The commentary on Oct 8 ("Official one-hour PSI figures, please") said that "on a day when PM2.5 levels hit 100mcg per cubic metre, a person will take in around 1,100mcg of these pollutants if he stays outdoors throughout the day. This is much less than the amount of PM2.5 pollutants a smoker will inhale for every cigarette consumed, which is in the range of 10,000mcg and 40,000mcg".

While this analogy is presumably meant to provide some reassurance that inhaling pollutants as a result of the haze is not as hazardous to one's health as say, smoking, one may wish to temper this view.

After all, it is well known that one does not have to be a smoker to be at risk of lung cancer.

Air pollution, particularly second-hand smoke, is a significant risk factor as well, and second-hand smoke can raise the levels of PM2.5 pollutants by many times in a localised environment.

Furthermore, while one has the option of steering away from people who are smoking, the same cannot be easily said of the haze which permeates all outdoor areas and, over time, makes its way indoors as well.

Finally, the levels of PM2.5 pollutants encountered in the current haze have far exceeded the 100mcg per cubic m cited above.

Indeed, levels in the hazardous or very unhealthy range have been repeatedly observed and, after suffering such a prolonged haze, it is almost welcome news if the PSI (which incorporates PM2.5) hovers around 100.

Framed in this perspective, I hope the authorities can exhaust all means to prevent such a haze episode from ever happening again.

As residents of a First World country, it is a basic expectation that we should have clean, First World-quality air all year round.

Daniel Ng Peng Keat (Dr)