Damage to vegetation

Among the air pollutants that cause direct damage to plants, ground-level ozone is by far the most significant. The ozone is formed from nitrogen oxides and volatile organic compounds in the air, under the influence of sunlight.

In plants, it has been found that damage can occur at concentrations only slightly higher than current background levels. This has a significance on yields from agriculture and forestry, as well as affecting natural ecosystems.

Measurements that have been in progress since the 1950s show that the levels of ozone in the air over Europe have risen by an average of two per cent a year, and that the background level today is two to four times as high as it was in the 1950s. The critical levels, which were presumably only exceeded occasionally at the start of the last century, are now exceeded regularly over almost all of Europe.

The limits that have been set to protect people's health are also regularly exceeded by a significant degree. The situation is worst in the Mediterranean countries of Italy, France, Greece and Spain, and in parts of Germany.

The ozone layer in the stratosphere, at an altitude of 10-40 kilometres, protects us from ultraviolet radiation from the sun and is an essential requirement for all higher life on the Earth. But when ozone is present at ground level it may be harmful to people, animals, plants and materials.