Britain is ignoring the dangers posed by one of the world's worst air pollutants: ozone. Researchers say that levels of the gas - a powerful contributor to global warming and the cause of hundreds of deaths a year from respiratory illnesses - are rising at an alarming rate.
They have also warned that measures to curtail the gas are failing. As a result, ozone-related deaths, of which there are about 1,500 a year in the UK, could rise by 50 per cent over the next decade. Stronger international treaties need to be set up to counter the threat, they insist.
'A lot more interest needs to be taken in ozone - not only as a cause of global warming but as an immediate threat to human health and to the environment,' said Professor Piers Foster of Leeds University, an author of the most recent report from the Intergovernmental Panel on Climate Change. 'It could have a significant impact on the planet.'
Ozone is produced by the impact of sunlight on atmospheric pollutants, including car exhausts, and is strongly associated with smogs caused by traffic fumes. Hot summers, in areas polluted with nitrogen oxides and volatile organic chemicals (VOCs) emitted by vehicles, produce peak levels of ozone. Unlike ozone in the stratosphere, which protects Earth from harmful ultraviolet radiation, ozone in the lower atmosphere is harmful to humans, animals and plants.
The EU has introduced measures to reduces these pollutants, mainly by ensuring three-way converters are fitted to cars, and this has helped reduce ozone production in Europe. But countries such as Russia, China and India are still major emitters, and ozone from these nations is constantly being blown over Britain. As a result, levels are continuing to rise at a rate of 6 per cent per decade.
'The trouble is that ozone production is controlled by a patchwork of local laws and regulations,' said Professor David Fowler of the Centre for Ecology and Hydrology, Edinburgh, leader of a recent Royal Society working group on ozone. 'Weather systems and jet streams transport ozone and the pollutants that trigger its production far from its point of origin. In addition, shipping is a major producer.
'So you could introduce all sorts of measures to cut down local emissions, but these reductions would be overwhelmed by the ozone and the nitrogen oxide pollutants being swept over the country from marine and from foreign sources. Until we get an integrated network of international agreements in place, we will never get round the problem. At present no efforts are being made to set these up, however.'
Rising production of ozone is alarming because the gas is the third biggest contributor to global warming. Only carbon dioxide and methane have bigger impacts. But unlike them ozone also affects health. It is a powerful oxidant and damages lung tissue. In 2003 it caused more than 1,500 deaths in the UK - mainly among children and the elderly - and that figure is set to rise to about 2,400 a year by 2020.
In addition, the gas has a serious impact on the ecology. Ozone enters plants through respiratory pores in their leaves and harms their ability to photosynthesise foodstuffs. Plants are left weak and undersized. It is estimated that in 2000, ozone caused £5bn damage to crops in Europe, a figure that is rising by the year.
Even worse, trees and vegetation damaged by ozone cannot properly absorb carbon dioxide and the gas therefore has a double impact on the climate: it helps raise the temperature of the atmosphere and it hinders the planet's ability to cope with other greenhouse gases. Thus limiting ozone production should be given greater priority, a point stressed by Professor Peter Cox of Exeter University.
'We estimate that these effects on plants could double the importance of ozone increases in the lower atmosphere as a driver of climate change,' he said. 'So policies to limit increase in ozone must be seen as an even higher priority.'
The danger hole
Ozone is harmful at sea level but in the stratosphere, six to 31 miles high, it forms a protective layer which blots out the sun's powerful ultra-violet radiation. In 1985, scientists discovered a growing hole in this layer over Antarctica which had been caused by made-made chemicals in the atmosphere. Bans on these products should close the ozone hole, but not until 2060.