SINGAPORE, Oct 7 — Unhealthy air persisted across large parts of Singapore early today, with pollution levels in the west, central and east remaining in the unhealthy range for more than 24 hours as smoke from Indonesia continued to drift towards the island.

At 6am, the 24-hour Pollutant Standards Index (PSI) stood at 129 in central Singapore, 118 in the east and 115 in the west, The Straits Times reported.

A PSI reading of between 101 and 200 is classified as unhealthy.

The north and south fared slightly better, with PSI readings of 99 and 97 respectively, putting them in the moderate range after both regions had briefly recorded unhealthy levels in the preceding hours.

Fine particulate matter was also elevated in the three worst-affected regions. Hourly PM2.5 readings stood at 86 in the west, 68 in central Singapore and 56 in the east.

Readings of between 56 and 150 indicate elevated concentrations of PM2.5, which are used by the authorities as a guide for immediate activities.

The National Environment Agency (NEA) said in its haze advisory yesterday that Singapore’s 24-hour PSI was expected to remain in the “high moderate to mid unhealthy” range as east-south-easterly to south-easterly winds prevailed.

Dry weather is expected to persist over Kalimantan and central and southern Sumatra, where moderate to dense smoke plumes have been observed drifting towards Singapore.

The latest episode extends a period of intermittent haze that began in early September.

Singapore’s PSI first crossed into the unhealthy range this season on September 4, when central Singapore recorded a reading of 101. Pollution levels in the central, eastern and western regions have since periodically breached the unhealthy threshold.

The highest PSI reading so far this year was 164 in central Singapore on September 29.

According to The Straits Times, September marked the first time since October 2023 that haze had pushed Singapore’s air quality into the unhealthy range.

Authorities had earlier warned of a heightened haze risk between June and October because of warmer and drier weather associated with El Niño and the Indian Ocean Dipole.

Some experts have said this year’s unusually strong El Niño — described as a “Godzilla” event — could prolong the haze season by suppressing rainfall and raising temperatures through October and November.

In years without El Niño, the dry south-west monsoon typically begins easing by September, before the wetter north-east monsoon sets in around late November.

The Meteorological Service Singapore told The Straits Times that strong El Niño events tend to delay the end of the dry season across much of the southern Asean region.

It expects Singapore’s transition away from dry conditions to occur only in late October or early November, later than in the previous two years.