Singapore haze: PSI in unhealthy range across island

SINGAPORE – The air quality across Singapore remained in the unhealthy range early on Oct 8, with the 24-hour Pollutant Standards Index (PSI) at 7am standing at 113 in the north, 120 in the south, 127 in the east, 161 in the west and 146 in the central region.

Air quality is considered unhealthy when the PSI – a 24-hour rolling average of six key air pollutants and used in planning for outdoor activities the next day – is in the range of 101 to 200.

However, PM2.5 readings, which points to the current air quality and is used as a gauge for immediate activities, were elevated in only the west (80) at 7am.

They were in the normal band for the north (44), south (42), east (43) and central (53), though it was slightly elevated in the central region earlier at 6am.

An hourly PM2.5 reading between 56 and 150 indicates an elevated concentration of fine particles.

When the 24-hour PSI readings are in the unhealthy band, those who are healthy should reduce prolonged or strenuous outdoor physical activities, according to the National Environment Agency’s (NEA) haze advisory.

Vulnerable people – including the elderly, pregnant women, children and those with chronic lung or heart disease – should minimise or avoid such activities entirely.

In its daily haze advisory on Oct 7, the NEA had forecast that the haze situation would worsen, with the PSI expected to be in the unhealthy range.

It was the first time since the agency started issuing daily haze advisories on Sept 4 that the forecast has fallen completely within the unhealthy band of 101 and 200. Previous forecasts in the same period were in the moderate, or moderate to unhealthy ranges.

NEA said that moderate to dense smoke plumes from southern Sumatra in neighbouring Indonesia were observed to be drifting towards Singapore whilst there was also moderate to dense smoke haze from hotspots in Kalimantan.

“Under the prevailing south-easterly to southerly winds, smoke haze from these areas may continue to drift towards Singapore,” it added.

The PSI crossed into the unhealthy range four weeks ago, hitting 101 in central Singapore on the morning of Sept 4. In the days that followed, readings in the central, eastern and western parts of the island occasionally crossed into the unhealthy range.

The highest reading of the year – 167 in central Singapore – was recorded on Sept 29. That same day, the central region also saw the highest 1-hour PM2.5 reading of 2026 of 165 at midnight.

These developments over the past month marked the first time since October 2023 that the PSI in Singapore hit unhealthy levels because of haze, with the authorities earlier warning of the risk of haze between June and October as a result of warmer and drier conditions brought on by both El Nino and the Indian Ocean Dipole.

Some experts have predicted that the haze in Singapore in 2026 could last for a longer period due to the “Godzilla” El Nino event, which could reduce rainfall and result in higher temperatures over October-November, compared with non-El Nino years.

During non-El Nino years, the dry south-west monsoon season usually tapers off by September, and the start of the rainy north-east monsoon season tends to set in around late November.

The Meteorological Service Singapore (MSS) told The Straits Times that El Nino events, particularly strong ones, tend to delay the retreat of the dry season for much of the southern ASEAN region.

The Met service added that it is expecting a transition only during late October or early November for Singapore, later than in the previous two years.