The ozone (O3) is a substance whose molecule is composed of three oxygen atoms, created at the dissociation of the two atoms that compose the oxygen gas. Each released oxygen atom connects to another gaseous oxygen molecule (O2), forming ozone molecules (O3).
At the ambient temperature and pressure it is a pungent-smelling, generally colourless gas, but at great concentrations it can easily turn bluish. If inhaled in large quantities it can cause eye or throat irritation, which usually goes away after inhaling fresh air for a few minutes.
The ozone is the first allotrope of a chemical element that science identified. Nowadays it is not very sure who initially discovered it, as there are more possible candidates. Various studies state that chemists Charles Fabry and Henri Buisson were the ones who discovered the ozone layer in 1913.
In 1785 the Dutch chemist Martinus vam Marum noticed a strange smell while he was conducting experiments with electric sparks across water that he attributed to electrical reactions without realizing that in fact he had created ozone. Half a century later, Christian Friedrich Schönbein sensed the same pungent odour and recognized it as the smell that was often perceived in thunderstorms after a lightning strike.