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WhyItMatters

Clearer picture of haze risk

Earlier this week, the National Environment Agency (NEA) introduced new bandings and descriptors for the one-hour concentration readings of fine particles called PM2.5- a major pollutant in smoke haze.

While one-hour PM2.5 concentration readings have been available since 2014, the new bandings will help people plan their immediate activities.

They state which levels of one-hour PM2.5 concentrations are considered normal or very high, and will especially help vulnerable groups such as the elderly, pregnant women and those with asthma.

The 24-hour Pollutant Standards Index (PSI) and three-hour PSI take into account six pollutants including PM2.5 but they are averaged out over the given periods.

PM2.5 pollutants are of concern because they are smaller than 2.5 microns in diameter, or a 30th of the diameter of a human hair.

Due to their size, the human body cannot filter them out. Long and regular exposure to the pollutant is linked to higher risk of death from complications such as lung cancer or heart disease.

The move to introduce bands and descriptors comes after members of the public suggested having a guide to PM2.5 readings after last year's haze episode.

Unlike the 24-hour PSI, however, the new bandings will not come with health advisories.

The NEA has said that this is because there is not enough evidence to show the health impact of short-term exposure to PM2.5 particles.

Nonetheless, the new bandings are a step in the right direction.

As Associate Professor Richard Webster from the Nanyang Technological University's School of Physical and Mathematical Sciences put it: "The new descriptors are useful in planning exercise regimes or when you know you are going to be breathing heavily. As much as possible, we should engage in heavy physical activity when the PM2.5 concentration is low."

Carolyn Khew

A version of this article appeared in the print edition of The Straits Times on July 01, 2016, with the headline 'Clearer picture of haze risk'. Print Edition | Subscribe