Why can the hourly haze reading say one thing while the PSI says another? They measure different things.
The 1-hr PM2.5 reading (µg/m³) shows fine particles in the past hour. The 24-hr PSI is an index that looks back over 24 hours, so it rises and falls more slowly.
Example from NEA readings for Singapore’s South region, 21–23 Sep 2019 (times SGT):
• 21 Sep, 1am: 1-hr PM2.5 was 105 µg/m³ (Elevated), while the 24-hr PSI was 75 (Moderate).
• 23 Sep, 3am: the 24-hr PSI peaked at 129 (Unhealthy), while 1-hr PM2.5 had fallen to 63 µg/m³ (Elevated).
• 23 Sep, 5pm: 1-hr PM2.5 was 43 µg/m³ (Normal), while the 24-hr PSI was still 110 (Unhealthy).
• Today, 14 Oct 2026, 1pm reading: 1-hr PM2.5 was 173 µg/m³ (High) in the South region (US-style AQI 248, Very Unhealthy), while the 24-hr PSI was 131 (Unhealthy).
Peak 1-hr PM2.5 so far on 14 Oct 2026, as of 7pm (NEA via data.gov.sg; US-style AQI = US EPA 2024 scale applied to the 1-hr reading):
• West, 3pm: 288 µg/m³ (Very High), US-style AQI 425 (Hazardous)
• Central, 7pm: 229 µg/m³ (High), US-style AQI 308 (Hazardous)
• East, 3pm: 208 µg/m³ (High), US-style AQI 283 (Very Unhealthy)
• South, 4pm: 190 µg/m³ (High), US-style AQI 265 (Very Unhealthy)
• North, 3pm: 140 µg/m³ (Elevated), US-style AQI 215 (Very Unhealthy)
How NEA suggests using them: the 1-hr PM2.5 helps with what you’re doing right now. For planning the next day, use NEA’s 24-hr PSI forecast and its health advisory. Check the hourly PM2.5, not just the PSI. Current readings: haze.gov.sg.
In the US, the official AQI for PM2.5 also uses a 24-hour average. AirNow’s hourly figure is the NowCast, a 12-hour weighted estimate.
All numbers: NEA readings via data.gov.sg (South region for 2019 and 14 Oct 1pm; all five regions for the 14 Oct peaks). This is an explainer about how the readings work, not a current air-quality report.
Sources:
• NEA via data.gov.sg (PM2.5 and PSI, 21–23 Sep 2019):
PM2.5: | |
PSI: | |
• NEA via data.gov.sg (14 Oct 2026): |
• NEA haze site (1-hr PM2.5 bands, PSI descriptors):
• NEA air pollution FAQs:
• NEA, Managing Haze:
• NEA/MOH, 13 Jul 2020, 1-hr PM2.5 personal guide:
• US EPA, AQI Technical Assistance Document:
• US EPA, PM NAAQS AQI fact sheet:
• US EPA, NowCast fact sheet:
• Traffic camera image: LTA camera 4798, Telok Blangah, 14 Oct 2026, via data.gov.sg (Singapore Open Data Licence v1.0).
Art: AI-generated webtoon illustrations (altered/synthetic label on). Music: original, generated for this video.
#haze #Singapore #AirQuality
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Sources for this Short:
1. NEA readings, South region, 21–23 Sep 2019 (data.gov.sg):
PM2.5: https://api.data.gov.sg/v1/environment/pm25?date=2019-09-21 | https://api.data.gov.sg/v1/environment/pm25?date=2019-09-22 | https://api.data.gov.sg/v1/environment/pm25?date=2019-09-23
PSI: https://api.data.gov.sg/v1/environment/psi?date=2019-09-21 | https://api.data.gov.sg/v1/environment/psi?date=2019-09-22 | https://api.data.gov.sg/v1/environment/psi?date=2019-09-23
2. NEA haze site, PM2.5 bands and PSI descriptors: https://www.haze.gov.sg/resources/1-hr-pm2.5-readings
3. NEA FAQs (24-hr PSI and health advisories): https://www.nea.gov.sg/our-services/pollution-control/air-pollution/faqs
4. NEA/MOH, 13 Jul 2020 (1-hr PM2.5 guide): https://www.nea.gov.sg/media/news/news/index/new-personal-guide-based-on-1-hr-pm2.5-concentration-readings-to-guide-the-public-during-haze-season
5. US EPA AQI TAD: https://document.airnow.gov/technical-assistance-document-for-the-reporting-of-daily-air-quailty.pdf
6. US EPA NowCast: https://www.epa.gov/sites/default/files/2018-01/documents/nowcastfactsheet.pdf
7. NEA readings, South region, 14 Oct 2026, 1pm: 1-hr PM2.5 173 µg/m³ (High), 24-hr PSI 131 (Unhealthy): https://api.data.gov.sg/v1/environment/pm25?date=2026-10-14 | https://api.data.gov.sg/v1/environment/psi?date=2026-10-14
8. Traffic camera image: LTA camera 4798, Telok Blangah, 14 Oct 2026, via data.gov.sg (Singapore Open Data Licence v1.0).
For live readings: https://www.haze.gov.sg/