Figure 2 b shows the differences in total ozone between the two simulations on 25 March.

The ozone hole is defined as the size of the region with total ozone below 220 Dobson units.

In the 1920s, he built the first instrument to measure total ozone from the ground, now called the Dobson ozone spectrophotometer.

The size of the Arctic area of anomalously low total ozone in 2004-2005 was larger than in any year since 1997.

The Dobson Ozone Spectrophotometer has been used to study total ozone since its development in the 1920's.

Maintain and improve the current total ozone and ozone profiling network.

Dobson units are a measure of total ozone in a vertical column of air.

The result is a high quality data set usable to derive trends with respect to total ozone.

From this information, the total ozone between the instrument and the ground can be calculated.

Is total ozone uniform over the globe?