There is only one way to clean up the exhaust emissions of cars quickly, and it has nothing to do with insisting that new vehicles meet tighter limits. Legislation mandating the introduction of electric cars - set to happen in California by 1998, and being considered by some city authorities in Germany and Switzerland - is not the answer, and neither are incentives to get 10-year-old cars off the road, as has happened in France and Spain.

No, the solution is much simpler - so simple that it has eluded the Government, environmental groups and most of the car industry. Namely: if you don't want poison in the air, don't pump poison into your car's fuel tank. Cleaner petrol would bring about a significant improvement in air standards instantly.

As usual when it comes to emissions legislation, the Americans are leading the way. At the beginning of this year, "reformulated gasoline" (RFG) became compulsory in major cities where air standards have failed to meet levels set by the Environmental Protection Agency. These include New York City, Los Angeles, Chicago and Houston. Other areas have chosen voluntarily to embrace RFG, including the states of Massachusetts, Connecticut and Delaware, as well as Washington DC. It is estimated that during 1995, one-third of petrol sold in America will be RFG.

Overall, RFG will probably reduce toxic emissions from cars by 15 per cent. It also reduces urban smog, and offers the same improvement on old bangers as on modern, catalyst-equipped cars. No other single action could bring such a large reduction in pollutants. In 1999, when a new, tougher blend of RFG is released, emissions would be cut by 25 per cent.

RFG works in a number of ways. First, and most important, it evaporates less easily. One of the major contributors to atmospheric pollution in cities is fuel vapour that escapes from the fuel tank as the car is being driven, parked or refuelled. These unburnt hydrocarbons are now regulated as exhaust emissions, and catalytic converters kill off most of them. But there is no strict regulation on them when they escape from fuel as vapour.

Many toxicologists, including Dr Simon Wolf of the University of London, agree that escaping vapours are more deadly than exhaust emissions. The most deadly hydrocarbon of all is probably benzene, a known carcinogen. America's new RFG fuel is not only about 30 per cent less likely to evaporate, but it also has a maximum of 1 per cent benzene. Petrol sold in the EC has a maximum benzene level of 5 per cent.

Experts say that the new RFG fuel is likely to reduce total vehicle-produced hydrocarbons, both from exhaust emissions and evaporation, by about 60 per cent when the outside temperature is 24C. The higher the temperature, the greater the improvement, because fuel vaporises more easily in hot weather.

RFG, when burnt by the engine, also gives out fewer exhaust hydrocarbons and less carbon monoxide, owing to a small amount of oxygen in the fuel. About 2 per cent of RFG is oxygen. "Oxygenated" fuel is already common in the some US states, owing to its cleaner burning properties, and there have been some moves by small oil companies to have it introduced in Britain, without success.

RFG, however, costs more to make. Motorists will have to pay about an extra seven cents a gallon in America. Were RFG to come to Britain - and almost every American emissions initiative does sooner or later - it would cost even more, owing to our higher fuel taxes. Fuel economy is also affected: cars use 2-3 per cent more RFG over a given route than they would conventional petrol.

RFG is significant not just because it is cleaner, but also because it represents the harshest regulation inflicted so far on the oil industry by a government. The responsibility for cleaning exhaust emissions has hitherto rested largely with the car makers. As a leading anti-lead campaigner, Professor Derek Bryce- Smith, from Reading University, once told me: "The car firms are either too stupid, or are simply unwilling, to kick up a fuss. The oil companies can't believe their luck." Usually , when thepetrol companies advertise "cleaner" petrol, they mean cleaner for the engine, not for the atmosphere.

So why are the oil firms suddenly playing the good guys in America? Back in 1989, one of the big car makers, General Motors, broke rank and accused the oil industry of slothfulness. In a speech to a petrol industry group, Joseph Colucci, of GM's researchwing, told the audience to clean up their products. "If we don't want certain compounds in the air, then we shouldn't put them in our tanks," he said Such accusations by the world's biggest car company stung. The oil industry moguls could begin to see their domination in vehicle fuels under threat. In America, blended fuel - a mixture of petrol and either methanol (usually made from natural gas) or ethanol (usually made from corn) - was becoming increasingly popular because it pollutes less. Unless theoil companies cleaned up their products, market share would slip away. RFG is the result.

Although there is no imminent threat to the oil industry from alternative fuels here, and even though our Government is amazingly dozy at implementing new emissions legislation (we introduced catalytic converters 20 years after the Americans), some sort of cleaner, reformulated petrol is inevitable in Britain.

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