Air quality to be in mid-to-high end of moderate range: NEA

SINGAPORE — After a weekend that saw the Pollutant Standards Index (PSI) creeping into unhealthy levels, air quality is expected to be in the mid-to-high end of the moderate range today, the National Environment Agency (NEA) said last evening.

And in response to complaints by members of the public that the PSI readings on Sunday did not correspond to the visibly worsening air quality in many parts of Singapore, the agency said pollutant concentrations may be volatile from one hour to the next.

As of 8pm yesterday, the 24-hour PSI reading was 76 to 85, within the high end of the moderate range.

The total number of hot spots detected yesterday in Indonesia’s Sumatra and Kalimantan — which caused the haze experienced in Singapore — was 78 and 107 respectively, mostly in the southern parts of the islands. Smoke plumes and haze were visible in the vicinity of some hot spots in Sumatra.

Prevailing winds are forecast to blow mainly from the south-east today. While people can continue with their normal activities today, those who are not feeling well, especially the elderly, children and people with chronic heart or lung conditions should seek medical attention, the NEA said.

Earlier on Sunday evening, many TODAY readers had complained about worsening air quality in many areas of Singapore and a strong odour in the air — even though the PSI was still in the “moderate” range. The PSI reading caught up only on Sunday night, hitting a high of 129 at 9pm.

The complaints about PSI readings came despite the introduction of a new air quality reporting system in April, which is supposed to better reflect visibility levels during haze as it incorporates levels of fine particulate matter, PM2.5, into the PSI. Then, an NEA spokesperson had said the new system would pass the “window test” and “correspond more closely with what one sees”.

In response to TODAY’s queries, the NEA said yesterday: “The three-hour PSI at any time is based on PM2.5 concentration levels averaged over the previous three hours. As the hour to hour concentrations may be very volatile during a haze episode with short periods of transiently high PM2.5 levels, which can improve rapidly in the subsequent one to two hours, the three-hour PSI may not correspond to what one observes at that specific instant.”

It added that since April, the NEA has also made available one-hour PM 2.5 concentration levels on the NEA website, the haze microsite and myENV app. “Members of the public can make use of the three-hour PSI or one-hour PM2.5 concentration levels as a guide to adjust their immediate activities, like going for a jog outside,” the agency said.

A PSI reading of 101 to 200 falls within the unhealthy range, while a 51 to 100 reading is considered moderate.