Tehran is one of the polluted cities in the world. Despite the effective acts of the city authorities there is not yet sign of improvement. Because the main factor, that is, the PRESSURE distribution is not considered. This research is undertaken to analyze the relation between the PRESSURE changes and the pollution concentration of Tehran and identify the effective PRESSURE patterns. For this purpose the polluted days of Tehran according to CO, NO2, SO2, and TSP were extracted from the daily pollution data of Villa station, located in the central part of Tehran, during 1984-2001 period. The NCEP 00 GMT daily PRESSURE data of the pollution days at 2.5 degrees apart grid points within the 20°N to 47.5°N and 35°E to 67.5°E window were used.
Through the use of Principal Component Analysis and Clustering methods the PRESSURE distribution of pollution days were classified into six groups and then the composite PRESSURE pattern of each group was mapped. Each composite map was assigned as a weather type. These weather types are as: Northwestern Anticyclone, Caspian Low, Siberian Anticyclone, Western Anticyclone, Khorasan Low, and the Zonal type. Most of the types were frequent in fall. The Khorasan Low is the dominant type during the short period pollution runs whereas the Zonal type is dominant during longer pollution episodes.
The relation between the PRESSURE changes and the pollution concentrations were studied through the use of the daily PRESSURE of the Mehrabad station and pollution values of Villa station. The results showed positive relation between the Mehrabad grid point PRESSURE and pollution concentration of CO, NO2, and SO2, but negative relation with the concentration of TSP.