Dobson unit (DU)

Definition

Unit of ozone in atmosphere. One DU refers to a layer of ozone that would be 0.001 cm thick under conditions of standard temperature (0 °C) and pressure (one atmosphere or 1013.25 millibars). It translates into approximately 2.7 x 1016 ozone molecules per square centimeter. Under normal conditions, earth's atmosphere contains about 300 DU of ozone, but in 'ozone holes' over polar caps it falls to 100 DU or less. Named after the UK geophysicist Dr. G. M. B. Dobson (1889-1976) who in 1928 invented the photoelectric spectrophotometer (also called Dobson meter) used in measuring the total ozone over an area from the ground.