Haze in S’pore: Air quality returns to moderate levels in all regions

SINGAPORE – The 24-hour Pollutant Standards Index (PSI) readings across all regions returned to moderate levels as at 11pm on Sept 30.

This comes after the central region reached a new peak this haze season early on Sept 29, when air quality across Singapore breached the unhealthy band for the first time in two weeks.

As at 11pm on Sept 30, the PSI reading for the central region was 99, while the values for the other regions ranged from 81 to 99. This is down from a peak of 134 in the central and western regions earlier in the day at 1am.

The PSI reading is a 24-hour rolling average of six key air pollutants and is used in planning for outdoor activities the next day.

Air quality is considered unhealthy when the 24-hour PSI is in the range of 101 to 200, during which the National Environment Agency (NEA) advises the public to at least reduce outdoor activities. PSI readings of 51 to 100 are considered moderate, while values of zero to 50 are in the “good” range.

Early on Sept 29, the PSI value in the central region reached a new peak this haze season, standing at 164 at 10am, surpassing the previous high of 154 on Sept 15.

Also on Sept 29, the readings in all five regions here surpassed the 101 threshold into the unhealthy range. The last time that happened was also Sept 15.

The hourly PM2.5 readings for all regions are all in the normal band as of 11pm on Sept 30, with the values ranging between 18 and 37.

PM2.5 readings, which indicate the current concentrations of fine particulate matter, are considered elevated if they fall between 56 and 150, and high if they are between 151 and 250.

NEA has advised the public to refer to the hourly PM2.5 reading if they are considering immediate activities and the 24-hour PSI readings to plan for the day ahead.

In its daily haze advisory on Sept 30, NEA said the 24-hour PSI is forecast to be in the “moderate to low unhealthy” range, following an improvement in the haze situation with showers over Singapore and the surrounding region.

Dry conditions are forecast to continue over parts of southern Sumatra and south-western Kalimantan. While showers are expected over Singapore and the surrounding region again on Oct 1, the risk of smoke haze affecting the Republic remains as the prevailing winds are expected to blow from the south-east or south.

The PSI crossed into the unhealthy range around 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 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.

Dilenjit Singh is a correspondent at The Straits Times’ breaking news desk.