We limit our discussion to the 'troposphere', meaning the closest layer of the atmosphere to the earth with a thickness of about 15 km.
Geography of course gives you more information.

The composition of air
The normal composition of dry and clean air in percentages (so without counting with humidity and pollution):

Nitrogen 78
Oxygen 21
Argon 1
Carbon dioxyde 0,04 (!)
other noble gases 0,003

You know that the air may contain a certain percentage of water vapor (humidity).
The humidity can vary from extremely dry (0%) to very humid (100%)

The components of air - in general - are non polar substances.

It is possible to separate the air components in a process of fractionated distillation.
But that is only possible with liquid air, and you must do that at very low temperatures.

Ozon and Carbon dioxyde belong in the atmosphere. Carbon dioxyde is not poisonous, but may not increase to much (what unfortunatele happes the last hundred years). It is risky.
Ozon is located very high in the atmosphere (fortunately, because ozon is poisonous for living creatures). The Ozon above has an important function: it absorbs (holds) the ultra violet radiation from the sun.

Substances that do not belong to normal air, mostly are air polluters like (fine) dust, Carbon monoxyde, Sulphur dioxyde, the various Nitrogen oxydes, mostly coming from combustion processes.

The last hundred year the amount of CO2 in the air has increased to 0.04%. It never was that high since humans are on earth.
If CO2-production continues, lot of sun heat will be absorbed on earth in stead of being reflected to space.
The earth can get hotter, the oceans fuller, climate changes.