he map above shows the size and shape of the ozone hole over the South Pole on the day of its 2024 maximum extent. Moderate ozone losses (orange) are visible amid areas of more potent ozone losses (red). Scientists describe the ozone “hole” as the area in which ozone concentrations drop below the historical threshold of 220 Dobson units.

What Is a Dobson Unit?

The Dobson Unit (DU) is the standard measurement for ozone concentration in Earth’s atmosphere. It quantifies the total amount of ozone in a column of air from the surface to the edge of space. One Dobson Unit equals a 0.01-millimeter layer of pure ozone at standard temperature and pressure. For example, 300 DU would form a 3-millimeter ozone layer if compressed. Scientists use Dobson Units to observe ozone health globally, providing insight into seasonal thinning and recovery patterns.