Haze in Singapore: PSI may reach ‘very unhealthy’ range, says NEA

What is the Pollutant Standards Index (PSI), and what does an “unhealthy to low very unhealthy” reading mean?

The Pollutant Standards Index, or PSI, is a number used to describe overall air quality. It combines readings for major pollutants and presents them on a common scale. Singapore generally classifies 0–50 as good, 51–100 as moderate, 101–200 as unhealthy, and 201–300 as very unhealthy. These bands show why the NEA forecast mattered: pollution was expected to affect health, not merely reduce visibility.

On Oct 9, the NEA said Singapore’s 24-hour PSI could reach the “unhealthy to low very unhealthy range” on Oct 10. A reading of 135 is unhealthy. A reading of 192 is also unhealthy, but close to the very unhealthy threshold. The central reading was therefore especially concerning.

At 6pm, readings ranged from 135 in the north to 192 centrally. The central figure was Singapore’s highest since haze returned in September. Showers might help, but drifting smoke and dry conditions could keep the PSI elevated.

How severe are PSI readings of 135 in northern Singapore and 192 in central Singapore compared with normal conditions and recent haze levels?

PSI readings of 135 and 192 indicate substantially degraded air compared with normal conditions. On Singapore’s scale, 0–50 is generally considered good, while 101–200 is unhealthy. That places both readings firmly in the unhealthy band. The higher the number, the greater the concern about exposure to pollution over the measured period.

The difference across Singapore was also notable. At 6pm, the north recorded 135, while central Singapore recorded 192. The central reading was 57 points higher and close to the 201 threshold for very unhealthy air. This shows that haze levels were not identical across the island.

The 192 reading was unchanged from 5pm and was the highest recorded since haze returned in September. The NEA forecast that the 24-hour PSI could reach the unhealthy to low very unhealthy range on Oct 10. Weather and incoming smoke would shape what happened next.

What health effects can people experience when haze and fine particles reach these levels?

Haze contains airborne particles and gases that can irritate the body. At unhealthy PSI levels, people may notice sore or dry eyes, a scratchy throat, coughing, phlegm, wheezing, or shortness of breath. These effects matter because polluted air can make breathing harder and reduce comfort during ordinary activities.

Fine particles are especially concerning because they can travel deep into the lungs. Exposure may worsen asthma, chronic lung disease, or other existing respiratory problems. People with heart or lung conditions, children, older adults, and those exercising outdoors are generally more vulnerable. Healthy people can also experience symptoms when pollution is high.

The article does not list specific health symptoms, but it reports readings of 135 to 192 and a forecast reaching the unhealthy to low very unhealthy range. During such conditions, reducing outdoor exposure and following official health guidance can limit risk. The actual effect depends on concentration, duration, and individual health.

What is PM2.5, and why is it an important part of measuring the danger from haze?

PM2.5 refers to fine particulate matter with diameters of 2.5 micrometres or less. These particles are much smaller than visible dust. Because they remain suspended in air and can be inhaled deeply, they provide an important measure of pollution that people may breathe during haze episodes.

The article reports PM2.5 readings from 80 to 123 at 6pm. Those readings add detail to the PSI, which summarizes air quality using several pollutant measures. A PSI number describes the broader pollution situation, while PM2.5 focuses specifically on fine particles. Together, they show both overall conditions and one especially important hazard.

The article does not state the health threshold for each PM2.5 value, but the reported range indicates substantial fine-particle pollution alongside PSI readings of 135 to 192. As haze drifts in, monitoring PM2.5 helps authorities track changes and helps people understand why outdoor exposure may be harmful.

How can smoke from fires in Sumatra and Kalimantan travel across the sea to Singapore?

Smoke haze does not need to remain near its source. Once smoke enters the atmosphere, regional winds can carry it over large distances. Singapore lies near Sumatra and Kalimantan, so wind direction strongly affects whether pollution moves toward the island. This is why haze can arrive even when the fires are elsewhere.

The NEA observed moderate to dense smoke haze from southern and central Sumatra drifting towards Singapore. It also reported smoke haze in parts of Kalimantan. Under prevailing southeasterly or southwesterly winds, airborne smoke was carried across the surrounding sea and into Singapore’s air.

The transport can continue while the source regions remain smoky and the winds keep blowing toward Singapore. On Oct 9, readings reached 192 in central Singapore, the highest since haze returned in September. The forecast warned that incoming haze could persist despite some showers, because dry conditions were expected in parts of southern Sumatra and Kalimantan.

How might showers over Singapore and nearby areas reduce haze, and why could dry weather in Indonesia allow it to continue?

Showers can reduce haze in two ways. Falling raindrops capture some particles in the air, and rain can clear the atmosphere temporarily. Wet conditions may also suppress smoke near its source. The result can be cleaner air, although the benefit depends on how widespread and persistent the rain is.

The NEA forecast some showers over Singapore and parts of the surrounding region over the weekend. That offered a possible short-term improvement. However, rain in Singapore alone would not remove smoke continuously if polluted air kept arriving from elsewhere. Weather conditions across the whole region therefore mattered.

Dry conditions were expected to continue over parts of southern Sumatra and parts of Kalimantan. Those conditions could allow smoke haze to persist or continue forming, while prevailing southeasterly or southwesterly winds pushed it towards Singapore. The NEA therefore warned that showers might not prevent further haze, and the PSI could still reach the unhealthy to low very unhealthy range.

Why do fires in tropical forests and peatlands produce so much long-lasting smoke, and how do winds and the atmosphere carry that pollution?

The source article does not explain how forest or peatland fires behave, but established atmospheric science provides the mechanism. Tropical vegetation supplies abundant organic fuel. Peat is partly decomposed plant material stored in wet ground. When it dries and burns, it can smoulder below the surface rather than disappearing quickly. That produces persistent smoke, sometimes even when flames are not obvious.

Smoke contains fine particles and gases released by incomplete burning. Winds can lift and carry this pollution across regions and over the sea. The direction and strength of those winds determine whether smoke moves towards Singapore. Atmospheric mixing also affects how widely pollution spreads and how concentrated it remains near the surface.

In this episode, the NEA observed moderate to dense haze from southern and central Sumatra, plus haze in parts of Kalimantan. Prevailing southeasterly or southwesterly winds carried it towards Singapore. Dry conditions could prolong the sources, while showers might temporarily clear some pollution.

Key Facts:

📌 The PSI summarizes air pollution using a common numerical scale.

📌 Singapore’s 24-hour PSI was forecast to reach unhealthy levels.

📌 Central Singapore recorded a PSI of 192 at 6pm.

📌 Northern Singapore recorded a PSI of 135 at 6pm.

📌 Central Singapore recorded a PSI of 192 at 6pm.

📌 The central reading was highest since haze returned in September.

📌 Unhealthy haze can cause coughing, eye irritation, and breathing discomfort.