Ozone through time
Today, average rural ozone concentrations in Europe are three times higher than in the pre-industrial era. This is most likely a result of increases in emissions of the ozone precursors NOx and VOC since the beginning of the 20th century.
Since 1990, however, emissions of ozone precursors in the EU have declined by about 30 %. This has been due mainly to the widespread introduction of catalytic converters in cars and new EU laws to reduce air pollution.
This has not, however, resulted in comparable declines in average ozone concentrations, especially in city centres. This may be explained by the fact that formation of ozone depends on complex chemical processes, as well as on sunlight and climatic conditions.
More information on long-term air pollution trends can be found in the EEA's core set of indicators.