Haze in Singapore: PSI in unhealthy range for much of the island

SIGNAPORE – Singaporeans living in the west, central and east regions continued to experience an unhealthy level of pollutants in the air early on Oct 7.

The 24-hour Pollutant Standards Index (PSI) stood at 115 in the west, 129 in the central region and 118 in the east.

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.

PM2.5 readings, which are used as a gauge for immediate activities, were elevated in the same regions: 86 in the west, 68 in the central region and 56 in the east.

But the PSI for both the north (99) and south (97) regions remained at moderate levels, with the PM2.5 reading also remaining normal at 52 and 49 respectively.

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

At 6am on Oct 7, the PSI readings in the east, central and west regions had stood in the unhealthy range for over 24 hours, with levels in the north and south also dipping into this band for several hours before inching back into the moderate range.

In its daily haze advisory on Oct 6, the National Environment Agency said that with the prevailing winds expected to blow from the east-south-east to the south-east, the 24-hour PSI is forecast to be in the “high moderate to mid unhealthy” range.

Dry conditions are expected to persist over Kalimantan as well as central and southern Sumatra in neighbouring Indonesia, where moderate to dense smoke plumes were observed to be drifting towards Singapore.

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 – 164 in central Singapore – was recorded on Sept 29.

The developments in September mark 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 this year’s “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 and that the MSS, is expecting a transition only during late October or early November for Singapore, later than in the previous two years.

Daniel Lai is a journalist at the ST Now team, covering breaking news and international affairs.