Haze Day PSI vs API vs ISPU vs AQI: Southeast Asia's air-quality scales compared
Updated · Every figure links to its source below.
Singapore's PSI, Malaysia's API and Indonesia's ISPU use the same band edges (50, 100, 200, 300) and all call readings above 100 Unhealthy, but each is calculated from its own pollutants and breakpoints. The US AQI shown by most global apps is stricter for PM2.5, so the same air usually gives a higher US AQI number. Compare like with like, and follow your local official index.
Key facts
- Singapore (PSI), Malaysia (API) and Indonesia (ISPU) all start the Unhealthy band at an index value of 101.
- Since May 2024 the US AQI rates a 24-hour PM2.5 of 35.5 µg/m³ or more as Unhealthy for Sensitive Groups.
- The WHO's 2021 guideline for 24-hour PM2.5 is 15 µg/m³ and for the annual mean 5 µg/m³.
- Malaysia's Education Ministry closes schools where the API is above 180, or above 150 for three days in a row (rule announced 8 October 2026).
- Thailand cut its 24-hour PM2.5 standard from 50 to 37.5 µg/m³ on 1 June 2023.
Why apps show different numbers for the same air
- Different index: a US AQI, a PSI and an API turn the same PM2.5 concentration into different scores.
- Different averaging: a 1-hour reading reacts within the hour; a 24-hour average lags by many hours.
- Different data: official reference stations, low-cost sensors and atmospheric models can disagree, especially in thick smoke.
- Different place: a regional or national figure is not your street; NEA reports five regions and Malaysia reports each station.
The scales at a glance
| Index | Publisher | Pollutants | Updated | Unhealthy from |
|---|---|---|---|---|
| PSI | Singapore: National Environment Agency (NEA) | 6: PM2.5, PM10, SO2, CO, O3, NO2 (PM2.5 added April 2014) | Hourly, 24-hour rolling, 5 regions | 101 |
| API / IPU | Malaysia: Department of Environment (DOE) | 6: PM2.5, PM10, SO2, NO2, O3, CO (PM2.5 included since 2018) | Hourly, per station | 101 |
| ISPU | Indonesia: environment ministry | 7: PM10, PM2.5, CO, NO2, SO2, O3, HC (PM2.5 added 2020) | PM2.5 hourly; others at least twice a day | 101 |
| AQI (TH) | Thailand: Pollution Control Department (PCD) | 6: PM2.5, PM10, O3, CO, NO2, SO2 | Hourly | 101 |
| VN_AQI | Vietnam: Vietnam Environment Administration | Must include PM10 or PM2.5 | Hourly | 101 |
| US AQI | United States: EPA (shown by many global apps) | 6: PM2.5, PM10, O3, CO, SO2, NO2 | Hourly | 101 (sensitive groups), 151 (everyone) |
Each index takes the highest of its pollutant sub-indices. During haze PM2.5 almost always sets the number.
Band names side by side
| Index value | PSI (SG) | API (MY) | ISPU (ID) | US AQI | Thai AQI |
|---|---|---|---|---|---|
| 0–50 | Good | Good | Good (Baik) | Good | 0–25 Very good; 26–50 Good |
| 51–100 | Moderate | Moderate | Moderate (Sedang) | Moderate | Moderate |
| 101–150 | Unhealthy | Unhealthy | Unhealthy (Tidak Sehat) | Unhealthy for Sensitive Groups | Starting to affect health |
| 151–200 | Unhealthy | Unhealthy | Unhealthy (Tidak Sehat) | Unhealthy | Starting to affect health |
| 201–300 | Very Unhealthy | Very Unhealthy | Very Unhealthy (Sangat Tidak Sehat) | Very Unhealthy | Affecting health |
| 301+ | Hazardous | Hazardous | Hazardous (Berbahaya) | Hazardous | Affecting health |
Matching names do not make the numbers interchangeable: pollutants, averaging periods and concentration breakpoints differ. NEA itself says its 24-hour PSI is not comparable with readings on third-party sites.
The US AQI for PM2.5, as most global apps show it
The US EPA tightened its PM2.5 breakpoints in 2024. They apply to a 24-hour average; apps often feed them a 'NowCast' that weights recent hours more heavily.
| AQI | Category | PM2.5 (µg/m³) |
|---|---|---|
| 0–50 | Good | 0–9.0 |
| 51–100 | Moderate | 9.1–35.4 |
| 101–150 | Unhealthy for Sensitive Groups | 35.5–55.4 |
| 151–200 | Unhealthy | 55.5–125.4 |
| 201–300 | Very Unhealthy | 125.5–225.4 |
| 301–500 | Hazardous | 225.5–325.4 |
Singapore's 1-hour PM2.5 bands
Alongside the 24-hour PSI, NEA publishes 1-hour PM2.5 concentrations in four bands. Because they react within the hour, sports organisers, schools and Haze Day's advice use them for decisions about the next few hours.
| Band | Descriptor | 1-hour PM2.5 (µg/m³) |
|---|---|---|
| I | Normal | 0–55 |
| II | Elevated | 56–150 |
| III | High | 151–250 |
| IV | Very High | ≥251 |
PM2.5 standards: how strict is each benchmark?
| Benchmark | 24-hour | Annual |
|---|---|---|
| WHO guideline (2021) | 15 | 5 |
| WHO interim target 1 (2021) | 75 | 35 |
| United States, EPA standard (2024) | 35 | 9.0 |
| Singapore, 2020 target | 37.5 | 12 |
| Singapore, long-term target | 25 | 10 |
| Malaysia, ambient standard (2020) | 35 | 15 |
| Thailand, standard (from 1 June 2023) | 37.5 | 15 |
| Indonesia, ambient standard (PP 22/2021) | 55 | 15 |
Health effects have been found below every one of these limits; the WHO sets no level that is completely safe.
When the index triggers action
- Malaysia: from 8 October 2026 the Education Ministry closes schools in areas where the DOE records an API above 180, or above 150 for three days in a row, and moves lessons online (PdPR). The previous rule was an API above 200.
- Singapore: NEA issues daily haze advisories once the 24-hour PSI enters the Unhealthy range (above 100). The Haze Task Force said school closures would be considered if the next day's 24-hour PSI is forecast above 300 (CNA, 9 October 2026).
- Sports: many youth leagues in Singapore stop play when the 1-hour PM2.5 is above 110 µg/m³. That is a league policy, not an NEA rule.
Quick answers
Is Singapore's PSI the same as the AQI?
No. The PSI is Singapore's own index from NEA. It shares band edges with Malaysia's API but not with the US AQI, which starts Unhealthy for Sensitive Groups at 101 and uses stricter PM2.5 breakpoints. Do not compare a PSI with a US AQI number directly.
Why does my weather app show a higher number than NEA or the DOE?
Most global apps show the US AQI, which turns the same PM2.5 into a higher score, and many use a short 'NowCast' average, a nearby low-cost sensor or a model. For official decisions in Singapore and Malaysia, use NEA's PSI and 1-hour PM2.5 or the DOE's API.
What PM2.5 level is safe?
There is no level with zero risk. The WHO's 2021 guideline is 15 µg/m³ over 24 hours and 5 µg/m³ as an annual mean. For day-to-day decisions in Singapore, NEA's 1-hour Normal band is 0–55 µg/m³.
Related questions
More reference pages
References
- Air pollution FAQs (PSI, PM2.5 and comparability). National Environment Agency, Singapore.
- 1-hr PM2.5 readings and bands. NEA haze.gov.sg.
- Clean air: Singapore's air quality targets. Ministry of Sustainability and the Environment, Singapore.
- About the Air Pollutant Index. Department of Environment Malaysia (APIMS).
- Jerebu: sekolah ditutup jika IPU lebih 180 (KPM). Portal Berita RTM, 2026.
- Peraturan Menteri LHK P.14/2020 tentang Indeks Standar Pencemar Udara. Republic of Indonesia (JDIH), 2020.
- New PM2.5 standard of 37.5 µg/m³. Pollution Control Department, Thailand, 2023.
- Reconsideration of the National Ambient Air Quality Standards for Particulate Matter. US Federal Register, 2024.
- What are the WHO Air Quality Guidelines?. World Health Organization, 2021.
Sources
- NEA 24-hour PSI (Singapore) — National Environment Agency (NEA), Singapore · official site · API / docs
- NEA 1-hour PM2.5 readings (Singapore) — National Environment Agency (NEA), Singapore · official site · API / docs
- Malaysia DOE APIMS / MyJAS — Department of Environment Malaysia (DOE) · official site
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Haze Day. “PSI vs API vs ISPU vs AQI: Southeast Asia's air-quality scales compared.” haze.day, updated . https://haze.day/en/learn/air-quality-indices
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