Investigation of spatial and temporal distributions of air pollutants over Tehran in cold months of 2011-2013

Aims: Nowadays, air pollution has become a major problem in the populated areas such as Tehran and other large cities in Iran. In such areas, the spatial and temporal variations of air pollution are important. In this study, spatial distribution of air pollution over Tehran is considered in cold a season during acute air pollution periods while indicating the factors involved.

The air pollution data of 16 stations located throuought Tehran for the years 2011-2013 have been used to find contour maps of gaseous and particle mater pollutants using interpolation techniques of which Kriging was more appropriate.

Results of the investigations of spatial and temporal distributions of air pollutants during the acute air pollution periods which often occur in cold months over the city, showed that in December 2012 that the concentration of gasous substances increased northwards, while that of particle matter increased towards the southwest. The north-south gradients of CO are highest during the day especially in the midday, while they are reduced substantially during the night. This appears to be due to the atmospheric local circulation, mainly due to the northern mountains inducing katabatic and anabatic near surface winds during the nights and days respectively. The atmospheric boundary layer thickness (increasing southwards) seems also important in the spatial distribution. As expected, the mean vales of CO at nights are higher than those during the day because high stability conditions prevail during the nights particularly in this mountain surrounded city.

The trends of concentration of particle matters in cold month show that it first increases in the southwest and west of the city and then by local wind circulation spreads towards the other parts of the city. This is probably due to the vicinity of the southern parts of the city to the more dry lands as well as the sources of the building construction industries. Larger air pollution anomalies are also found to occur for the particle matters during acute air pollution periods in cold season.