In the air there are regular parts and impurities, the content of which depends on many reasons. To constant parts include air gases: oxygen, nitrogen, carbon dioxide, argon, neon, helium, methane, krypton, nitrous oxide, hydrogen, xenon headlights, ozone and radon.
Oxygen (see) is a key component of air. In nature, always carried the processes of consumption and recovery of oxygen, so the content in the atmospheric air almost constantly (20,95%). Nitrogen (see) is the volume of the main part of the air (78,09%). He plays the role of inert diluent oxygen (oxygen life is impossible). Carbon dioxide (see) is present in ambient air in a small amount (0,03%): atmospheric air is constantly updated with carbon dioxide as a result of life processes of living organisms, burning, fermentation and other, however, parallel to this is the absorption of carbon dioxide by plants, for which he is the source of carbon in the synthesis of organic substances. The increase in the concentration of carbon dioxide is observed in air of cities, which is explained by entering it with the emissions of industrial enterprises, boiler houses and other carbon dioxide Content in the air of residential premises is an indicator of air pollution and shall not exceed 0.1%. Inert gases (argon, neon, and others) in those very small quantities in which they are usually present in the air, do not participate in any reactions and do not affect humans.
To constant integral part of atmospheric air are also water vapour and dust. Water vapour comes into the air through evaporation of water vast water surface. Their content varies widely depending on various physical processes, continuously takes place in the atmospheric air. The content of water vapor in the air characterizes its humidity. The source of the dust contained in the air, is the Earth's surface; a mixture of cosmic dust in the atmospheric air is insignificant. The dust content of the air increases in the cities as a result of arrival of dust emissions of industrial enterprises, boiler houses, etc., (see Dust).
Besides regular parts, in the air usually contains various gases coming, like dust, emissions from industrial enterprises, power plants, with exhaust gases of motor transport. The most frequent gas air impurities are: sulfur dioxide, carbon oxide, hydrogen sulphide, chlorine, various nitrogen compounds, aromatic substances, etc. the Content of these substances in the atmospheric air can reach such quantities that have adverse effects on living conditions and health of the population. Therefore, in the USSR developed and implemented national measures to reduce air pollution and the law on sanitary protection of atmospheric air (see Sanitary protection of atmospheric air) .
Air also contains various microorganisms (bacteria, spores, mold fungi), which in majority are saprophytes, i.e. do not cause disease in humans and animals. Pathogens found in open atmosphere in small quantities, but to air their content above. Source of pathogenic organisms in this case are the people (usually bakterionositeli)that produce them and saliva, mucus when talking, coughing and sneezing.
Great value for a person have physical properties of air temperature, humidity, fluidity. For a man, dressed easily and at rest, the most favorable is the temperature 18-20. The heavier executed by the person, the work, the lower temperatures are required to save thermal equilibrium.
Great hygienic importance and humidity, which affect teploregulyation of the body. High humidity at low temperatures of air entails the loss of body heat (due to the large thermal conductivity humid air, and at high temperatures - overheating (impeded by the evaporation of sweat). Humidity of 40 to 60% of the most meets the requirements of thermal comfort for the person. People very sensitive to air movement: high speed of air movement (5-10 m/s) may have adverse effect on respiration and cardiovascular system; medium and low - change the heat of the body and thereby affect the thermal balance of the person.
Permissible air velocity in premises not more than 0,3-0,5 m/sec. Considering the impact on humans of temperature, humidity and air movement, it is necessary to consider their combined effect.
In the USSR developed a special standards of composition and physical properties of the air, and measures to maintain the purity of the air and favorable climate (see) in different rooms (standards of temperature, relative humidity and speed of movement of air in the facilities - see table pdf (KB). This develops a rational system of ventilation, heating, conditioning and air purification. Very important are also the ventilation, regular cleaning and so on (see Housing).