Singapore air quality deteriorated on Sept 19, when the 24-hour Pollutant Standards Index in the central region crossed into the unhealthy range at 102 at 1pm and rose to 107 at 3pm, according to the National Environment Agency. Smoke plumes from forest fires in Kalimantan and southern Sumatra drifted toward the country amid dry conditions and prevailing east-south-east or south-east winds, marking the first time the PSI hit unhealthy levels due to haze since October 2023.
Central Region Air Quality Crosses Unhealthy Threshold
The 24-hour Pollutant Standards Index in central Singapore climbed from 102 at 1pm to 107 at 3pm on Sept 19, according to the National Environment Agency. Air quality is categorized as unhealthy when the 24-hour PSI ranges from 101 to 200, prompting the National Environment Agency to advise the public to reduce outdoor activities. Readings between 51 and 100 remain moderate, while values from zero to 50 stay good. The affected central region covers Thomson, Marymount, Sin Ming, Ang Mo Kio, Bishan, Serangoon Garden, MacRitchie, and Toa Payoh, based on the National Environment Agency website.
Conditions started worsening late on Sept 18. The PSI stood at 76 at 9pm before climbing overnight and crossing the 101 threshold by 1pm on Sept 19. Prior to this event, the PSI reached 101 in central Singapore on the morning of Sept 4. Readings in central, eastern, and western parts occasionally crossed into the unhealthy range in the days following that Sept 4 date.
Did You Know? September’s developments mark the first time since October 2023 that the PSI in Singapore hit unhealthy levels because of haze, with authorities previously warning of haze risks between June and October driven by warmer and drier conditions from both El Nino and the Indian Ocean Dipole.
Regional PSI Variations and PM2.5 Spikes
Readings outside the central region increased steadily throughout the day but stayed within the moderate range, according to the National Environment Agency. The west region recorded the next-highest PSI at 95 at 3pm, rising from 90 at 1pm. The south region registered the lowest PSI at 79 at 3pm, up from 75 at 1pm.
Hourly PM2.5 readings, which measure current fine particulate matter concentrations, spiked sharply in the central region at 11am on Sept 19, jumping from 67 to 117. Concentrations climbed further to 149 at noon before dropping to 93 at 3pm. PM2.5 levels are classified as elevated between 56 and 150, and high between 151 and 250. The National Environment Agency advises residents to check hourly PM2.5 readings for immediate activities and 24-hour PSI figures for daily planning.
According to agency guidance, tracking hourly PM2.5 concentrations helps individuals time immediate outdoor tasks safely, while the 24-hour PSI offers a reliable baseline for broader schedule adjustments during regional smoke events.
Sumatran and Kalimantan Smoke Plumes Drive Haze Risk
The National Environment Agency reported in its daily advisory on Sept 18 that smoke plumes from forest fires in Kalimantan were observed drifting toward Singapore, alongside plumes spotted in southern Sumatra. Dry conditions are forecast to persist over parts of southern Sumatra and Kalimantan. Prevailing winds blowing from the east-south-east or south-east could carry additional smoke haze toward Singapore. The agency forecast the 24-hour PSI to remain in the high moderate to low unhealthy range.
Frequently Asked Questions
What is the unhealthy range for the 24-hour PSI?
The 24-hour Pollutant Standards Index is considered unhealthy when readings fall between 101 and 200, according to the National Environment Agency.
Which areas are included in Singapore’s central region?
The central region covers Thomson, Marymount, Sin Ming, Ang Mo Kio, Bishan, Serangoon Garden, MacRitchie, and Toa Payoh, according to the National Environment Agency website.
What caused the haze conditions in September?
Smoke plumes from forest fires in Kalimantan and southern Sumatra drifted toward Singapore amid dry conditions driven by El Nino and the Indian Ocean Dipole, according to the National Environment Agency.
How are you adjusting your daily routines while the regional haze persists?
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