Why does Singapore’s PSI readings differ from the air quality index found on other websites? NEA explains: https://str.sg/7yYH
Experts also said that the country’s central region registers the worst air quality due to high urbanisation.
Here's the full detailed account:
🌫️ Central Singapore: Worst Air Quality — Why?
📊 The Situation (Sep 2026)
- Haze since Sep 4; central region consistently highest PSI across all 5 zones
- Sep 15, 6am: Central hit 154 (unhealthy); others 104–128 — first time since 2019 all regions unhealthy
- 11:30pm Sep 15: Central 115; West 101; East 95; North 86; South 82
- Central covers: Thomson, Marymount, Sin Ming, Ang Mo Kio, Bishan, Serangoon Gardens, MacRitchie, Toa Payoh
🧑🔬 Expert Explanations
Urban heat & turbulence — NUS Adj. Assoc. Prof. Koh Tieh Yong:
- Central = most built-up & urbanised → concrete retains heat → stronger updrafts & air turbulence
- Incoming PM2.5 from Indonesia fires gets trapped & concentrated closer to ground by this turbulent air
- When haze is thick enough, entire island becomes unhealthy (as seen Sep 15)
Dry conditions + local emissions — NTU Prof. Steve Yim:
- Dry weather allows haze particles from Indonesia to mix with downtown/local emissions, amplifying central readings
⚖️ PSI vs Other AQI — NEA's Clarification
Key Differences
Singapore 24-hr PSI Other AQI (e.g. aqicn.org, IQAir)
Calculation Based on 24-hour averages for all 6 pollutants[__LINK_ICON] Uses shorter averaging periods (1-hr) & different formulas
Pollutants PM2.5, PM10, SO₂, NO₂, O₃, CO — all measured by highly specialised, certified equipment[__LINK_ICON] May use NEA data + low-cost, less consistent sensors from private contributors[__LINK_ICON]
Result Generally lower/milder readings than AQI Often higher/poorer air quality displayed
Status Official national standard — tailored to Singapore's haze context[__LINK_ICON] Independent systems — not directly comparable[__LINK_ICON]
NEA's Statement
- "No international guidelines on computation; each country designs to local needs"
- PSI not identical to US EPA AQI despite referencing it
- Comparisons will show inconsistent results — trust NEA's 24-hr PSI as official
⚠️ Health Guidance (PSI > 100 = Unhealthy)
- Healthy people: reduce prolonged/outdoor strenuous activity
- Those with heart/lung conditions: avoid such activity
Source: The Straits Times, Sep 15 2026 — https://str.sg/7yYH
Singapore 24-hr PSI Other AQI (e.g. aqicn.org, IQAir)
Calculation Based on 24-hour averages for all 6 pollutants[__LINK_ICON] Uses shorter averaging periods (1-hr) & different formulas
Pollutants PM2.5, PM10, SO₂, NO₂, O₃, CO — all measured by highly specialised, certified equipment[__LINK_ICON] May use NEA data + low-cost, less consistent sensors from private contributors[__LINK_ICON]
Result Generally lower/milder readings than AQI Often higher/poorer air quality displayed
Status Official national standard — tailored to Singapore's haze context[__LINK_ICON] Independent systems — not directly comparable[__LINK_I
CON]