Temperature
In the Tehran metropolitan, the annual mean temperature changes between 15 to 18 Celsius degrees and given the height differences in the city, the various parts have an average of 3 Celsius degrees difference in temperature. This difference remains almost the same in cold and warm seasons of the year.


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Figure 1.4  Changes in the mean of the minimum temperatures during cold seasons


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Figure 1.5 Changes in the mean of the maximum temperatures during warm seasons


Precipitation
The annual precipitation in Tehran is mainly affected by the height differences, varying between a maximum of 422 millimeters in the north and a minimum of 145 millimeters in the southeast. The number of rainy days follows the same pattern and varies between 89 days in the north and 33 days in the south. Also in the city area, there are about 205 to 213 days of clear sky with some clouds per year.


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Figure 1.6 Spatial changes of annual precipitation


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Figure 1.7 Spatial changes in the number of days with precipitation


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Figure 1.8 Spatial changes in the number of days with clear to cloudy weather


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Humidity
The aviation of monthly mean relative humidity include minimum and maximum relative humidity registered at Mehrabad Station shows that in mornings, humidity changes from a minimum of %38 to a maximum of %79 in July to January. The changes in the relative humidity in midday vary between %15 in June to %47 in February.

Pollution
Air pollution of Tehran is one of the major problems that the greater Tehran is faced with. With a population of 7.7 millions, Tehran is the biggest industrial and business centre of the country, and one of the great metropolises of the world. Natural factors, urban structure layout, more than 2 million active vehicles, five hundred thousand motorcycles, five thousand industrial units (25% of country’s total industries) with the 20% consumption of country’s energy, centralization of 70% of all services and 80% of all the experts has turned this city to one of the most polluted cities in the world (according to Environmental Protection Organization in 1997) which was also been referred to as the world second most polluted city, for a period of a time, New Delhi being the first.





Figure 1.9 Percentage of monthly changes of min. and max. relative humidity at Mehrabad Station

Table 1.3 Long-term average of daily temperature at selected stations in Tehran

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Table 1.4 Emission of pollution in the industrial sector (kg. per day)

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Table 1.5 Emission of pollution from commercial sources in Tehran (kg. per day)

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Table 1.6 Degree of pollution of three types of vehicles

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حق انتشار اطلاعات براى شهردارى تهران محفوظ است 1396 - 1385
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