عنوان مقاله [English]
The issue of urban climate has been greatly addressed in the recent years. The migration of human beings to cities, along with the density of the residential units, the noise of urban vehicles and dangers of air pollution and many other things have had bad effects for the human beings like asthma, bronchitis, cardiovascular diseases, and skin cancer. The issue of air pollution is one of the main factors in urban climatology. The knowledge of climatology emphasizes on the effects of atmospheric pollution on the climate and vice versa. The investigation about the effects of air pollution on climate features has greatly been conducted in the east Iran. In the warm seasons of the year, especially in summer, Subtropical High pressure (STHP) covers large areas of lower, middle and upper levels of atmosphere. This extends vertically on top of the high pressure at 200 hp to 700 hp and results in a clear sky with no clouds and rain. Subtropical High Pressure (STHP) all over the country varies from one day to other day. In some areas it is very close to the earth surface, in the south east parts of Iran in some days it is about 2000 or 3000 meters above the earth surface and allows warm, low moist air. This situation sometimes spreads to northern Iran and causes monsoon rain with increase in temperature and decrease in air ascent. This means that when the height and activity of the STHP is high, there is suitable condition for clear sky and direct solar radiation. On top of the inversion water vapor content of the air is so low that it can't be measured. Subtropical system in high altitude is one of the reasons for the formation of deserts in Iran. Subtropical high is getting stronger with increasing height from the ground, while the polar high becomes weaker with increasing altitude.
As a matter of fact, mechanism for summer subtropical high pressure on Iran is a part of the Azores high pressure on the region. Thus, the above factors have caused the greatest events in the summer in Tabriz so that the city has experienced dangerous contaminants. With the beginning of autumn, the maximum and the minimum values of the dangerous contaminants was shifted compared with other seasons. However, in autumn there are dangerous infected cells in northern city of Tabriz in November and October, while in December the infected cells are in the center of Tabriz. The purpose of this study was to evaluate the frequency of Tabriz dangerous contaminants. For this purpose, the data of pm10 pollution index in the 8 years period (2005 to 2012) were evaluated by the Environmental Protection Agency in Tabriz (EPAT) for five stations of Baghshomal, RAhahan, Abrasn, Hakim Nezami, and Rastekhocheh. The index of this research is the day that the pm10 value of 420 is larger. The frequency and continuity of these dangerous days for each station were analyzed and investigated. In this study, we have used MATLAB for statistical analysis and SURFER for the mapping.
Results and discussion
The results of the analysis have indicated that there were many dangerous air pollution events in summer in all stations with more dangerous contaminants in August as the highest frequency of the occurrence of dangerous infections.
This indicates that formation of subtropical high pressure dominated on Tabriz play a key role in air pollution. However, in winter the occurrence of dangerous pollution has been reduced in most of the stations. Among the stations of this study, the stations of Baghshomal and Abrasan had the most dangerous pollution. The number of the days of infection in both stations has reached to more than 400 days during the study period. Furthermore, the results of the continuation of the dangerous contaminants of pm10 index indicate that more continuity of the pollution was in Baghshomal station and the lowest in Rahahan and Hakimnezami stations.
The spatial distribution of pollutant cells is varied in different months in Tabriz. However, based on PM10 density the dangerous pollution in most of the months has been formed in the city center. In January, February, June, September, October (multi-core) and December there were the core and the density of pollution in the city center. In March and August, the maximum contamination of Tabriz has been observed in the East. Intensity of infestation was observed only in April, July and November in west Tabriz while the maximum condensation has been observed in the northern and the southern parts of the Tabriz. Tabriz had no nuclei condensation of dangerous pollution in July.