The exceptionally warm weather and long hours of sunshine in recent weeks have increased ozone pollution to dangerous levels, especially around Europe's cities with their high concentration of cars.

France's ozone levels for August are the highest since records began in 1991. In Paris, where ozone concentration topped 200 microgrammes per cubic metre -- 65 percent above the 120 microgrammes considered "safe" for humans, speed limits were still in force Wednesday.

Although ozone high in the earth's atmosphere is a vital shield against the sun's ultraviolet radiation, the gas can be harmful to human health when it builds up at ground level.

High concentrations are formed from reactions between nitrogen dioxide and hydrocarbon emissions from cars, especially in bright sunlight and warm weather.

As a result, authorities in the eastern French city of Strasbourg lowered bus fares and bicycle rental fees in the hope of discouraging peope from using their cars.

In Portugal, where ozone levels were consistently at dangerous levels for more than a week at the end of July, authorities recommended that the elderly and those with breathing difficulties remain indoors.

Occasionally dangerous levels of ozone in Austria led the authorities to ask people to think twice about using their cars.

Despite unusually high levels of ozone in Belgium, Environment Minister Freya Van Den Bossche said that speed restrictions on motorists were an inefficient measure to impose.

However, drivers in neighbouring Luxembourg were asked as of last week to stick to 90 kilometres (60 miles) an hour on the Grand Duchy's motorways instead of the usual 120. Parts of Switzerland imposed similar restrictions on motorists.

In Spain, authorities in Madrid saw ozone rise to its consistently highest level in four years.

But the European ozone anomaly was Britain, where the highest recorded level of ozone was less than half that reached in 1976, the year of Europe's greatest recent drought.

With often cloudy skies, pollution levels recorded Wednesday showed England and Wales as "moderate" and Scotland as "low".

TERRA.WIRE