Unlike stratospheric ozone that protects life on earth, tropospheric ozone is highly toxic and is the main pollutant of the atmosphere of industrialized countries and cities. Its precursors are emanated from industrial activities and traffic. Generated by lightning, photochemical reactions or with free radicals, it has a density of times greater than air and is maintained close to the ground. It decomposes easily, generating free radicals with oxidizing power. The main primary pollutants leading to ozone formation are nitrogen oxides, volatile organic compounds and methane. The amount of tropospheric ozone varies in different areas and in time, its assessment is very difficult, monitoring of the precursor being necessary. Atmospheric pollution, by blocking some.
