Haze in Singapore: PSI readings reach unhealthy levels

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 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 reading for all regions remain in the normal range as at 1pm on Sept 20.

In the central region, PM2.5 reading crept downwards after hitting a daily high of 149 at 12pm on Sept 19.

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.

The 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 19, the NEA said the 24-hour PSI forecast is set to be within the “high moderate to mid unhealthy” range, even following afternoon showers over the central and western parts of Singapore.

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 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 the island 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.