TWO years of lead-free petrol pouring from pumps has done nothing to improve air quality in Hongkong, which Government officials say exceeds safety limits by at least 30 per cent. Car owners keen to go green began using unleaded petrol when it was introduced in April 1991, and sales of the fuel peaked in February this year. But environmental protection officer Mr Raymond Leung Pak-ming said their environmentally friendly gesture was an empty one. Diesel vehicles still make up more than 70 per cent of traffic and emit about 80 per cent of pollutants. So the benefit from the small number of cars using lead-free petrol has been swallowed up in a haze of black smoke. A controversial Government proposal to switch vehicles from diesel to unleaded petrol, which was shelved two years ago, is being resurrected in an attempt to clear the smog. But even Environment Protection Department (EPD) officials admit this will do nothing more than maintain air quality at the present dangerous levels, because any reduction in diesel pollution will be wiped out by the predicted doubling of road traffic bythe year 2000. Both the EPD and Friends of the Earth (FoE) have called for stricter controls on traffic, and say it is the only answer to Hongkong's air pollution problems. The Environmental Pollution Control Committee is to study a paper tomorrow on how to control traffic pollution, while the proposed diesel to petrol switch will be discussed in the next month. The EPD claims the switch to lead-free petrol is the only way to control cancer-causing black smoke emissions from diesel vehicles, and has revised the cost of implementing the proposal to push it through. If it is not approved, experts warn air pollution will increase dramatically. The EPD, however, says the fuel switch will only improve air quality if it is introduced overnight, before the volume of traffic increases. The scheme, which would affect taxis, public light buses and possibly light goods vans, would have to be phased in over several years. All new vehicles would have to be fitted with catalytic converters, which reduce dangerous emissions, and be fuelled by lead-free petrol. ''The scheme will just keep the situation from deteriorating,'' said Mr Leung. ''We won't see any significant improvement unless something is done about vehicle growth. ''The Government should be looking at transport, to plan and manage the demand, and perhaps take up some of the growth in other ways, like extending the MTR network.'' Environmental protection officer Mr Kong Ha said: ''Unleaded petrol was only introduced as a first step, to allow for the introduction of a switch from diesel to petrol. But further measures are necessary if pollution is to be reduced.'' FoE spokeswoman Ms Lisa Hodgkinson also called for stricter transport controls: ''Catalytic converters are not efficient in Hongkong's urban traffic conditions, and while the use of unleaded petrol is a good thing, it is not enough to change Hongkong's traffic pollution problems.'' But the Transport Department's Assistant Commissioner, Mr Chan Chin-chun, said current Government policy covered management of road use and improvements in public transport to reduce traffic. He said a system limiting the number of vehicles on the roads would be difficult to introduce and was not an option.