Lead compounds were introduced into petrol in the US in 1923, and universally only in the seventies to neutralise engine knock, which afflicted high-compression ratio engines, which were manufactured to increase mileage.

But subsequently it was discovered that even low levels of lead in the atmosphere can cause low IQ levels in children and irreversible brain damage. Lead degrades even soil and vegetation, and increases concentration of air pollutants like oxides of sulphur, nitrogen, unburnt hydrocarbons, carbon-dioxide and carbon monoxide.

So leaded petrol was out. And unleaded petrol was in along with catalytic converters, which render alternative anti-knock additives, like aromatics, olefins and oxygenates,harmless. If untreated, these additives have been reported to be health hazardous and causing cancer, anaemia and thrombocytopenia.

But even the use of a catalytic converter isn't enough in itself. It functions optimally only at a minimum operating temperature. The converter doesn't function during a short drive because it doesn't warm up sufficiently. Besides, it's difficult to say when a converter is not functioning properly, which is worse than not using one because a defect increases the exhaust pollutants manifold. Vehicles fitted with converters require proper tuning of the fuel-air ratio so that the engine doesn't misfire. The catalyst get damaged by overheating.

Surprisingly, the government announcement is silent on the issue of catalytic converters. Instead the Association of Indian Automobile Manufacturers has issued a statement adding that the use of unleaded petrol in vehicles without catalytic converters would not affect their engines adversely. The ideal requirement is that vehicles usingunleaded fuel should be equipped with catalytic converters to treat tailpipe emission, though.

Evidently, universalising the use of unleaded petrol is at best an ad-hoc measure because it's neither environmental friendly in itself nor economical. It's sold at the same price as leaded fuel. It's costlier to process, though. Besides, it emits all the toxins of leaded petrol except lead.

The solution lies in an alternative fuel. Worldwide nearly 10 million vehicles are run on ethanol, propane, compressed natural gas (CNG), natural gas and methanol. Besides vehicles are operated by electricity and batteries. But in India, most of the 32 million vehicles are run on petrol or gasoline.

Amongst the alternative fuels only CNG has been introduced in the country. But it's available only in select pockets. This despite the fact that CNG is preferable to even unleaded fuel. It contains few harmful emissions, and costs less than half of petrol. Only the vehicle needs to be fitted with a bi-fuel conversion kit, whichcosts from Rs 32,000 to Rs 35,400.

Fuels like ethanol, propane and methanol are yet to arrive in India. Though essentially used to enhance octane, methanol can be used as a fuel on its own. But its energy content is only one half of gasoline. Ethanol is not the best choice either because it produces less energy than it consumes for its production. Nevertheless their consumption as a vehicle fuel produces few harmful emissions.

The most promising alternative fuel worldwide is propane. It's low on toxins, and costs one-fourth of petrol. Efforts need to be intensified on war footing to develop and market this alternative fuel on a mass scale. Particularly since vehicular pollution is the major source of air pollution in our country. Of the total air pollution, vehicular pollution contributes 64 per cent in Delhi, 52 per cent in Mumbai and 30 per cent in Calcutta. Gigantic problems demand matching responses. Not half-hearted symbolic measures.