The relation between pressure and air pollution concentration in Tehran

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. It is observed that during a cyclonic day the air is much cleaner than an anticyclonic day even during week days. As a result 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. 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. The respective models were developed according to the pressure of the day (D), one day ahead (DB), two days ahead (DBB), and three days ahead (DBBB) of pollution episode. SO2=.000252*DPRESSURE-.21 SO2=.001322*DBPRESSURE-1.287 SO2=.001408*DBBPRESSURE-1.375 SO2=.001788*DBBBPRESSURE-1.762 NO2=.001401*DPRESSURE-1.352 NO2=.003335*DBPRESSURE-3.312 NO2=.002489*DBBPRESSURE-2.451 NO2=.0022*DBBBPRESSURE-2.163 CO=.101*DPRESSURE-97.016 CO=.222*DBPRESSURE-219.84 CO=.234*DBBPRESSURE-231.728 CO=.259*DBBBPRESSURE-257.689 PM=1308.063-1.183*DPRESSURE PM=5184.148-4.985*DBPRESSURE PM=5771.84-5.563*DBBPRESSURE PM=5464.97-5.261*DBBBPRESSURE

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.

Key words: Tehran, weather types, air pollution, air pollution and pressure patterns .pressure models of Tehran pollution.