One of the causes of atmospheric air pollution is the processes associated with its circulation, that is, the movement of air masses. Tashkent is located in the foothill zone, near the valley. Winds from the northeast and southwest play an important role in this region. The direction and speed of the wind directly affect air exchange and the dispersion of pollutants in the atmosphere.
Uzbek scientists have conducted large-scale studies aimed at studying the features of surface air circulation in Central Asia. According to the modern scientific classification, there are 17 types of synoptic processes in the region. Depending on the location of the areas of high and low atmospheric pressure, air flows move in certain directions during each type of synoptic process.
In the cold half of the year, the frequency of recurrence and duration of synoptic processes increase, accompanied by a decrease in wind speed. In such conditions, a slowdown in air exchange can be observed not only in Tashkent, but also throughout Central Asia. As a result, pollutants dissipate more slowly, stay longer in the atmosphere and accumulate in the surface air layer.
In addition, in Tashkent, as in other large cities, there are phenomena of temperature inversion. They occur especially often in winter, during periods of severe cold weather, mainly at night. At the same time, a warmer air layer is located above the cold surface air layer. As a result, vertical air mixing is limited, which contributes to the accumulation of pollutants near the earth's surface.
Synoptic processes in the atmosphere are divided into several groups. One of them is related to the passage of cyclones. Such processes are also observed in the cold half of the year. During this period, warm and cold atmospheric fronts usually pass through the territory of Central Asia, including Tashkent. They can bring precipitation, which helps to wash out some of the pollutants from the atmosphere and, as a result, improve air quality.
Another important group consists of anticyclonal processes. Within this group, there are three main types of synoptic processes. When an anticyclone is located in the European part of Russia, air flows enter Tashkent from the northwest through the territory of Kazakhstan. If the anticyclone is located in the north of Kazakhstan, the air masses move towards Tashkent from the north, also through the territory of Kazakhstan. When an anticyclone is located over Siberia, air flows enter Tashkent from the northeast through the territory of Kazakhstan. Along with these processes, areas of high and low atmospheric pressure with a small pressure gradient are observed. Windless weather or very weak wind may occur under the influence of a high-pressure area. At low pressure, calm or light wind is also possible. In such conditions, air exchange slows down, and the dispersion of pollutants becomes more difficult.
According to statistical data in recent years, there has been a tendency to increase the frequency and duration of anticyclonal processes, in particular periods characterized by the presence of areas of high and low pressure with a small pressure gradient. In such conditions, a decrease in wind speed and a slowdown in air exchange create prerequisites for increased air pollution.
Especially in winter, the frequent occurrence of temperature inversions at night can lead to the accumulation of pollutants in the surface layer of the atmosphere. Therefore, when assessing air quality, it is important to take into account not only sources of pollution, but also meteorological factors, including wind speed and direction, atmospheric pressure, movement of cyclones and anticyclones, precipitation and temperature inversions.
An in-depth study of the causes of atmospheric air pollution and an objective assessment of the impact of these factors make it possible to develop scientifically sound solutions, effectively plan environmental protection measures and take measures to improve atmospheric air quality.
