Study on the Status of SO2 in the Tehran- Iran

An air quality analysis for Tehran, the capital city of Iran, is conducted for SO₂, with the measurements taken from 1995 to 2002. Measurements were taken from the seven main monitoring stations in different locations of the city. These stations are controlled by Department of Environment of Iran. As a first step; annual, seasonal and diurnal variations were studied. The yearly variation does not show any specific trend initially but in the recent years it seems there is a little upward trend. The pick of concentration of SO₂ can be seen during 6-12 hour and during the winter season especially in January. The main purpose of this study is to see the effect of the meteorological parameters on the concentration of pollutant. For this purpose, the wind velocity, relative humidity, temperature, dew point, wind direction and rainfall are considered as independent variables. The relation between concentration of pollutant and meteorological parameters can be expressed by one linear regression equation. It is obvious from the equation that the wind speed, daily temperature and humidity have reverse effect on the concentration of SO₂. To plan and execute air pollution control programs, one must predict the ambient air concentrations that will result from any planned set of emissions. For this purpose, a two-dimensional atmospheric diffusion model for ambient air concentration of SO₂ was considered. Geostrophic winds, surface roughness, mixing height of the atmosphere, emission rate of the pollutant sources and background pollutant concentration have been taken as the input parameters. The airspace over the city to the mixing height was divided into multiple cells. Conservation of mass equations for each cell were solved for slightly stable and highly stable atmospheric conditions of city. The results of this equation were adjusted by the actual data (taken from monitoring stations).Then the modified dispersion equation for concentration of SO₂ in Tehran has been suggested. @JASEM