A Study on Dust sources and Weather Patterns Associated with Sever Dust Events in Tehran Area

Iran is located in a dry and semi-dry region. Due to the climatic status of latitudes Iran is located in, most and the largest deserts exist. The conditions of land use like the kind of soil, plant coverage, soil moisture, mountain effects, water sources like contamination of surface waters, building dams and river's deviation, are factors directly contributing to the phenomenon of dust. Of main factors of creating this phenomenon are the winds blowing somehow gale-force in deserts with proper situation for making dust. These factors along with the vertical motion of the air due to atmospheric systems transfer the suspended dust particles vertically to higher levels of atmosphere. Based on their diameter, the floating particles go to different layers from bottom to top and then move with currents of air in those levels and cover a vast area. In fact, bigger particles roll by the wind in their movement while smaller ones get up from the ground by the wind's vacillators moves and move in the air. Very small particles, suspended. There are not any distinct separating lines of particle size among ways of transfer; therefore atmospheric systems have a major role in the process of creating and moving the dust. In this study, the meteorological conditions were investigated to detect the sources for the creation of dust storms which caused Tehran’s air to have a very unhealthy condition in having a high rate of suspended particles. To do this, first through the data(PSI values) from the Tehran air quality control company were determined, then the existing meteorological data like actual maps, the reanalyzed daily data from the national center of atmosphere research(NCEP/NCAR) and some detector Satellite images of the dust from 2 days before the occurrence of dust episodes, meteorological conditions and atmospheric systems were investigated and finally according to the backward trajectory technique, the approximate locations of dust sources were determined. The results show that the centers of dust creation for the worse situation happened in Tehran were in Northern Iraq and Eastern Syria. Also there are modes which show according to the situation of high persistence on the region and dominant currents of Northeast and South, it is most likely that the Iranian central deserts and the dust from human sources like construction in Southern suburban areas and inside the city have also affects, especially in clod season.