Concentrations of the corrosive gas at levels known to affect lungs have become common during still, sunny summer days.
The Government's Photochemical Oxidants Review Group (PORG) said pollution control measures to which Britain and other European Union nations have signed up are insufficient to meet air quality targets for ozone and other pollutants by 2000. More will have to be done, especially to curb fumes from car exhausts.
The ozone in the stratosphere shields the Earth from much of the Sun's harmful ultraviolet radiation. But at ground level the gas is a highly corrosive pollutant.
It is created in a complex series of chemical reactions that need sunlight and other air pollutants - the oxides of nitrogen and hydrocarbons produced when coal, oil and gas are burnt.
Ozone levels peak in summer because there is more sunshine. They are also higher in the countryside because nitrous oxide, an abundant pollutant in vehicle exhaust, destroys ozone in the short term even though exhaust fumes are the major contributor to low-level ozone overall. Nitrous oxide concentrations are highest in the cities.
Ozone levels are also raised on high ground, so the worst ozone pollution is often found on Britain's remoter mountains and uplands.
The PORG report is based on measurements from 46 recording stations around the country in the late 1980s and early 1990s. The scientists conclude that ozone levels have been rising by about 3 per cent a year and are now double the levels found a century ago.
Nearly one-third of the population lives in places where the ozone level has been 90 parts per billion for at least 20 hours in the year - an air quality safety limit for both the World Health Organisation and the European Union. Much of England and the uplands of England and Wales are included.
This 90 ppb level is known to affect lungs, reducing the efficiency with which they take oxygen into the bloodstream, especially when people are doing heavy exercise. Some people may be affected at lower levels of 60ppb. What is not yet known is whether exposure to ozone at these levels causes lasting damage, although it appears that one in ten of the population is particularly sensitive. Rising ozone pollution may be associated with the increase in asthma cases.
Ozone affects some crops and species of wild plants at much lower levels, down to 40ppb. PORG estimates that harvests are being reduced by many millions of pounds each year. Ozone also corrodes materials such as rubber, paint and plastic.
Catalytic converters are now compulsory on all new petrol cars and a second generation of pollution-abatement equipment for vehicles will become compulsory in 1996. Even so, the scientists say further anti-pollution policies are needed.
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