A number of carmakers and dealers are crying foul over a surprise move to exempt some models from getting particulate matter (PM) readings. It is counterproductive to the Government's aim to reduce PM - or fine soot - in the air, they said.
The National Environment Agency (NEA) made public last week, in response to queries from The Straits Times, that petrol models with port fuel injection (PFI) will not be tested for one of the five pollutants.
The news came two months after the NEA announced a new car emission scheme that takes into account five pollutants, including PM.
The NEA said petrol models with PFI - where fuel is injected just before the engine's combustion chamber - will not be measured for PM when the Euro 6 emission standard kicks in in September, and when the Vehicular Emissions Scheme (VES), which dishes out tax rebates or surcharges according to a car's emission levels, starts in January.
It explained that the European Commission makes a similar exemption for PFI models, citing the PM emissions from these models as being "very low".
Because of this exemption, a car like the Toyota Corolla Altis, which employs PFI, could enjoy a tax rebate, while a similar model, such as the Mazda 3, would be slapped with a surcharge. This could make the Mazda 15 per cent to 20 per cent costlier than the Toyota.
Sales director David Pang from Alpine Group, which sells Opel and Chevrolet cars, said: "We have no quarrels with the timeline for the new emission standards. But exempting one group of vehicles from what is a key pollutant count will just create unfair competition."
Meanwhile, PFI technology is deemed to be less fuel-efficient and could produce more carbon dioxide than direct injection, where the fuel is sprayed directly into the combustion chamber.
Mr Pang added: "The latest and more efficient engines are measured for attributes that older, less efficient engines are not. This will lead to the more efficient engines being penalised by the VES."
Audi Singapore managing director Jeff Mannering said: "The reason behind VES is to raise standards to ensure Singapore has the most efficient and environmentally friendly standards available in the world. However, allowing a port fuel injection to be exempted from PM readings makes no sense.
"Every car should be measured the same way."
A spokesman for BMW Group said: "We cannot confirm that port fuel injection always tends to produce less particulate emissions. This depends very much on the engine load."
He added that under high engine load, such as accelerating from a stop or overtaking, "the particulate emissions of engines with direct injection can be equal or even lower than those with port fuel injection".
A 2012 European Commission study concurs and said there are concerns regarding the suitability of the legislated procedure for the assessment of the true particulate emissions of PFI vehicles. "The particle number emissions of PFI vehicles are found to strongly depend on the driving behaviour," it read.
Asian Clean Fuels Association director Clarence Woo said no exemption should be made as emission standards should be "technology neutral".
National University of Singapore transport researcher Lee Der-Horng said: "Regarding exhaust emission... it may not be a good choice if we wholly rely on European standards, since the actual emission performance varies (with) many other factors."
