structural:reformatting, structural:expansion, quality:correction
Ozone in Earth's atmosphere

The standard way to express total ozone levels (the amount of ozone in a given vertical column) in the atmosphere is by using Dobson units. Point measurements are reported as mole fractions in nmol/mol (parts per billion, ppb) or as concentrations in μg/m. The study of ozone concentration in the atmosphere started in the 1920s.