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Dobson Unit

The standard way to express ozone amounts in the atmosphere. One DU is 2.7 x 10 exp 16 (10 to the 16th power) ozone molecules per square centimeter. One Dobson unit refers to a layer of ozone that would be 0.001 cm thick under conditions of standard temperature (0 degree C) and pressure (the average pressure at the surface of the Earth). For example, 300 Dobson units of ozone brought down to the surface of the Earth at 0 degree C would occupy a layer only 0.3 cm thick in a column. Dobson was a researcher at Oxford University who, in the 1920s, built the first instrument (now called the Dobson meter) to measure total ozone from the ground. Source: NASA (http://earthobservatory.nasa.gov/Glossary)