Air Protection and Air Quality in Cities of Uzbekistan

The atmosphere (from the Greek words atmos - air and sphaira - ball) is not only the air that humans, animals and plants use to breathe, but also the gaseous envelope of our planet that protects it from sudden temperature fluctuations (without the atmosphere, daily temperature fluctuations on Earth could reach 200 °C) and protects all living organisms from harmful radiation from the Sun and space. The atmosphere is also the environment in which climate, winds and rainfall form; it is also the environment in which weather, which plays an important role in agriculture, is created. The direct and indirect effects of atmospheric (outdoor) air on humans are varied. Before considering the problem of protecting the air environment from various pollutants, let us give brief information about its structure and gas composition.

The atmosphere consists of the following main layers:

Troposphere - up to a height of 8-17 km (depending on latitude); it contains 80% of the mass of the atmosphere, concentrates water vapour and develops weather phenomena.

Stratosphere - the layer above the troposphere up to a height of about 40 km. In the upper part of the stratosphere there is a maximum concentration of ozone (O3), which absorbs most of the ultraviolet radiation of the Sun and protects the Earth's living nature from its harmful effects.

Ionosphere - a layer above the stratosphere with increased ionisation of gas molecules. This layer protects the biosphere from the harmful effects of cosmic radiation, affects the reflection and absorption of radio waves; polar lights occur in it.

Exosphere (outer sphere) - is located above the ionosphere and is otherwise called the sphere of scattering, as the gas molecules of this layer are scattered into outer space.

The exact upper boundary of the Earth's atmosphere cannot be specified, as the density of air continuously decreases with altitude, approaching the density of the substance filling the interplanetary space. Traces of the atmosphere are present at altitudes of about 10,000 kilometres or more.

The gas composition of the atmosphere near the Earth's surface is as follows: nitrogen - 78.1 per cent (by volume), oxygen - 20.1 per cent, argon - 0.9 per cent, carbon dioxide - 0.03 per cent, as well as insignificant amounts (0.01 per cent) of neon, helium, krypton, xenon, hydrogen and ozone. According to space research data, at altitudes of 250-300 kilometres the main component of the atmosphere is atomic oxygen. Even higher, starting at altitudes of 500-600 kilometres, the atmosphere becomes helium-hydrogen. And its outermost layers consist of atomic hydrogen).

In addition to gases, the atmosphere always contains a certain amount of water vapour and various impurities.

According to the World Health Organisation (WHO), air pollution causes more than 3 million premature deaths worldwide each year. Therefore, it is necessary to control the content of pollutants in the atmosphere in order to take urgent measures to reduce pollution and create a healthy environment for the population. Air pollution is determined by the input of pollutants from both natural and anthropogenic sources, as well as by the physiographic and climatic conditions of the region. A significant part of Uzbekistan represents flat territories of the Turan Lowland, which are open to cold intrusions, which forms a sharply continental climate. Periodically western and north-western intrusions of humid air from temperate latitudes of the Atlantic Ocean are observed, which also affects the qualitative and quantitative characteristics of the atmosphere. The main natural pollutants in the plains are natural sources of aerosol emissions, such as the Karakum and Kyzylkum deserts, known for their frequent dust storms, as well as the Aral Sea area, from the surface of which large masses of salt dust rise and move westwards. The main sources of anthropogenic pollutants are transport and enterprises of key industries of the Republic, including oil and gas extraction and processing, energy, metallurgy, construction, chemistry and others.

When it comes to environmental problems in Uzbekistan, it is also important to pay attention to air quality issues. Air pollution is becoming an increasingly serious problem in the country's cities due to heavy traffic, industrial activity and other sources of emissions.

The level of air pollution in some cities of Uzbekistan exceeds permissible standards, which negatively affects public health and ecosystems. Industrial emissions, road transport and activities of various enterprises are the main sources of pollution.

One of the key factors contributing to air pollution is transport, especially in large cities. The high level of emissions from motor vehicles affects air quality and the health of citizens. In 2018, 426 thousand tonnes of pollutants were emitted into the atmosphere in Tashkent. According to the Tashkent City Department of Ecology and Environmental Protection, more than 90% of this volume, which is 395 thousand tonnes, came from motor vehicles.

Atmospheric air pollution by nitrogen oxides.

Among the most significant air pollutants are nitrogen oxides, which enter the atmosphere as a result of anthropogenic emissions from industry, power plants and transport. They are formed during the combustion of organic fuels at high temperatures as nitrogen oxide (NO) and nitrogen dioxide (NO₂). In the atmosphere, nitrogen oxide (NO) is converted to nitrogen dioxide (NO₂). The average concentration of nitrogen oxides in the air of the cities of the republic ranged from 0.01 to 0.05 mg/m³. In six cities - Bekabad, Tashkent, Namangan, Fergana, Margilan and Navoi - the nitrogen dioxide content in the atmospheric air exceeded the maximum permissible concentration (MPC) by 1.3 times.

Pollution of atmospheric air by sulphur dioxide.

The main sources of sulphur dioxide in the air of cities are power plants, boiler houses and metallurgical enterprises. Sulphur dioxide enters the atmosphere during combustion of fuel containing sulphur, as well as during the processing of sulphide ores. The average concentration of sulphur dioxide in the atmospheric air of the cities in 2021 ranged from 0.001 to 0.057 mg/m3. In all cities there were no cases when the concentration exceeded the values of maximum permissible concentration (MPC), except Almalyk city, where the level of sulphur dioxide was 1.1 MPC.

Carbon monoxide (CO) pollution of atmospheric air.

Carbon monoxide enters the atmosphere from industrial plants as a result of incomplete combustion of fuel. Large amounts of carbon monoxide are emitted in emissions from metallurgical and petrochemical plants, but the main source of this gas is road transport. In 2021, the average concentration of carbon monoxide in the atmospheric air of cities ranged from 1 to 4 mg/m3. In the cities of Angren and Namangan, the level of carbon monoxide exceeded the maximum permissible concentration (MPC) by 1.3 times.

Atmospheric air pollution by solid suspended solids (dust).

Solid suspended substances include dust, ash, soot, cement, sulphates, nitrates and other particles formed during combustion of various fuels and production processes. These substances enter the atmosphere from both anthropogenic and natural sources. Anthropogenic suspended solids are industrial dust and particulate matter from the operation of various factories, as well as particulate matter emitted by motor vehicles and other sources. Naturally occurring suspended solids are generated by wind lifting soil particles into the air.

Nowadays, large-scale residential construction projects are sweeping all major cities. As a result of construction activities, the atmosphere is polluted with air containing many small and large streams of suspended matter from excavation activities. The atmosphere receives cement dust, emissions from burnt construction debris and a variety of gaseous impurities emitted by various construction aggregates. In this connection, the average concentrations of suspended substances in the atmospheric air of large cities exceed the maximum permissible values. The content of dust in the air of cities varied from 0.10 to 0.25 mg/m³. Exceeding the MPC by 1.3 times was recorded in such cities as Tashkent, Namangan, Bukhara, Samarkand and Nukus. Since March 2021, continuous observations of fine particles PM10 and PM2.5 have been started in Tashkent using automatic atmospheric air monitoring stations. These particles typically account for 40-70 % of the total suspended particles.

Table 1. Annual dust concentrations in Tashkent city in 2015-2023.

In Uzbekistan, SanPiN 0293-11 is currently in force, which contains standards only for suspended particles PM10, while standards for fine particles PM2.5 in atmospheric air have not yet been developed. As a result of the dust storm in November 2021, the average monthly maximum permissible concentration (MPC) for suspended particles PM10 was exceeded by 2.3 times. In Uzbekistan, SanPiN 0293-11 is currently in force, which contains standards only for suspended particles PM10, while standards for fine particles PM2.5 in atmospheric air have not yet been developed. As a result of the dust storm in November 2021, the average monthly maximum permissible concentration (MPC) for suspended particles PM10 was exceeded by 2.3 times.

Ozone pollution of atmospheric air.

Ozone is formed in the polluted atmosphere as a result of photochemical reactions that occur under the influence of intense solar radiation. The ozone content in the cities of the Republic varied from 0.010 to 0.083 mg/m³. Exceedances of the maximum permissible concentration (MPC) were recorded in the cities of Angren (1.2 MPC), Tashkent (1.9 MPC) and Fergana (2.8 MPC). In 2021, extremely high levels of air pollution were observed in the cities of Almalyk in January and March for sulphur dioxide - from 8.9 to 13.7 MPC, in Tashkent in July and October for dust - 9.3 and 6.0 MPC respectively, and in Chirchik in August and November for ammonia - 7.0 and 6.0 MPC respectively.

Atmospheric Air Quality Index.

The level of air pollution is determined by the Atmospheric Quality Index (AQI), which is calculated on the basis of five main pollutants: dust, carbon monoxide (carbon monoxide), nitrogen dioxide, sulphur dioxide and nitrogen oxide. If the AQI value is less than 5, it indicates a low level of pollution. The air is considered slightly polluted with an ISA of 0 to 4, moderately polluted with an AQI of 5 to 6, highly polluted with an AQI of 7 to 13, and very highly polluted with an AQI above 14.

In Uzbekistan, the Atmospheric Quality Index (AQI), which is calculated for five substances with the highest concentrations, is used for a comprehensive assessment of the atmospheric air condition. According to Uzhydromet monitoring data, in 2021 the situation with atmospheric air pollution remained stable on the territory of Uzbekistan: in the city of Andijan the AQI was 3.52, in Almalyk - 4.85, in Angren - 4.41, in Bukhara - 4.34, in Kokand - 2.83, in Margilan - 1.51, in Sariasiya - 1.38, in Tashkent - 4.67, in Navoi - 4.03, in Nukus - 3.37, in Urgench - 1.95, in Chirchik - 3.56, and in Samarkand - 3.13.

Table 2. Indicators of AQI in Tashkent city in 2015-2023.

Mainly, atmospheric pollution in the cities of the Republic of Uzbekistan is related to emissions of nitrogen, sulphur and carbon oxides, as well as dust and smoke. Apart from emissions from industrial enterprises and motor transport, there are other sources of atmospheric pollution. For example, during dust storms, which occur from autumn to spring, the concentration of dust in the atmosphere increases significantly. Also, the burning of rubbish at landfills represents an important source of air pollution, especially during the summer period.

 In general, solving the air quality problem in Uzbekistan requires coordinated efforts on the part of the state, enterprises, public organisations and citizens. Application of modern technologies, development of strict environmental standards and raising public awareness of environmentally friendly lifestyle play a key role in creating a favourable environment for life and development of the country.