Ozone smog surges over summer

Ground level ozone frequently breached critical limits during summer, according to a new report showing that levels of ozone exceeded warning thresholds somewhere in Europe on more than three days out of four.

According to EU law, governments must inform the public whenever monitoring stations detect ozone above a critical threshold, set at 180 micrograms of ozone per cubic metre of air averaged over one hour.

The European Environment Agency found that over the April-August 2002 period, this threshold was exceeded in 11 of the 15 EU Member States. Excess ozone occurred in at least one country on 120 of the 153 days covered. June and July saw the highest number of breaches.

The EEA report found that the warning threshold was breached in France, Greece, Italy and Spain over all five months monitored. Total excesses were highest in southern France and central Italy. Austria, Germany and Switzerland saw thresholds breached over four consecutive months while the Netherlands and the Czech Republic recorded high ozone in three consecutive months. Greece reported the highest number of days with excess ozone – 68 – followed by France (56), Italy (52) and Spain (48).

The countries that recorded no threshold breaches included Denmark, Estonia, Finland, Ireland, Norway and Sweden. For Ireland and Finland, 2002 marks the sixth consecutive year without above-threshold ozone.

A new EU directive in force in September 2003 sets a new “alert” threshold. When exceeded, governments will have to act to produce an immediate reduction of ozone pollution, where feasible. The average of the maximum ozone concentration recorded this year is slightly higher than in 2001 but the average duration of breaches is lower. Year-to-year variations are due to changes in summer weather and the extent of the monitoring network.

Ozone, the main component of summer smog, forms when air pollutants emitted by industry and transport react with sunlight. Ozone levels tend to be highest during warm, sunny weather, and are generally higher in southern Europe than in the north.

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