Ozone smogs are costing Europe's farmers more than six billion Euros a year, according to the most detailed assessment to date.
The biggest losses are suffered by France at more than 1.5 billion Euros and Germany at approaching 1 billion Euros. Britain gets off comparatively lightly with a loss calculated at around 200 million Euros, tenth in the league table covering 45 countries of Europe and the former Soviet Union.
"The losses are certainly significant. They represent several percent of annual production for some countries," said the lead author of the study, Mike Holland of AEA Technology, Culham, UK.
The study was carried out by British scientists for the UN Economic Commission for Europe, which oversees a series of international treaties to control air pollution on the continent. Other countries badly hit by ozone damage include Spain, Italy, Poland and Ukraine.
Ozone in the upper atmosphere protects the planet from ultraviolet radiation. But close to the ground it is a dangerous toxin. It is one of the most dangerous components of smogs, and is created in photochemical reactions involving nitrogen oxides and hydrocarbons emitted in vehicle exhausts.
Cruel irony
Ozone levels are highest in the summer, when crops are growing, and in southern Europe, where high temperatures make the photochemical reactions most intense. By a cruel irony, ozone levels are often also highest in the crop-growing countryside surrounding urban areas. This is because ozone takes several hours to form and complex reactions in the immediate vicinity of vehicle emissions can prevent its accumulation there.
Typical modern air over Europe in the summer is toxic to many crop plants, but not all. France's vineyards are untroubled, but its wheat, potato and legume fields are. The study found that, across Europe, a third of the cash value of lost crops came from wheat and a further fifth from potatoes.
"One big gap in the study is the effect of ozone on grass pastures," says Holland. He thinks that this could add as much as four billion Euros to the bill, through lost meat, milk and cheese production. "But that is very a much a back-of-the-envelope calculation. Nobody has put up the money for a proper study," he told New Scientist.
European air clean-up targets for 2010 could reduce the losses by as much as a third, the study finds. But the benefits will be variable. British benefits could be only a twentieth as much as the gains for French farmers.
Fred Pearce