Measuring Stratospheric Ozone


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 Satellites looking down on the Earth from space can measure the amount of ozone in the atmosphere, as shown in the image to the left. The unit used to measure the amount of ozone is called the Dobson Unit .

The image to the left is the average amount of ozone over the North Pole for the month of March (Spring) 1980.

The levels are colour-coded for easy analysis. The large white "dot" in the centre (at the North Pole position) is not an ozone hole...it appears white because there is no data for the region.

The ozone concentration ranges from 500 Dobson Units over Siberia to a low of about 350 Dobson Units over Scandinavia. (The low perimeter values should be ignored.)


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What's a Dobson Unit?

One Dobson Unit (1Du) is equivalent to a layer of pure ozone 0.01mm thick at sea-level pressure.

For example, if the ozone concentration in the atmosphere above you is 425 Du's, then that would be identical to having a thin layer of pure ozone 4.25mm thick over your head (at sea-level pressure).

The sketches to the left show (approximately) the ozone thickness appropriate to each ozone concentration. In the Earth's atmosphere the ozone is actually spread out over a layer 20-50 km in thickness so that its density is really extraordinarily small.


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 The graph to the left allows a quick conversion from Dobson Units to sea-level pure-ozone equivalent thicknesses.

An even simpler method is to multiply the Dobson unit concentration by 0.01mm.

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