Letter: Benefits of a cat under the bonnet

Sir: Gavin Green ('The many ways of killing a cat', 2 January) perpetuates several of the myths about catalytic converters, which are being fitted to all new cars from 1993.

Even if converters were as sensitive to leaded petrol as Mr Green states, it is very difficult to accidently put in leaded petrol instead of unleaded. This is because the wider nozzle of a leaded petrol pump will not fit inside the narrow filler of a catalytic converter- equipped car. This means that leaded petrol cannot be put in by mistake because the flap that lets fuel in does not open.

Several tankfuls of leaded petrol are needed to completely wreck the performance of a catalytic converter. One tankful, which is not recommended, would cause a short-term reduction in pollution control but most activity would be recovered on returning to the use of unleaded petrol.

Mr Green is also wrong on the effects of high mileage. In the United States, where catalytic converters have been in widespread use since 1975, the regulations state that cars have to be demonstrated by the manufacturer to meet the pollution limits imposed after 50,000 miles. This is now being extended to 100,000 miles in recognition of the improvements in catalyst and engine technology that have led to better system durability.

Good and regular services and emissions checks are an important part of ensuring that cars (catalyst and non-catalyst) do not cause unnecessary pollution. However, tests that we have organised on a fleet of 25 cars with an average age of 40,000 miles show that pollution at this point is still 25 per cent below the levels set by the new regulations.

At 100,000 miles the catalytic converter will still work, provided the engine is well maintained, although pollution levels will rise as engine and systems age. The good news is that with the use of controlled fuel injection and advanced engine management systems the untreated pollution from engines is lower than the pollution from the carburettor engines that the new systems are replacing - adding a catalytic converter then reduces pollution by a significant further amount.

Yours faithfully,

R. A. SEARLES

Market Development Director

Johnson Matthey Catalytic

Systems Division

Royston,

Hertfordshire

5 January