THE company selling the oxygen canisters claims on its website that in a country like Singapore where most people are city dwellers, the air contains 'high levels of harmful pollutants'.

-- ST FILE PHOTO

These are said to be carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter and sulphur dioxide.

However, a spokesman for the National Environment Agency (NEA) stresses that the air quality in Singapore is good.

It meets all the parameters of the United States Environmental Protection Agency's (USEPA) national ambient air quality standards, except for PM2.5, or particulate matter that is equal to or finer than 2.5 microns.

Particulate matter is a complex mixture of extremely small particles and liquid droplets like acids and organic chemicals.

The average PM2.5 level here last year exceeded the USEPA recommended safe level by about 50 per cent.

To bring down the levels of PM2.5 to within USEPA standards, the NEA introduced the stringent Euro IV emission standards in October last year for diesel vehicles, as they are responsible for around 50 per cent of the total PM2.5 emissions here.

The PM2.5 readings were also affected by the haze from the forest fires in the region.

The NEA expects the new standard to help Singapore achieve safe PM2.5 levels by 2014.

Mak Mun San