Depending on locality, climate and season, atmospheric air contains inclusions to a larger or lesser extent. The most important gaseous inclusions are: Ozone O3, is formed from the oxygen of the air under the effect of electrical discharge or during evaporation. Ozone has a peculiar smell and is poisonous in high concentrations. Inclusion in air is about 0.02 - 0.1 mg/m3. Carbon monoxide CO, very poisonous, odourless gas, decomposes the red blood corpuscles and is generated by incomplete combustion, thus being contained in fuel gases as well as in tobacco smoke. Urban and industrial areas suffer CO pollution at an average of about 40 - 500 mg/m3. Sulphur dioxide SO2 is created by the combustion of coal and fuel oil and has a negative effect on all forms of life if present in larger concentrations. Percentage in air is about 0.1 - 5 mg/m3.
Ammonia NH3, a pungently smelling gas from coal combustion and putrefaction. In free air, ammonia is contained to an extent of about 0.02 - 0.05 mg/m3. Apart from heating and bituminous gases, residential areas contain few inclusions in air, contrary to industrial areas where considerable concentrations of gaseous impurities are contained in the air.
