As the owner of a private diesel vehicle, I was concerned to read that the Government is reviewing its emissions policy to discourage the use of diesel vehicles ("Clearing the air on diesel"; Jan 28).

Any regulatory measure needs to be carefully thought through and a long-term view taken.

The Ministry of the Environment and Water Resources should consider several principles.

Targeting private diesel vehicles will not move the needle much in terms of reducing pollution.

There are about 189,200 diesel vehicles in Singapore, as of December last year.

Of these, just 10,364, or 5.5 per cent, are private vehicles.

Most of them already follow Euro V or VI standards, and also average much lower mileage than commercial vehicles, taxis or buses.

It would be more impactful to review the early turnover scheme for buses and commercial vehicles, which number over 155,000, or to promote the conversion of the 23,750 diesel taxis to hybrid or electric vehicle technology.

Most owners of private diesel cars made the switch in 2012 when the Government was promoting diesel vehicles as a greener alternative.

We understand that, in view of the updated understanding on the pollutive effects of diesel, there is a justifiable concern about the growth rate of private diesel vehicles.

One way to slow this down is to have a one-time pollution surcharge placed on new owners of diesel cars.

This will not negatively impact existing owners of diesel cars who bought their vehicles on good faith, based on the information available and government policy at the time.

It is important to recognise that science is evolving.

To revise policies abruptly upon the availability of new information is not optimal. If the public perceives that the risk of abrupt policy shifts is high, it may have an adverse impact on the adoption of green technology in future.

Danny Lim Fung Yee