Haze in Singapore: PSI in central region back in the unhealthy range

SINGAPORE – The air quality in Singapore deteriorated on Sept 19 with the 24-hour Pollutant Standards Index (PSI) in the central region crossing into the unhealthy region again.

The 24-hour PSI reading in the area was 102 at

1pm.

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

The hourly PM2.5 readings, which indicate the current concentrations of fine particulate matter, skyrocketed in the central region at 11am on Sept 19, moving from 67 to 117.

It increased further to 149 at noon, before falling to 141 at 1pm.

PM2.5 readings are considered elevated if they fall between 56 and 150, and high if they are between 151 and 250.

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

The central region includes the Thomson, Marymount, Sin Ming, Ang Mo Kio, Bishan, Serangoon Gardens, MacRitchie and Toa Payoh areas, according to the NEA website.

The air quality had begun deteriorating late on Sept 18, with the PSI reading at 76 at 9pm before creeping up again overnight and crossing the 101 threshold at 1pm on Sept 19.

In its daily advisory on Sept 18, the NEA said smoke plumes from forest fires in Kalimantan were observed to be drifting towards Singapore. Some smoke plumes were also observed in southern Sumatra.

Dry conditions are forecast to continue over parts of southern Sumatra and Kalimantan and smoke haze might affect Singapore as the prevailing winds are expected to blow from the east-south-east or south-east.

The 24-hr PSI was forecast to be in the high moderate to low unhealthy range, added the NEA.

The PSI crossed into the unhealthy range two 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 Singapore occasionally crossed into the unhealthy range.

September’s developments 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.