Hazy conditions in Singapore may ease on Oct 9

SINGAPORE – The haze situation here on Oct 9 may ease slightly, with the National Environment Agency (NEA) forecasting that the 24-hour Pollutant Standards Index (PSI) readings will be in the high moderate to mid-unhealthy range.

This is compared with the agency’s haze advisory a day earlier, when it forecast the PSI readings on Oct 8 to be entirely in the unhealthy band.

The 24-hour PSI reading is a 24-hour rolling average of six key air pollutants, including fine particulate matter (PM2.5). PM2.5 is the dominant pollutant during periods of transboundary haze, and has the most influence over the 24-hour PSI readings.

On average, PM2.5 readings across all five regions on Oct 8 were lower than that on Oct 7, with the NEA saying that there were brief showers in the north of Singapore on Oct 8.

However, readings in some areas here climbed to the high band on the night of Oct 8.

A reading of 158 was recorded at 10pm in the western part of Singapore before dropping slightly to 156 at 11pm, but remaining in the high range.

In the central area, the reading hit the high threshold of 151 at 9pm, then dropped to the elevated band with a value of 139 an hour later before spiking to 163 at 11pm.

The PM2.5 reading in the east also entered the high band at 11pm, with a value of 152. The PM2.5 values for the north (83) and south (142) remained in the elevated range as at 11pm.

An hourly PM2.5 reading from 56 to 150 indicates elevated pollution levels, while values of 151 to 250 represent high pollution levels.

Meanwhile, the 24-hour PSI readings were in the unhealthy band across Singapore from noon on Oct 7 to 5pm on Oct 8.

The reading for the northern part of Singapore dropped to 100 at 6pm the same day, before dipping further to 99 at 11pm. However, the PSI readings remained in the unhealthy band for the rest of Singapore, ranging from 109 in the south to 142 in the west at 11pm.

Air quality is considered unhealthy when the PSI reading ranges from 101 to 200, during which the NEA advises the public to at least reduce prolonged or strenuous outdoor activities. PSI readings of 51 to 100 are considered moderate, while values of zero to 50 are in the “good” range.

Oct 7 was the first time, since the NEA 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.

In its Oct 8 advisory, NEA said moderate to dense smoke plumes from southern and central Sumatra and West Kalimantan were observed to be drifting towards Singapore, with dry conditions expected to continue in the neighbouring Indonesian territories.

“Under the prevailing south-easterly or southerly winds, smoke haze 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 and 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.