"Absence of lead does not imply increased benzene content and therefore it is incorrect to presume that unleaded fuel will lead to higher benzene emission", Dr K Kumar, chairman, technical committee of Association of Indian Automobile Manufacturers (AIAM) said here on Thursday.

Benzene emmission, however, can be significantly lowered through the use of a catalytic converter which breaks benzene down into carbon dioxide and water, Kumar said adding that the combination of unleaded fuel and catalytic converters will lead to least vehicular emission.

On the issue of unleaded petrol requiring catalytic converters, the AIAM said it was rather the other way around. A catalytic converter required unleaded petrol, because lead poisons catalyst.

"Unleaded petrol of adequate octane quality (87 RON), can be used in any vehicle, old or new, with or without catalytic converter", AIAM said.

AIAM said that catalytic converters are necessary as they convert benzene to carbon dioxide and water and also reduce carbon oxide and hydro carbon emissions.

But this does not mean that without installing the converters, unleaded petrol cannot be used, it said. On the concern expressed that use of unleaded petrol will reduce the engine life, Kumar said it is lead which causes engine wear.

Presence or absence of lead alone does not effect knocking in the vehicle, he said adding it was octane number of fuel which affects knocking. If octane number of unleaded petrol is same or higher, there is no question of knocking, Kumar added. The association said that introduction of "green fuel" in Delhi was just a first step towards meeting the stringent pollution norms for the year 2000.