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

On September 19, the air quality in Singapore deteriorated as the 24-hour Pollutant Standards Index (PSI) in the central region crossed back into the unhealthy range. The PSI reading reached 102 at 1pm. Air quality is deemed unhealthy when the 24-hour PSI falls between 101 and 200, during which the National Environment Agency (NEA) advises the public to limit outdoor activities. PSI readings between 51 and 100 are considered moderate, while values ranging from 0 to 50 are classified as "good."

Hourly PM2.5 readings, which measure the current concentrations of fine particulate matter, surged in the central region at 11am on September 19, rising from 67 to 117. The PM2.5 readings remained elevated, between 56 and 150, before falling to 141 at 1pm. The NEA recommends referring to the hourly PM2.5 reading for immediate activities and the 24-hour PSI for daily planning.

The central region, which includes Thomson, Marymount, Sin Ming, Ang Mo Kio, Bishan, Serangoon Gardens, MacRitchie, and Toa Payoh, experienced deteriorating air quality late on September 18. The PSI reading was 76 at 9pm, and it continued to rise overnight, crossing the 101 threshold at 1pm on September 19.

Smoke plumes from forest fires in Kalimantan were observed drifting towards Singapore on September 18, with some smoke plumes also seen in southern Sumatra. Dry conditions are expected to persist over parts of southern Sumatra and Kalimantan, potentially causing smoke haze to affect Singapore as prevailing winds are forecast to blow from the east-southeast or south-east. The 24-hour PSI is projected to remain in the high moderate to low unhealthy range.

This marks the first time since October 2023 that Singapore has experienced unhealthy air quality levels due to haze. Authorities had previously warned of the risk of haze between June and October, due to warmer and drier conditions caused by both El Nino and the Indian Ocean Dipole.