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Ozone, UV and a hole in the ozone layer

Ozone is a gas that is naturally present in the Earth’s atmosphere. The ozone is distributed upwards into the atmosphere; about 10% is in the layer closest to the Earth (the troposphere, from the surface to about 15 km altitude), and the remaining 90% is in the stratosphere (15-50 km). Together, they form the ozone layer, which covers the entire globe in varying thicknesses.


The ozone layer protects the Earth against harmful ultraviolet (UV) radiation by absorbing sunlight with wavelengths between 290 and 320 nanometres. Solar radiation with a wavelength up to 320 nanometres is called UV-B, and it is this radiation that causes sunburn.

If the ozone layer gets thinner, larger doses of harmful ultraviolet radiation (UV-B) reach the Earth’s surface. When there are ozone holes over Antarctica, UV radiation there can be more intense than in sunny San Diego, California. Too much UV radiation can not only cause sunburn, but can also weaken our immune system and increase the risk of skin cancer and infectious diseases. High UV radiation can also damage plants and animals, and lead to reduced yields and failures in food production. The ocean’s ecosystems could also be damaged.

Holes in the ozone layer

The phenomenon called an “ozone hole” is a sharp reduction in ozone that takes place over the South Pole every year in September-November. This annual phenomenon started in the 1980s, and it lasts for about 2-3 months.

Anthropogenic emissions of chlorine-containing substances (CFCs) are an important cause of ozone depletion over Antarctica. The reason we seldom have similar ozone holes across the North Pole is two-fold: the stratosphere is usually warmer over the Arctic than the Antarctic. Thus, CFCs do not have the same ozone-depleting effect in the north. In addition, the Antarctic has a persistent, powerful cyclone in the middle and upper troposphere and the stratosphere – this cyclone prevents inflow of ozone-rich air from lower latitudes into the Antarctic. The corresponding vortex over the Arctic is less stable, which means that the ozone holes in the north are rarely as powerful and long-lasting as those in the south.

Thanks to international agreements (of which the Montreal Protocol is most important), the production and emissions of ozone-depleting gases have been greatly reduced. In 2014, the United Nations Environment Programme (UNEP) and the United Nations World Meteorological Organization (WMO) published a report showing that if recent years’ positive trend continues, the ozone layer will be back at the 1980 level around 2050.

Ozone monitoring at NILU

NILU monitors changes in the atmospheric ozone layer from Blindern in Oslo, and at Andøya, outside of Tromsø. Ozone is also measured in Ny-Ålesund, at the Sverdrup station.