At 10 pm on Saturday, the 24‑hour Pollutant Standards Index (PSI) in the central region reached 101, moving into the unhealthy band (101‑200). The east, west, south and north recorded 93, 90, 82 and 76 respectively.

The National Environment Agency (NEA) said moderate to dense smoke plumes from southern Sumatra and fires in Kalimantan were drifting toward Singapore, contributing to the haze.

The 24‑hour PSI is Singapore’s daily air‑quality indicator. It is calculated from six pollutants – PM2.5, PM10, ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide – and reflects the average conditions of the past 24 hours.

A 24‑hour PSI reading of 101‑200 is classified as “unhealthy”. The 1‑hour PM2.5 reading is considered elevated when it falls between 56 and 150 micrograms per cubic metre.

NEA advises healthy people to cut back on prolonged or strenuous outdoor activity when the 24‑hour PSI is unhealthy. Elderly people, pregnant women and children should minimise such activity, and anyone with chronic lung or heart disease should avoid it altogether.

For immediate plans, people should check the 1‑hour PM2.5 reading and follow the personal guide. For next‑day outings, they should look at the 24‑hour PSI forecast and the related health advisories.