air pollutant dispersion, chemical transformation, and deposition. The model derives its name from the usage of both Lagrangian and Eulerian approaches. The Conditional Probability Function (CPF) calculates the probability that a source is located within a particular wind direction sector CPF is useful in determining the direction of a source from a receptor site. The DRS approach, the ratio of the concentration contribution weighted-wind sector abundance to the overall wind abundance in a wind sector is used to assess the pollution potential of the source in that sector.
Based on meteorological data and considering AOD images, the maximum and minimum numbers of the dust storm in the year had been recorded in 2008 and 2000, respectively. Also, the most dust storm occurred in summer. The most frequent dust storms were observed from April to August. Among these months, June has the most frequency of dust storms. The dust storm events increase from the beginning of the warm-season and reduce in fall when the wet and cold season starts.
Results of windrose, CPF, windrose of dust events and DRS showed the important direction in dust events of Karaj were NWW, NW. HYSPLIT results for 72 h back trajectory and dust events of Karaj in three altitudes above ground level (10, 500 and 1000 m) showed the dust origin in NW and W of Karaj had the most share on Karaj dust storm events. For example, two dust events results were presented. One of them belongs to local dust events and another for regional dust events. The results helped to identify the most important dust event origins. In overall, the results of directional source identification of Karaj dust storm showed the sources that are located in W of Karaj (in local events) and IRAQ and the north of Saudi Arabia (in regional events) have important role to increase particulate matters (PM) and decrease air quality of Karaj. In addition the results of investigation of MODIS Images for studied dust events that were the real snapshot of the earth showed the results of HYSPLIT is reliable to determine the dust storm sources. For example in 2014/4/13, MODIS image showed the source of this event was from north of Saudi Arabia and the passed above SW border of IRAN and the arrived to Karaj. This event have long journey more than 1000 km and showed the importance of dust origin that are located in other countries to air quality of Karaj. In conclusion, directional source identification of dust storm was successfully and very rapid method to understand the most important sources in any events. This methodology can be used in other studies that have concern about source identification for dust storm.