1. Ozone

1.1 Physico-chemical properties

Ozone is composed of three oxygen atoms. It is naturally present in the atmosphere in very low concentrations. In the stratosphere, it acts as a protective filter, absorbing harmful UVC radiation. At ordinary temperatures, ozone is an unstable gas, blue in color when observed in sufficient thickness, with a characteristic odor detectable at levels of 0.01 to 0.05 ppm, which gives it its name (from the Greek ozein, to exhale an odor). The main physical and thermodynamic constants of ozone are listed in table 1