In the 2005 annual survey by the Political and Economic Risk Consultancy (PERC), Singapore scored particularly well for our air quality. In another survey by ECA International, Singapore was ranked first, beating nine other cities as the best place to live in Asia. In fact, we came in an impressive third out of 250 locations worldwide. One of the reasons? Good air quality. This comes as no surprise given that 88 percent of the days in 2005 were rated "good", while only 12 percent were moderate under our measure of air quality, the Pollutant Standards Index.

The Invisible Killer
Its easy to take the clean air we have in Singapore for granted. It's a happy problem that's not starkly visible and obvious as we go about our everyday lives. Though our air quality is good, there's an annoying smudge in this pretty picture – PM2.5, a fine pollutant that is linked to asthma, bronchitis and other respiratory problems. Its particles are so small that they can penetrate deep into our respiratory tract, and at high levels, is a real health hazard, especially among children, the elderly and those with cardiovascular or chronic lung diseases.

The average level of PM2.5 in our air was 21 ug/m3 in 2005 – exceeding the international accepted standard of 15 ug/m3 set by the US Environmental Protection Agency (USEPA). Fifty percent of this invisible pollutant is contributed by diesel vehicles. With more of such vehicles on the road, expect the levels of PM2.5 to increase too if nothing is done to curb it.

Attacking the Problem
Currently, there are approximately 149,000 diesel vehicles here. That's a whopping 20 percent of Singapore vehicle population contributing to PM2.5 levels in our ambient air. So if diesel vehicles are the main culprit, then diesel vehicles are the target for change.

That's why the Ministry of Environment and Water Resources (MEWR) announced the adoption of stricter Euro IV emission standards for diesel vehicles from 1 October 2006. Euro IV diesel vehicles need "clean" diesel with ultra low sulphur content to operate optimally. According to NEA Director-General of Environmental Protection Loh Ah Tuan, "It has been estimated that PM2.5 emissions from Euro IV diesel vehicles are 70 percent lower than those from existing Euro II vehicles." The aim was to lower our PM2.5 levels to within USEPA standards by 2014.

In conjunction with the adoption of Euro IV emission standards, Ultra Low Sulphur Diesel (ULSD) was introduced with effect from 1 December 2005 to pave the way for Singapore to adopt the Euro IV diesel vehicles. The fuel contains under 50 parts per million sulphur, one-tenth of the conventional diesel. Before the 1 December 05 deadline, Shell became the first oil company to introduce this new grade of diesel at five stations in Singapore in June 2005, offering it at no additional cost to motorists. ULSD has since replaced conventional diesel at all service stations in Singapore.

In recognition of the lower emissions of Euro IV compared with Euro II vehicles, the Government lowered the special tax from six times to four times the road tax as of January 1, 2006. However, Euro IV vehicles still emit more PM than petrol or CNG cars.

That's not to say that the petrol cars are not culprits too, in contributing to air pollution. They release their fair share of pollutants. (See box story "Best of both worlds" for more details).

So how about using another form of environmentally-friendlier fuel? That's precisely the strategy chosen to lower vehicular emissions – to encourage more companies and individuals to adopt compressed natural gas (CNG) vehicles instead. CNG vehicles emit negligible amounts of particulate matter, as well as lower levels of other air pollutants and carbon dioxide compared to petrol vehicles. That means cleaner air for everyone.

To encourage taxi and bus operators to switch early to Euro IV compliant vehicles, the government also announced a tax incentive package for CNG and Euro IV taxis and buses. Under the package, CNG and Euro IV taxis could enjoy an ARF rebate of 80 percent of the vehicle's Open Market Value (OMV) from 1 January to 30 September 2006, and 40 per cent OMV from October 2006 to 31 December 2007. Euro IV diesel or CNG buses would be completely exempted from paying the Additional Registration Fee of 5 percent of the OMV till 31 December 2007.

And that's not all.

The Government announced that CNG taxis will continue to be exempted from the special tax until December 2007. In addition, the recent enhancement of the Green Vehicle Rebate from 20 percent to 40 percent applies to all hybrid cars, including CNG ones.

One taxi company taking full advantage of the green car concessions is SMART Automobile. Last December, together with Daimler Chrysler, the cab company rolled out Singapore's first fleet of 100 commercially-run Mercedes-Benz CNG-petrol bi-fuel E200. The bi-fuel cars give SMART drivers the flexibility to run on petrol should the vehicle run out of CNG.

Given these rebates, it costs SMART only about $5,000 more to register each Mercedes-Benz E200 NGT (Natural Gas Technology) than that of a Euro IV E220 diesel taxi despite the fact that the more environmentally-friendly model has a much higher open market value (OMV). (More details in box story).

Clean air is not free
The flag down rate of these CNG cabs will set you back 40 cents more, $3 instead of the usual $2.60 compared to other Mercedes-Benz cabs. It also costs a fair bit more to own one of the currently-available hybrid cars on the market compared to conventional ones in a comparative class.

But, perhaps the real question to ask is this: Which would you prefer to pay for – cleaner air or you and your famiy's medical bills? As Chairman of NEA, Assoc Prof Simon Tay said at the launch of Shell's Ultra-Low Sulphur Diesel in September 2005, "Just as we pay for water and for oil, the natural resource of clean air is also not free. By "paying" for clean air, we can avoid paying in terms of harmful effects to our health. Paying for clean air also underwrites the life of our city. More Singaporeans are embracing an outdoor lifestyle, whether going to the beach or park for exercise and outings, strolling down Orchard Road, or eating in sidewalk cafes or hawker centres."

All things considered, given the pace of technology and the rising cost of fuel, it might make more sense (and cents) to switch to a more environmentally-friendly mode of transport in the near future. We'll even be able to breathe better for it too.