Air quality in western Singapore moved into the unhealthy range on Friday (Oct 23), with hourly PM2.5 readings climbing across all five regions of the island, according to CNA.
The 24-hour Pollutant Standards Index (PSI) for the west reached 103 at 4pm, placing it inside the unhealthy band of 101 to 200. The other four regions stayed within the good to moderate range, and islandwide PSI readings spanned 79 to 103, CNA reported.
Hourly PM2.5 readings were elevated everywhere, ranging from 69 to 124 at 4pm. The west was the first region to show raised PM2.5 levels, at 10am, followed by the central and southern regions at 11am, the east at noon and the north at 1pm.
The decline came one day after conditions had eased. On Thursday, air quality across Singapore returned to the good to moderate range, and the west's PSI dropped out of the unhealthy band at 3pm.
Why it matters
The reading marks a reversal after a brief improvement, and it affects how people across the island plan their day outdoors. When the 24-hour PSI sits in the unhealthy range, the National Environment Agency (NEA) advises the elderly, pregnant women and children to cut back on long or strenuous outdoor physical activity. People with chronic conditions, including heart or lung disease, are told to avoid such exertion altogether.
NEA had signalled the shift in advance. On Thursday evening, the agency forecast that Singapore's PSI could land between 101 and 150 on Friday, according to CNA.
Regional hotspots and drifting smoke
In a Friday morning warning, NEA said the danger of severe transboundary haze had not passed. The agency reported widespread hotspots in southern Kalimantan and Sumatra, CNA reported.
Moderate to dense smoke haze was seen over parts of Kalimantan, Singapore, southern Peninsular Malaysia, southern and central Sumatra, and western Sarawak.
NEA said rain could bring some relief, but the broader hotspot and smoke situation was likely to stay elevated, particularly in areas under prolonged dry conditions. The agency maintained that the risk of severe transboundary haze occurring again remains.
On wind patterns, NEA said air over the southern ASEAN region is expected to move mainly from the southeast to the southwest. Over Peninsular Malaysia and northern Sumatra, winds are likely to come from the west to northwest.
Separate reporting pointed to a similar outlook. AsiaOne reported that smoke haze could affect Singapore until Saturday, with conditions expected to improve on Sunday, citing NEA.
Reading the numbers and choosing protection
The 24-hour PSI and the one-hour PM2.5 figures serve different purposes, and NEA directs the public to the hourly PM2.5 readings when deciding on masks and immediate outdoor plans.
Under Ministry of Health (MOH) guidance, when one-hour PM2.5 readings fall in the high band, vulnerable groups — the elderly, pregnant women and people with chronic heart or lung conditions — should stay away from outdoor activity. Anyone who must go outside for short errands may wear a well-fitting N95 mask or an equivalent to lower exposure to haze particles.
If one-hour PM2.5 readings climb to the very high band of 251 and above, healthy people should also keep outdoor activity to a minimum, and those who need to go out can likewise use an N95 mask.
MOH said N95 masks are generally unnecessary for trips between home and school or work, or while indoors. The ministry also advised the elderly, pregnant women and people with severe heart or lung conditions who have trouble breathing to check with a doctor before wearing an N95 mask, and to take a break if a mask causes discomfort.
Other mask types can help as well. According to MOH, KN95, FFP2 and KF94 masks are also effective at reducing exposure to haze particles. The public can check the HazeMaskGoWhere website for collection points and live updates on stock at vending machines.
MOH issued guidance on Oct 13 covering which masks offer protection against haze. Surgical masks, the ministry said, can ease discomfort and lower infection risk by blocking larger irritant particles. But when PM2.5 readings exceed 250 and people expect to be outdoors for several hours, MOH recommends an N95 or equivalent. Cloth masks generally do not filter fine particles well, though they can block larger irritants and reduce discomfort.
The wider policy picture has drawn attention too. The South China Morning Post reported on Singapore's tougher stance against haze under the framing "as long as it takes," while questioning whether the approach will succeed.
For now, residents should watch the hourly PM2.5 readings and NEA's daily forecasts, with Sunday flagged as the earliest likely improvement.
