The PSI first entered the unhealthy range late on Wednesday, reaching 102 at 11 p.m. It then rose to 104 at 6 a.m. and 106 at 9 a.m. on Thursday, while other regions stayed in the moderate range.

The National Environment Agency (NEA) said the haze comes from moderate to dense smoke plumes from fires in southern and central Sumatra and in Kalimantan. Some of this smoke drifted toward Singapore.

The unhealthy PSI band is 101‑200. A reading of 201‑300 is called “very unhealthy”, and any value above 300 is “hazardous”.

Air quality first fell into the unhealthy range since 2023 on 4 September, when the central PSI peaked at 123. The high reading led the NEA to start daily haze advisories from the evening of 4 September.