Dobson units (DU) are the standard way to express ozone amounts in the atmosphere. One DU is 2.7 × 1016 ozone molecules per square centimetre, or 2.7 × 1020/m˛. One Dobson unit refers to a layer of ozone that would be 10 micrometre thick under standard temperature and pressure. For example, 300 Dobson units of ozone brought down to the surface of the Earth at 0 degrees celsius would occupy a layer only 3 mm thick.
Gordon Dobson was a researcher at the University of Oxford, who, in the 1920s, built the first instrument (now called the Dobson meter ) to measure total ozone from the ground.