Ground-level ozone concentrations exceeded legal limits in every EU member state, and at many individual measurement sites, in 2013, according to the European Environment Agency (EEA)'s annual report, released yesterday (13 March).

But although the number of violations of safe ozone levels was high, they have decreased in volume over recent decades, the report noted, and are at their lowest level since reporting began in 1997.

“Since 2007, ozone levels have returned to their lower and more usual levels,” the report stated. “The year 2013 was no exception.”

Recent scientific studies have shown that ground-level ozone pollution is harmful to human health even at very low levels. “This means that levels are still far too high,” the EEA says

Ozone is a harmful pollutant that has been shown to harm lung functioning, irritate respiratory systems and increase the risk of death from cardiovascular and respiratory failure.  

The EU’s long term objective of containing ozone concentrations was exceeded in 83% of reporting stations, and at least once in every EU member state, according to the EEA.   

The ‘alert threshold’ at which ozone concentrations are twice the level considered harmful to human health was broken 27 times.

This mostly happened during July and the first days of August in 2013, with Mediterranean and Alpine regions being the worst affected.

In some countries, up to two-fifths of the population were exposed to levels exceeding limits, the report says.

A separate study found that in 2012, almost all inhabitants of cities in the EU were exposed to ozone levels above World Health Organisation guidelines, which are stricter than the EU limits.

Ground-level ozone is a 'secondary pollutant', which means it is formed in chemical reactions between other pollutants in the air, particularly in warm weather.  

In December 2013, the European Commission adopted a Clean Air Policy package to reduce emissions, including those of ozone percursors, introducing new objectives for 2030.