Temporal and spatial variations of particulate matter and gaseous pollutants in the urban area of Tehran

Being hemmed in on two sides by high mountains, the urban area of Tehran is characterized by high levels of particulate matter and gaseous pollutants, which have adverse consequences on human health, ecosystems and environment. Using air quality measurements taken in different regions of Tehran, spatial and temporal variations of particulate matter and gaseous pollutants are analyzed to identify the typical climatological aspects of air pollutants. In terms of particulate matter concentrations, South Tehran is more polluted than Central to North Tehran, while West Tehran is more polluted than the East. Concentrations of particles in North Tehran are lower in the midday compared to the midnight, whereas the opposite is true in South Tehran. The observed annual mean concentrations of PM2.5 and PM10 in North Tehran were 37.5 and 76.3 μg m−3, respectively, which are substantially greater than the national annual mean safety limits of 10 μg m−3 for PM2.5 and 20 μg m−3 for PM10. The observed high levels of particulate matter underline the essential need for a coordinated action to reduce the rapidly increasing air pollution over the growing urban area of Tehran. Noticeable monthly (seasonal) variations are evident in the observed PM10 concentrations, with a minimum of 61.5 μg m−3 in March (spring) and a maximum of 82.9 μg m−3 in July (summer), reflecting contribution of weather conditions. Analyzing daily PM2.5 (PM10) concentrations indicate that mid-week Wednesdays (Mondays) are the most polluted days. The higher mid-week concentrations reflect contribution of heavy vehicular traffic, industrial operation and increased commercial activities. Strong diurnal variations in the concentrations of particulate matter in North Tehran are detected, varying from a peak in late night to a minimum in late afternoon, indicating contribution of deeper daytime convective boundary layer and stronger winds in dispersion of particles.