Influence of ozone depletion on UV exposure

Source: @nt/Stock.adobe.com

The ozone in the atmosphere ensures that not all of the UV radiation emitted by the sun (solar UV radiation) reaches earth. This filtering effect of ozone is highly wavelength-dependent: the shorter the wavelength of the UV radiation, the less of it reaches earth. Accordingly, longwave UVA radiation with wavelengths of 315 nm to 400 nm passes through the ozone layer unimpeded, while just 10% of UVB radiation (wavelengths of 280 nm to 315 nm) reaches earth. UVC radiation (280 nm to 100 nm) doesn’t reach earth at all.

Changes in the atmospheric ozone level lead to changes in the proportion of UVB radiation that reaches earth: a lower ozone concentration means an increase in the proportion of UVB, whereas a higher ozone concentration reduces the proportion of UVB.

An increase in the proportion of UVB leads to an increase in the general public’s total exposure to UV radiation. This results in an increased risk of UV-related diseases and especially of UV-related cancers of the skin and eye.

Fluctuations in ozone level

Some 90% of all ozone in the atmosphere is found in the stratosphere, while some 10% is found in the underlying troposphere. At our latitudes, the total atmospheric ozone level undergoes natural seasonal fluctuations, reaching a maximum in spring and a minimum in autumn.

Low-ozone events can also occur for a variety of reasons: on the one hand, pronounced ozone depletion can occur over the Arctic during very cold winters, and the resulting low-ozone air masses can be transported to temperate latitudes when the polar vortex breaks down. This can then lead to a few days of unusually high UV intensities in late March/early April in Germany, which can temporarily increase the UV index by up to three UV index values. On the other hand, there can also be an influx of low-ozone air from subtropical latitudes, leading to UV intensities above the usually expected level for a few days in Germany.

The Federal Office for Radiation Protection monitors this closely and issues timely warnings via the BfS’s UV-Newsletter and Twitter.

Anthropogenic ozone depletion

Anthropogenic ozone depletion is not only the cause of the hole in the ozone layer over the Antarctic but has also led to a more or less pronounced increase in the proportion of UVB at the global level. At mid-latitudes in the northern hemisphere – and therefore also for Germany – there has been an approximately 3% depletion of the stratospheric ozone layer. This has led to an increase in sunburn-causing UV irradiance by approx. 7% in winter/spring and by approx. 4% in summer/autumn.

The earth’s ozone layer now appears to have recovered thanks to adherence to the Montreal Protocol. It is anticipated that the ozone layer thickness over mid-latitudes of the northern hemisphere will return to the levels of the 1980s in the 2030s. However, there are also indications that interactions between greenhouse gases (keyword: global warming, climate change) and ozone-forming processes in the atmosphere may slow down this recovery.