Air quality briefly returns to unhealthy range in central Singapore
The 24-hour PSI re-entered the unhealthy range in the central region at 9pm on Sunday and improved to the moderate range two hours later.
A view of the haze in Singapore on Oct 4, 2026. (Photo: CNA)
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SINGAPORE: Air quality in central Singapore briefly returned to the unhealthy range at 9pm on Sunday (Oct 4), while readings in the other four regions remained moderate.
At 9pm, the 24-hour Pollutant Standards Index (PSI) reading in the central region was 101.
At 11pm, the central region's reading dropped to 99, re-entering the moderate band. The readings in the other regions were 83 in the east, 86 in the west, 75 in the south and 79 in the north.
The 1-hour PM2.5 readings at 11pm, which reflect air quality at a single point in time, were in the elevated band in the west and in the normal range in the other four regions.
In an update earlier on Sunday, the National Environment Agency (NEA) said moderate to dense smoke plumes from southern Sumatra continued to drift towards Singapore and the surrounding region. Smoke haze was also observed from fires in Kalimantan.
Dry weather is expected to continue over Singapore and the surrounding region on Monday.
There remains a risk of smoke haze affecting Singapore under the prevailing southeasterly or southwesterly winds, NEA said.
The 24-hour PSI for Singapore is forecast to be in the high moderate to low unhealthy range, the agency added.
NEA said the health impact of haze depends on a person's health status, the PSI level, and the length and intensity of outdoor activity.
For immediate outdoor activities, people should refer to the 1-hour PM2.5 readings and corresponding personal guide, while the 24-hour PSI forecast and health advisories should be used when planning outdoor activities for the next day.
The 24-hour PSI is Singapore's indicator of daily air quality and forms the basis of NEA's daily health advisories. It is calculated using six air pollutants - PM2.5, PM10, ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide - and reflects the average air quality of the past 24 hours.
The 1-hour PM2.5 reading, on the other hand, is the hourly average of the PM2.5 pollutant levels. PM2.5 is fine particulate matter with a diameter of 2.5 micrometres or shorter, and is the dominant pollutant during haze that causes harm to health.
A 24-hour PSI reading is considered "unhealthy" when it is in the 101 to 200 range, "very unhealthy" when it is within the 201-300 range, and "hazardous" when it goes over 300.
The hourly PM2.5 reading is classified in four bands: normal, elevated, high and very high. It is considered elevated when it ranges from 56 to 150. The "high" band ranges from 151 to 250, and readings above that are classified as "very high".
