How Does the Ozone Layer Change over Time?
ES1708  Dobson Units

The amount of ozone in the atmosphere is measured in Dobson Units. One hundred Dobson Units refers to the amount of atmospheric ozone that, if concentrated at the Earth's surface, would be 1 mm thick under conditions of standard temperature and pressure (0 degrees C and 14.7 pounds per square inch).

NASA
Ozone map of southern hemisphere (November 1979)

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