Ozone layer thickness is measured in :

The correct answer is (B) Dobson units.

• Ozone layer thickness is measured in Dobson units (DU). One Dobson unit is defined as the number of molecules of ozone that would be required to create a layer of pure ozone 0.01 millimeters thick at a temperature of 0 degrees Celsius and a pressure of 1 atmosphere.
• The Dobson unit is named after G.M.B. Dobson, a British physicist and meteorologist who pioneered the measurement of atmospheric ozone from the ground in the 1920s. A reading of 300 DU is typical for the global average ozone layer.
• Option (A) Decibels measures sound intensity, Option (C) PPB stands for parts per billion, and Option (D) PPM stands for parts per million; both PPB and PPM are standard units of concentration for trace gases in the atmosphere, but not for total column ozone thickness.