1-hour PSI: NEA creates bands to simplify PM2.5 readings

Descriptors for one-hour readings will help the public understand figures, plan activities
By Carolyn Khew, The Straits Times, 28 Jun 2016

The National Environment Agency (NEA) has introduced bands and descriptors for one-hour concentration readings of fine particles called PM2.5 to help the public make sense of the readings and plan their immediate activities.

While the agency has been publishing such one-hour readings since 2014, it is now providing breakdowns of what constitutes normal to very high levels of one-hour PM2.5 concentrations.

For instance, the range of 0 to 55 micrograms per cubic metre (mcg/m3) is described as "normal", while anything above 250 mcg/m3 will be described as "very high".

The Straits Times understands that the bands and descriptors were introduced after members of the public suggested having a guide to PM2.5 readings after last year's haze episode. Still, the bands do not state what levels are healthy or not, unlike the 24-hour Pollutant Standards Index (PSI), which is used by the authorities here as the reference for health advisories.

Minister for the Environment and Water Resources Masagos Zulkifli, who made the announcement yesterday, said there is "no strong medical study" to show the impact of short-term exposure to PM2.5 particles on one's health.

"In any case, if you are sensitive to such particles, or you have some form of ailment that makes you sensitive to such particles, consult your doctor," he added.

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

It is one of six pollutants, including carbon monoxide and sulphur dioxide, the PSI measures. Long and regular exposure to PM2.5 is linked to higher risk of death from complications such as lung cancer or heart disease.

With the roll-out of bands and descriptors for one-hour PM2.5 readings, the three-hour PSI reading will be phased out by the year end.

Associate Professor Koh Tieh Yong, a weather scientist at SIM University, said the one-hour PM2.5 readings are a more "direct and sensitive measure" of fine-particulate pollution than the three-hour PSI. "The public should pay attention to the frequency and length of exposure as much as the PM2.5 descriptor bands," he added.

If both the one-hour PM2.5 readings and 24-hour PSI readings are in the high range, the public should refrain from going outdoors, said Professor Philip Eng, senior consultant respiratory physician at Mount Elizabeth Hospital. "But if there is a disconnect, then my advice is to take the worse of the two."

However, Dr Erik Velasco of the Singapore-MIT Alliance for Research and Technology said that having different air quality indicators can be confusing and the one-hour PM2.5 bandings do not provide any recommendations.

Ms Nicole Tan, 26, an early childhood educator who has two young children, said the bands are helpful. "The main thing I look out for in a reading is the PM2.5 concentration levels. That's usually my deciding factor when I want to take a trip out during haze periods," she said.