What is a Dobson Unit?

A Dobson Unit (DU) is a unit of measurement specifically used to measure the amount of ozone in the Earth’s atmosphere. It essentially represents the thickness of a layer of pure ozone that would be created if all the ozone molecules in a vertical atmospheric column were compressed to standard temperature and pressure (STP) conditions.

One Dobson Unit is equal to a layer of ozone 0.01 millimetres thick at a temperature of 0 degrees Celsius and a pressure of 1 atmosphere. So, a reading of 300 Dobson Units (DU) of ozone signifies that the ozone molecules in that atmospheric column would create a pure ozone layer 3 millimetres thick at STP.

It’s important to remember that ozone is not uniformly spread throughout the atmosphere. The Dobson Unit provides a convenient way to express the total amount of ozone in an atmospheric column, even though the ozone isn’t concentrated in a single layer.

Dobson Units are named after G. M. B. Dobson, a scientist who developed the first spectrometer specifically designed to measure ozone from the ground. This instrument, the Dobson ozone spectrophotometer, is still used worldwide today.