Singapore started the week with improved air quality, with the 24-hour Pollutant Standards Index (PSI) remaining in the moderate range across all five regions on Sept. 21.
At 10am, PSI readings ranged from 68 to 86, while one-hour PM2.5 concentrations stood between 26 and 41 micrograms per cubic metre, remaining within the normal band. The improvement followed a period of worsening haze that had pushed parts of Singapore into the unhealthy range over the weekend.
The central region, which had recorded unhealthy air quality from Sept. 19, returned to the moderate range at 7pm on Sept. 20. By Monday evening, the 24-hour PSI across Singapore was between 66 and 81, while one-hour PM2.5 readings remained in the normal band.
However, the improvement does not mean the haze threat has disappeared.
Singapore’s National Environment Agency said moderate to dense smoke plumes continued to be detected from fires in Kalimantan and southern Sumatra. Dry conditions were also expected to persist in parts of southeastern Sumatra and southwestern Kalimantan.
With prevailing winds continuing to blow from the southeast, smoke haze could still affect Singapore. The 24-hour PSI forecast was therefore placed in the moderate to low-unhealthy range.
Rain provided some relief on Sept. 21, with showers falling over many parts of Singapore during the afternoon. The weather helped keep particulate pollution at relatively lower levels, although haze conditions remain dependent on wind direction, rainfall and the intensity of fires across the region.
Singapore’s air quality has fluctuated considerably in recent weeks. PSI readings in the central region crossed into the unhealthy range on Sept. 19 before improving the following day, while other regions also briefly recorded unhealthy readings during the period.
Under Singapore’s air-quality guidelines, a 24-hour PSI reading of 51 to 100 is considered moderate, while 101 to 200 is classified as unhealthy. The NEA advises people to use one-hour PM2.5 readings when deciding on immediate outdoor activities and the 24-hour PSI forecast when planning activities for the following day.
For now, Singapore’s air has improved, but conditions remain closely tied to the fires and weather across Sumatra and Kalimantan. If dry weather and southeasterly winds persist, the haze could return — leaving the bigger question of whether the latest improvement will last.
