Dobson
Dalton
Coulomb
None of these
The ozone layer sits in the stratosphere between 15 km and 30 km above the earth and shields us and other living things from the sun’s harmful ultraviolet radiation. Ozone layer depletion could have serious effects on human health and the environment.
Dobson Units (DU) measure how much ozone is in the air above us. On a global scale, the average total ozone concentration is typically around 300 DU. Ozone levels tend to be higher near the poles and lower at the equator. Generally, the ozone hole is defined as the area for which ozone column values amount to 220 Dobson Units (DU) or less. This is only apparent in the southern hemisphere. Here, the largest historical extent of the ozone hole — 28.4 million square kilometres — occurred in September 2000. This area is equivalent to almost seven times the territory of the EU.
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