Q.The 'thickness' of Stratospheric Ozone layer is measured in/on:

Stratospheric ozone — "good" ozone, distinct from the harmful "bad" ozone found near ground level — forms a protective layer in the upper atmosphere that absorbs dangerous ultraviolet (UV) radiation from the Sun before it can reach the surface, since UV radiation readily damages the DNA and proteins of living organisms. The total ozone in a vertical air column is measured in Dobson units.

Ozone is continuously formed and broken down in the stratosphere, normally in a stable balance; this balance is disrupted by chlorofluorocarbons (CFCs), widely used as refrigerants, which drift up into the stratosphere where UV radiation splits them apart, releasing chlorine atoms that catalytically destroy ozone without themselves being consumed — so a single chlorine atom can degrade many ozone molecules, giving CFCs long-lasting effects on ozone levels. Depletion is most severe over Antarc …