Tracing dust sources in different atmosphere levels of tehran using hybrid single-particle lagrangian integrated trajectory (hysplit) model

The present study aims to tracing dust sources of Tehran (capital city of Iran) using HYSPLIT model and atmospheric circulation systems at different levels. The statistical analyses within the period 1981-2005 indicate that one of the most significant dust events in Tehran province occurred in May 2000 and continued for more than 4 days in Abali, Chitgar, Firuzkuh, Karaj and North Tehran stations. For this purpose, in order to identify the sources of dust particles and their directions, firstly, high-level atmospheric data including zonal and meridional wind, geopotential height at pressure level of 700 and 850 hPa and atmospheric circulation patterns were studied from two days before the storm, the first of May until the end of the second, fourth and fifth day. By using atmospheric circulation maps, the synoptic systems effective in causing dust events, flows directions and their speeds were determined. In this modeling approach, a backward particle tracking method was applied to determine the direction of dust particles, 48 hours before dust storm in Tehran, at three elevations of 100, 500 and 1000 meter. With regard to the fact that the pressure systems of northern latitudes are active over Iran in transition period of spring, it should be noted that the results of the present study were affected by these systems. Results indicate that the high-pressure system hovering above the Saudi Arabia and the low-pressure tongue at higher latitudes play an important role in forming particle motion patterns and flow speeds of mentioned levels. Using HYSPLIT Lagrangian model shows the effects of arid regions of Saudi Arabia, Iraq and some parts of Syria on producing greatest amount of dust particles transferred to Tehran.