Unit used in geophysics to measure the ozone in the atmosphere.
One Dobson unit represents the amount of atmospheric ozone that would form a uniform layer 0.01 millimetre thick at standard temperature (0°C) and pressure (1013.25 millibars).
Under normal conditions the atmosphere contains around 300 Dobson units of ozone. This drops to 100 Dobson units where there are Ozone Holes.
See also: Ozone.