Dobson unit

Dobson units (DU) are the standard way to express ozone amounts in the atmosphere. One DU is 2.7 x 10¹⁶ (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 °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.