NEA Explains Why 3-Hr PSI Reading Preferred

Despite calls for one-hour Pollutant Standards Index (PSI) readings during the haze crisis, the National Environment Agency (NEA) will not be providing it, citing a lack of support from health studies.

Ms Indrani Rajaram, project director and chief scientific officer of NEA’s pollution control department, reiterated that the public should use the three-hour PSI readings or the raw one-hour PM2.5 data – the dominant pollutant during periods of haze – to better plan their daily activities.  

As a gauge, the maximum concentration of PM2.5 on a regular, non-hazy day is usually between 20 micrograms and 35 micrograms per cubic metre. It becomes a serious problem when the numbers hit 100, and dangerous when it exceeds 200.

The NEA calculates PSI by inputting pollutant concentration data into a formula that takes into account the breakpoints - upper and lower concentration limits derived from health studies.

“If tomorrow there’s a health study, a very rigorous health study, that comes out and tells us one-hour PM2.5 concentration is harmful, we’ll use that to do a conversion (to get one-hour PSI). But at the moment the studies out there don’t give you a number that is supported by health studies to do this computing,” said Ms Indrani.

Source: “NEA: No to 1-hour PSI” (The Straits Times, 9 October 2015), “NEA explains why it does not give hourly PSI readings” (TODAYOnline, 9 October 2015) 

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