The part of the atmosphere that adjoins the Earth and which a person breathes accordingly is called the troposphere. The troposphere has a height of nine to eleven kilometers and is a mechanical mixture of various gases.
The composition of the air is not constant. Depending on the geographical location, terrain, weather conditions, population density, air can have a different composition and different properties. Air can be gassed or discharged, fresh or heavy - all this means that it has certain impurities.
However, the following composition of air in percent is considered standard:
- nitrogen - 78.9 percent;
- oxygen - 20.95 percent;
- carbon dioxide - 0.3 percent.
In addition, other gases are present in the atmosphere (helium, argon, neon, xenon, krypton, hydrogen, radon, ozone), as well as nitrous oxide and water vapor. Their amount is slightly less than one percent.
It is also worth noting the presence in the air of some constant impurities of natural origin, in particular, some gaseous products that are formed as a result of both biological and chemical processes. Among them, ammonia deserves special mention (the composition of air away from populated areas includes about three to five thousandths of a milligram per cubic meter), methane (its level is on average two ten thousandths of a milligram per cubic meter), nitrogen oxides (in the atmosphere their concentration reaches approximately fifteen ten thousandths of a milligram per cubic meter), hydrogen sulfide and other gaseous products.
In addition to vaporous and gaseous impurities, the chemical composition of air usually includes dust of cosmic origin, which falls on the surface of the Earth in the amount of seven hundred thousand tons per square kilometer during the year, as well as dust particles that come from volcanic eruptions.
However, the composition of the air and (to the worse) changes to the greatest extent and pollutes the troposphere by the so-called ground (plant, soil) dust and smoke from forest fires. Especially a lot of such dust in the continental air masses originating in the deserts of Central Asia and Africa. That is why it can be stated with confidence that a perfectly clean air environment simply does not exist, and it is a concept that exists only theoretically.
The composition of the air tends to constantly change, and its natural changes usually play a rather small role, especially in comparison with the possible consequences of its artificial disturbances. Such violations are mainly associated with the production activities of mankind, the use of devices for consumer services, as well as vehicles. These violations can lead, among other things, to air denaturation, that is, to pronounced differences in its composition and properties from the corresponding atmospheric indicators.
These and many other types of human activity led to the fact that the basic composition of the air began to undergo slow and insignificant, but nonetheless absolutely irreversible changes. For example, scientists estimate that over the past fifty years, humanity has used about the same amount of oxygen as it did in the previous million years, and as a percentage, two tenths of a percent of its total supply in the atmosphere. At the same time, the emission of carbon dioxide into the air envelope of the Earth increases accordingly . This release, according to recent data, has reached almost four hundred billion tons over the past hundred years.
Thus, the composition of the air is changing for the worse, and it is difficult to imagine what it will become in a few decades.