Win some, lose some

Catalytic converters, lauded for reducing pollution, may in fact produce large quantities of ammonia, claim researchers in America.

Catalytic converters, lauded for reducing pollution, may in fact produce large quantities of ammonia, claim American researchers.

The research, headed by Professor Robert Harley of the University of California – Berkeley, found unusually high levels of ammonia in vehicle exhaust emissions.

The research found that the likely cause was catalytic converters, although engines that are not properly tuned can also contribute to ammonia emissions.

The problem, according to Harley, may be caused by catalytic converters working too well.

If nitrogen oxide from an engines exhaust is ‘over reduced’ a complex chemical reaction occurs: ammonia gas forms in the catalytic converter, which is then emitted from the exhaust pipe.

Professor Harley’s team used air particle sampling to measure ammonia and other emissions from over 60,000 vehicles passing along a California highway tunnel over an eight day period.

They found that the typical car emitted 0.28 ounces of ammonia, roughly one teaspoon full, per hundred miles.

The researchers note that their study included more vehicles with hi-tech pollution controls, which are used with low-sulphur reformulated petrol, than in previous studies.

The US Environmental Protection Agency have identified ammonia particles for regulation under the Clean Air Act on the grounds that they may endanger human health.