The 24-hour PSI in western Singapore rose to 161 at 6am on Thursday, 8 October, the highest of the five regions, as the National Environment Agency (NEA) kept its 24-hour PSI forecast in the unhealthy range heading into the Formula 1 weekend. All five regions were above 100, from the north at 113 to the west at 161.
At 6pm on Wednesday, the range was 105 to 140. Since then, the 24-hour PSI has climbed in the west, central, north and south regions, while the 1-hour PM2.5 readings that NEA uses for decisions about the next hour moved the other way overnight.
Two readings, two questions
NEA publishes two numbers, and it uses them for different decisions. The 24-hour PSI is an average of pollutant levels over the past 24 hours. NEA’s advice is to use the 24-hour PSI forecast to plan outdoor activities for the next day. The 1-hour PM2.5 concentration covers only the latest hour, and NEA’s personal guide uses it for decisions about going out now.
The gap between the two showed overnight. At 6am, the 1-hour PM2.5 readings were 61 µg/m³ in the central region, 76 in the west, 40 in the north, 44 in the south and 41 in the east. That put the north, south and east back in Band 1, Normal, while the central and west were still in Band 2, Elevated.
The 24-hour PSI did not follow, because it still carried Wednesday afternoon’s smoke. At 4pm on Wednesday, the 1-hour PM2.5 reading in the west reached 152 µg/m³, in Band 3, High. NEA says the 1-hour figure can be volatile and tends to swing over the day in transboundary haze.
The forecast into the weekend
NEA’s forecast for Singapore’s 24-hour PSI is in the unhealthy range. In its update on Wednesday evening, NEA said moderate to dense smoke plumes from southern Sumatra had drifted towards Singapore, and smoke haze from hotspots in Kalimantan had also been observed.
Dry conditions are expected to continue over central and southern Sumatra and many parts of Kalimantan. Under southeasterly to southerly winds, smoke from those areas may keep drifting towards Singapore. NEA’s outlook for the next few days is for dry weather over most of the southern ASEAN region, with the hotspot and haze situation likely to stay escalated and a continued risk of transboundary haze.
What NEA advises at each level
For next-day plans, the advice follows the 24-hour PSI band:
- Moderate (51 to 100): normal activities for everyone.
- Unhealthy (101 to 200): healthy people should reduce prolonged or strenuous outdoor exertion; the elderly, pregnant women and children should minimise it; people with chronic lung or heart disease should avoid it.
- Very unhealthy (201 to 300): healthy people should avoid prolonged or strenuous outdoor exertion; the elderly, pregnant women and children should minimise outdoor activity; people with chronic lung or heart disease should avoid outdoor activity.
For the next hour, the advice follows the 1-hour PM2.5 band. At Band 1, Normal (0 to 55 µg/m³), activities carry on as usual. At Band 2, Elevated (56 to 150), healthy people should reduce strenuous outdoor activity and vulnerable groups should avoid it. At Band 3, High (151 to 250), healthy people should avoid strenuous outdoor activity and vulnerable groups should avoid all outdoor activity.
Schools take their own measures at each PSI level, which we explain in our MOE haze guide.
Race nights in the open air
NEA says the health impact of haze depends on a person’s health, the PSI level, and how long and how hard someone is active outdoors.
The Singapore Grand Prix runs on the Marina Bay Street Circuit from Friday to Sunday, 9 to 11 October, with sessions into the night on all three days. Under NEA’s guide, a spectator would use Thursday evening’s 24-hour PSI forecast to plan Friday, then check the 1-hour PM2.5 band on haze.gov.sg or the myENV app before heading out.
