Air pollution by ozone

Ozone is a 'secondary' pollutant formed from gases such as nitrogen oxides and volatile organic compounds in the presence of solar light. Ozone levels typically become particularly high in regions where considerable emissions of these gases combine with stagnant meteorological conditions, high levels of solar radiation and high temperatures during the summer. Summer refers to the period from April to September.

Exposure to high ozone concentrations can cause breathing problems, trigger asthma, reduce lung function and cause lung diseases.

Ozone is regulated under the Air Quality Directive 2008/50/EU, which set some thresholds for ozone concentrations:

  • Information threshold: 1-hour average ozone concentration of 180 μg/m3, 
  • Alert threshold: 1-hour average ozone concentration of 240 μg/m3, 
  • Long term objective (LTO): the maximum daily 8-hour mean concentration of ozone should not exceed 120 μg/m3, 
  • Target value (TV): LTO should not be exceeded on more than 25 days per calendar year, averaged over 3 years. 

For description purposes a target value threshold (TVt) is also considered: LTO should not be exceeded on more than 25 days in a calendar year (instead of over the 3 year average).

Until 2014, Member States had to officially report on the summer ozone exceedances of these thresholds. Based on this past reporting, the European Environment Agency has published annual Technical Reports analysing the summer ozone situation across Europe. After the entry into force of new EU rules for reporting air quality information (Commission Implementing Decision 2011/850/EU) a new system for reporting data was established.

Summer 2014 ozone assessment

Summer 2014 ozone assessment

Overview of exceedances of EC ozone thresholds values for April-September 2014

Summer 2014 ozone assessment - Read More…

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European Environment Agency (EEA)
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1050 Copenhagen K
Phone: +45 3336 7100