Dobson unit
From Glossary of Meteorology
A unit used in the measure of the column abundance of ozone in the atmosphere.
One Dobson unit is the equivalent of 2.69 × 1016 molecules of ozone per square centimeter. Alternatively, 1 Dobson unit corresponds to a layer of ozone 10 μm thick, if the ozone were held at standard temperature and pressure (273 K, 1 atm pressure).