International Day for Preservation of the Ozone Layer, 16 September

Depletion of the ozone layer

Published:

Emissions of gases containing chlorine and bromine, such as CFCs, HCFCs and halons, deplete the atmospheric ozone layer. The ozone layer protects the Earth against harmful UV radiation from the sun. Excessive UV radiation may cause damage to people, plants, animals and marine ecosystems. Scientists estimate that if all countries comply with the requirements of the Montreal Protocol, the ozone layer will recover by 2050.

Written by: Frode Brunvoll / Gisle Haakonsen



The stratospheric ozone layer

The ozone layer is found in the stratosphere, between 15 and 35 km above the Earth's surface. Ninety per cent of the ozone (O 3 ) present in the atmosphere is concentrated here. Ozone is continually generated and broken down through natural processes in the stratosphere.

 


Facts about the ozone layer and UV radiation

  • The ozone layer varies in size with the seasons. At our latitudes it is thickest in March-April and thinnest late in the autumn. Because the greatest seasonal variations occur at the poles, there are only slight or no seasonal variations around the equator.

  • The ozone layer is thinnest near the equator and the thickness increases with increasing latitude. In the Northern hemisphere the ozone level is highest at 60º to 70º N.

  • If the ozone in the atmosphere were to be compressed to ground level pressure, it would form a layer approximately 2-5 mm thick.

  • The annual effective UV dose increases with a factor of about 4 from Oslo to the equator. This corresponds to a 7 per cent increase per latitude.

  •  

    Source: Henriksen, T., Henriksen, E. K. and Svendby, T. (1994): ” Deilig er den himmel blå ”. Ozonlag . UV-stråling . Drivhuseffekt . Theme report on environmental physics. University of Oslo. August 1994 (in Norwegian only).

Increased radiation may have dramatic effects

Towards the end of the Permian period - 250 million years ago - many species became extinct and 90 per cent of marine life was killed off. Recent investigations indicate that the reason for this ecological crisis was massive volcanic activity that released large amounts of ozone-damaging particles into the atmosphere, causing increased UV radiation. The high radiation intensity damaged plant DNA and caused mutations and severe effects on the reproductive capacity of plants, which in turn caused an ecological collapse.

The ozone hole

The largest decreases in ozone concentrations have been observed over Antarctica, particularly in the months of September and October. In this so-called ozone hole, up to 60 per cent of the total ozone is lost. After a couple of months new ozone is produced and the ozone layer regenerates until the next cycle starts. This phenomenon was first observed in the early 1980s (Norwegian Pollution Control Authority 2004).

Five per cent of the ozone layer lost since 1969

Measurements have shown a decline in global stratospheric ozone levels over the last 20 years. Since 1969, the global average loss of ozone has been 5 per cent at middle latitudes. Ozone-depletion of up to 10 per cent during the winter and spring and up to 5 per cent during the summer and autumn has been recorded over Europe, North America and Australia. If we ignore the effect of other factors that have an impact on the ozone layer, such as climate changes and volcanic activity, it seems probable that the ozone layer is now at its thinnest.

On behalf of the Norwegian Pollution Control Authority, the Norwegian Institute for Air Research (NILU) monitors the ozone levels over Oslo, Tromsø, and the Svalbard archipelago. In the period 1979-2003 an annual reduction of the ozone layer of 0.21 per cent was recorded over Oslo.

 


The Montreal Protocol

In 1987, the Montreal Protocol was adopted with the aim of reducing global production and consumption of ozone-depleting substances. If all countries comply with the requirements of the protocol, the ozone layer is expected to recover by 2050.

National targets - climate change, air pollution and noise

Depletion of the ozone layer

1. The consumption of halons, all types of chlorofluorocarbons (CFCs), tetrachloromethane, methyl chloroform and hydrobromofluorocarbons (HBFCs) shall be eliminated.

2. Consumption of methyl bromide shall be stabilised in 1995 and phased out by 2005.

3. Consumption of hydrochlorofluorocarbons (HCFCs) shall be stabilised in 1995 and phased out by 2015.
Imports of ozone-depleting substances
  • Imports of ozone-depleting substances to Norway have been very low in recent years. However, because these substances have a long lifetime emissions are still generated by the use and replacement of old products that contain ozone-depleting substances, although such emissions are dropping as old products are being phased out.
  • Norway has fulfilled its commitments under the Montreal Protocol and the EU targets for ozone-depleting substances. Measured in ODP-tonnes, the countrys consumption of ozone-depleting substances has been reduced by 99 per cent since 1986.


Links

Norwegian Pollution Control Authority: State of the Environment Norway

Norwegian Institute for Air Research: Ozone and UV

Statistics Norway: Natural Resources and the Environment. Norway

Contact