Document Type : Research Paper

Authors

• Ali Ghasemi Beqtash ¹
• Ali Mohammad Khorshiddoust ²
• Khalil Valizadeh Kamran ³

¹ Ph.D. Student of the Climatology Department, University of Tabriz

² Professor of Climatology,University of Tabriz

³ Associate Professor of Remote sensing and GIS Department, University of Tabriz

Abstract

Introduction
Today, there are many factors involved in air pollution. PM₁₀ is one of the significant elements influencing air pollution in the city. Due to their fineness, these particles can travel to high altitudes and long distances. The metropolis of Tabriz is known as one of the polluted cities whose air pollution is caused by burning a huge amount of fossil fuels, lack of green space and topographic and climatic conditions. Given that the purpose of synoptic studies is to explain the key interactions between the atmosphere and the surface environment, and synoptic climatology pursues a major goal and that is to find the relationship between atmospheric circulation and the surface environment. Given the importance of the phenomenon of dusty air pollution and on the other hand its widespread spatial expansion in recent years in the northwest, the need for this research was felt more than ever; Therefore, in this study, suspended particles in the atmosphere have been analyzed as one of the most important air pollutants in Tabriz
Materials and Methods
In order to investigate the effect of active pressure patterns on pollution in Tabriz metropolis, the synoptic analysis method was used. In order to influence the meteorological conditions on increasing and decreasing pollution, pressure gauging meters have been used in connection with the main PM₁₀ pollutant. To achieve this goal, the average daily data of PM₁₀ in the years 1992-2010 in Bagh Shomal station and meteorological data of Hamidid station in Tabriz have been used. The method was as follows: the data were first entered into Excel software and based on the standard table of air quality, the standard limit of pollutants was determined. Extreme contaminated days were filtered and extracted by Excel. Polluted days with dangerous conditions on March 15-16, 2009 and to May 6 the same year. Then using the surface pressure data, the level of 500 hPa of pressure patterns on the infected far days were analyzed. The study of air quality index showed that the highest number of polluted days occurred in 2008 and the lowest number of dangerous polluted days occurred in 2006. In addition, the highest number of dangerous polluted days occurred in March, May, April and June. The results of the study of synoptic patterns show the existence of a weak pressure cells at the level of 500 and the dominance of a strong low pressure system at ground level and the distribution of temperature along with the hot core over the region. Also, the effect of the condition of the upper levels of atmosphere on the contaminated days by drawing synoptic maps of 500 hPa on the polluted days were examined.
The Lund correlation method was used to select the representative days of the groups obtained from the classification of atmospheric pressure data. In this way, to select the representative day, the day that has the most similarity with the most number of group days was selected.
Findings and Discussion
The correlation coefficient represents the degree of similarity of the patterns of the two maps with each other. To do this, a certain threshold correlation coefficient must be accepted. The value of correlation coefficient in such cases typically varies between 0.5 to 0.7. Representative days were extracted based on a threshold of 0.5. Thus, the day that has a correlation coefficient of 0.5 with more days was selected as the representative day. The 500 hPa pattern, which has changed the climate of Northwestern Iran, is a Rex-type blocking system. Such a system is called lateral lifting Rex. After re-combining the western current in the east of this system, hot and dry conditions are applied to the area under their coverage. From the Northwestern region of Iran, in the impact basin of the low eastern part of this Rex system, which is mentioned outside the combined flow; Therefore, the unstable conditions in the study area are due to the positive rotating tawny wind of this arrangement from the lateral Rex system.
In the case of west and east winds, the type of flow is important because their flow can be orbital or meridional. The wave motion of the winds in the meridional direction causes cold air to accumulate and fall inside the vessels within the higher latitudes to the lower latitudes, and vice versa, in the ridges, the warm air of the lower latitudes ascends to the higher latitudes. Orbital component maps show the direction of the wind (if the direction of the wind is negative and if it is positive in the direction of the west) and the speed of the orbital winds. The meridional component shows the wind speed in the north direction (if the wind speed values ​​are positive) and south (if the wind speed values ​​are negative). The wind map on the first day of pollution shows that the current The wind blows in a counter-clockwise direction in the low-lying center of the Mediterranean and at the same time in Northwestern Iran it moves in a counter-clockwise direction (anticyclonic) and increases pollution in the metropolis of Tabriz, but on the last day it gets west-east and The severity of pollution in Tabriz metropolis is gradually decreasing.
Conclusion
Given the importance of the phenomenon of dusty air pollution and on the other hand its widespread spatial expansion in recent years in the Northwest, the need for this research was felt more than ever; Therefore, in this study, suspended particles in the atmosphere, which is one of the most important air pollutants in Tabriz, has been analyzed. Examination of the air quality index of Bagh Shomal station in a period of study showed that the highest number of polluted days occurred in 2008 and the lowest number of dangerous polluted days occurred in 2006; but based on the persistence index and the average, days polluted with the dangerous condition of suspended particles were analyzed. According to the air quality index, the highest number of dangerously polluted days occurred in 2008 and in March, May and April. The hot core is on the area. Also, the effect of the condition of the upper levels of atmosphere was studied by drawing synoptic maps of 500 hPa on the polluted days. From the polluted middays, the two time periods of March 15 to March 17, 2008 and May 15 to May 17, 1988 were analyzed due to the continuity of the three days and the results indicated that there was a direct correlation between airborne synoptic circulation patterns and the polluted days in Tabriz. The main source of dust entering the metropolis of Tabriz during two periods with severe pollution of the deserts of Central Asia and Afghanistan. In addition this study showed that high air pressure, especially in the morning in autumn, causes an increase in the density of pollutants on the ground.

Keywords

• Dangerous pollution
• atmospheric models
• cluster analysis
• representative day؛ PM10

Main Subjects

• Climatology