ozone

A trace gas present in the atmosphere, whose highest concentrations are reached between 20 and 25 kilometers of altitude (stratospheric ozone) and also in urban and industrial areas (tropospheric ozone). Colloquially, one speaks of "good" and "bad" ozone, respectively, due to the - beneficial or harmful - role it plays. The ozone molecule is the triatomic form of oxygen. It is the result of the union of an oxygen molecule with a free atom of the same element. Its chemical formula is O₃ and among its characteristics its blue color and an intense metallic smell stand out, which is perceived very clearly when there is a storm with strong lightning activity. Lightning strokes, on their path through the air, dissociate oxygen molecules, leaving free atoms of that element which, on joining with other undissociated molecules, form ozone. That property is the reason behind its name, as it has its origin in the Greek term ὂζειν (ozein ), meaning to smell. In the troposphere, apart from forming spontaneously, it is a secondary pollutant generated by photochemical reactions in which NOx and VOCs (volatile organic compounds) combine with oxygen. At high concentrations, it is harmful to health, being a powerful oxidant and also acting as a greenhouse gas. Stratospheric ozone, located mainly in the ozonosphere, plays an important role in the radiative balance of the stratosphere, due to its great capacity to absorb ultraviolet radiation coming from the sun. It forms a kind of shield preventing the most energetic and lethal fraction of that radiation (types B and C) from reaching the Earth's surface, which makes life on Earth possible.