Letter: Pollution and the diesel debate

Sir: Shauna Massey's article 'The jury on diesel is not yet closed' (18 October) came to the right conclusion - that the environmental debate between diesel and petrol is too close to call, and that poor maintenance contributes the majority of pollution. But in doing so she seems to have made two quite serious mistakes.

The first is where she says that lead was replaced by benzene when unleaded petrol was introduced. The lead in petrol is there to increase its octane.

But unleaded premium petrol has a lower octane number than leaded 4-star, so there was no need to replace it with benzene or anything else.

In fact, unleaded petrol now contains less benzene than leaded petrol did in 1986, the year when unleaded petrol was first introduced into the UK.

Incidentally benzene is produced in the refining process, it is not added as an optional extra to petrol.

Second, although diesel engines do give off less carbon dioxide, not even their most enthusiastic supporter would claim this is only a third of what the equivalent petrol engine emits. It is generally accepted that a diesel's carbon dioxide performance is 10-30 per cent better than a petrol engine.

Sincerely, DAVID PARKER Director General Petroleum Industry Association London, WC2 18 October