24-hour PSI rises to 177 in central region, highest in this haze season

SINGAPORE: Air quality in Singapore worsened on Friday (Oct 9) morning, with the 24-hour Pollutant Standards Index (PSI) in the central region rising to 177 at 11am, the highest for this year's haze season. 

The 24-hour PSI had been rising steadily across regions from midnight, and all regions were in the unhealthy range. At 11am, the readings were 119 in the north, 168 in the west, 157 in the south and 151 in the east.

The 1-hour PM2.5 crossed into the high band in the central region at 11 am, reaching 152.

Other regions across Singapore remained in the elevated band, with readings ranging from 96 to 116.

In its latest haze situation update on Friday morning, the National Environment Agency (NEA) said moderate to dense transboundary smoke haze was covering parts of Peninsular Malaysia, Singapore, Kalimantan and the southern and central parts of Sumatra.

"Many air quality stations in Peninsular Malaysia, Singapore, Kalimantan and Sumatra are reporting unhealthy to hazardous levels," NEA said.

Isolated to scattered hotspots were detected in Kalimantan and the southern and central parts of Sumatra, while few hotspots were detected elsewhere in the southern Association of Southeast Asian Nations (ASEAN) region, the agency said.

But it noted that the hotspot situation in Kalimantan and parts of Sumatra could not be fully determined due to obscuration by thick smoke haze and cloud cover.

The smoke haze situation over parts of the region also could not be fully determined due to cloud cover, NEA added.

Dry conditions are expected to continue over parts of the southern ASEAN region, apart from Peninsular Malaysia, Sumatra and the northern and central parts of Borneo, where showers are expected.

"While the hotspot and smoke haze situation may improve in areas experiencing showers, the situation is expected to stay elevated in fire-prone regions experiencing prolonged dry conditions, with a continued risk of severe transboundary haze occurrence," said NEA.

For those planning immediate outdoor activities, NEA advises checking the hourly PM2.5 levels.

The 24-hour PSI forecast and corresponding health advisories should be used in planning next day outdoor activities.

When 1-hour PM2.5 levels are elevated, healthy people are advised to reduce strenuous outdoor activity for the next hour, while the elderly, pregnant women, children and people with chronic heart or lung conditions should avoid such activity.

The 24-hour PSI is Singapore's indicator of daily air quality and forms the basis of NEA's daily health advisories. It is calculated using six air pollutants - PM2.5, PM10, ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide - and reflects the average air quality of the past 24 hours.

The 1-hour PM2.5 reading, on the other hand, is the hourly average of the PM2.5 pollutant levels. PM2.5 is fine particulate matter with a diameter of 2.5 micrometres or shorter, and is the dominant pollutant during haze that causes harm to health.

A 24-hour PSI reading is considered "unhealthy" when it is in the 101 to 200 range, "very unhealthy" when it is within the 201-300 range and "hazardous" when it goes over 300.

The hourly PM2.5 reading is classified in four bands: normal, elevated, high and very high. It is considered elevated when it ranges from 56 to 150. The "high" band ranges from 151 to 250, and readings above that are classified as "very high".

In its Thursday evening advisory, the National Environment Agency (NEA) said that moderate to dense smoke plumes from southern and central Sumatra and West Kalimantan were observed to drift towards Singapore.

Dry conditions are expected to persist over the southern parts of Sumatra and parts of Kalimantan.

Under prevailing southeasterly or southerly winds, smoke haze may continue to drift towards Singapore, NEA said, adding that the 24-hour PSI for Singapore is forecast to be in the high moderate to mid unhealthy range.