UNLEADED petrol is being touted as a green fuel. But it does more harm than good if vehicles using it do not have catalytic converters to render the exhaust gases safe, according to Roger Perry, professor of environmental control at the Imperial College in London (New Scientist, Vol 140, No 1899).

In unleaded petrol contains aromatic hydrocarbons instead of lead compounds for better combustion and less carbon monoxide emission. However, Perry found the higher the aromatic content of the fuel, the higher the emissions of carcinogens such as benzene, toluene and xylene from vehicles without catalytic converters. Perry says the risk from these emissions is greater in developing countries, where refineries produce poor quality petrol, which has to be improved with the use of additives.