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Summer ozone: record low concentrations in 2009

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Ozone levels in Europe during summer 2009 were among the lowest since comprehensive data reporting started in 1997.

Eighteen EU Member States reported exceeding the information threshold (ozone concentrations over 180 µg/m3), with Belgium, Greece, Italy and Portugal recording the largest number of exceedances. As in most previous years, no station in northern Europe registered information threshold exceedances.

Eight EU Member States (Bulgaria, France, Greece, Italy, Portugal, Romania, Spain and the United Kingdom) reported exceeding the alert threshold (ozone concentrations of 240 µg/m3).

The record lows in 2009 came despite average summer temperatures close to those measured in the extremely hot summer of 2003, which witnessed the highest number of exceedances in the last decade. The differing results in the two summers may be attributable to several factors because ozone formation is determined by various meteorological conditions, as well as the chemical composition of the atmosphere. It seems likely, however, that reductions in anthropogenic ozone precursor gas emissions in Europe contributed significantly to the general decrease in peak ozone concentrations.

For the first time since 1997, no concentration higher than 300 µg/m3 was reported. The highest one-hour ozone concentration (284 µg/m3) was observed in France.

In contrast to previous summers, in 2009 there were no widespread multi-day episodes. Summer 2009 was characterised by ozone episodes of between two and five days followed by spells with few exceedances.

Whereas ozone forms a protective layer in the stratosphere, at ground level it is a harmful air pollutant that affects human health. Sources of ozone precursor emissions include power plants, cars and trucks, and certain paints and solvents. In the summer, ozone concentrations are worsened by relatively light winds and higher temperatures.

EU Directive 2002/3/EC sets the long-term objectives for reducing ground-level ozone pollution to protect human health and the environment: an alert threshold (240 µg/m3) and an information threshold (180 µg/m3). Member States must report exceedances of both thresholds to the European Commission and the European Environment Agency.

As in all previous years, the Directive's long-term objective to protect human health (maximum ozone concentration of 120 µg/m3 over 8-hours) was exceeded in all EU Member States and other European countries.

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