Air quality in central and southern Singapore deteriorated into the Unhealthy range on Monday evening as smoke haze from fires in southern Sumatra and Kalimantan drifted across the island.
At 8pm on Sept. 28, Singapore’s 24-hour Pollutant Standards Index (PSI) ranged from 73 to 104, placing readings across the island in the Moderate to Unhealthy range. Southern Singapore recorded a PSI of 103, while the central region reached 104, the highest readings among the five regions.
One-hour PM2.5 concentrations were also in the Elevated band across all five regions. Central Singapore recorded the highest one-hour PM2.5 reading at 149 micrograms per cubic metre, just below the High band, which begins at 151.
The deterioration followed earlier signs that haze conditions were worsening during the day. At 6pm, the 24-hour PSI had ranged from 68 to 94, with southern Singapore recording the highest reading. One-hour PM2.5 concentrations were between 64 and 138 micrograms per cubic metre.
The smoke originated from fires in southern Sumatra and Kalimantan, with moderate to dense haze drifting toward Singapore. Dry conditions are expected to persist in parts of those areas, while prevailing winds from the east or southeast could continue carrying smoke toward the island.
Authorities are forecasting that Singapore’s 24-hour PSI could reach the high-Moderate to mid-Unhealthy range, meaning haze conditions could remain variable and potentially worsen in some areas.
The latest readings have also renewed attention on the difference between the 24-hour PSI and one-hour PM2.5 readings. The PSI is used to assess broader air-quality conditions and plan activities for the following day, while one-hour PM2.5 readings provide a more immediate indication of conditions for people planning to spend time outdoors.
Health guidance varies according to the severity of the haze and an individual’s health status. During Unhealthy PSI conditions, healthy people are advised to reduce prolonged or strenuous outdoor physical activity, while elderly people, children and pregnant women are advised to minimise such activities. People with chronic heart or lung conditions are advised to avoid prolonged or strenuous outdoor exertion.
The haze episode is being driven by regional fires rather than pollution generated solely within Singapore. Weather conditions, wind direction and rainfall will therefore play an important role in determining how much smoke reaches the island and how quickly conditions improve.
For now, the return of Unhealthy readings in central and southern Singapore shows that the haze situation remains changeable, with air quality capable of deteriorating again even after earlier readings remained within the Moderate range.
As dry conditions persist in parts of Indonesia and winds continue to favour the movement of smoke toward Singapore, residents are being urged to monitor both the latest PSI and one-hour PM2.5 readings before planning outdoor activities.
