This topic falls under a sensitive category and is presented descriptively and neutrally.
The Air Pollutant Index (API), or Indeks Pencemar Udara (IPU), is a number from 0 upward issued by the Department of Environment (DOE) to indicate the air-quality status of an area. It is calculated from six pollutants — SO2, NO2, CO, O3, PM10 and PM2.5 — with each converted into a 'sub-index', and the highest sub-index in that hour becomes the API reading. That value is then mapped to six health categories, from Good (0–50) to Hazardous (above 300).
- The API is calculated from six pollutants; the highest sub-index in that hour becomes the official API reading.
- PM2.5 (fine particulate matter) was added to the API calculation from 2017; fine particulates are usually the dominant pollutant during haze.
- Six categories: Good (0–50), Moderate (51–100), Unhealthy (101–200), Very unhealthy (201–300), Hazardous (>300) and Emergency (>500).
- Pollutant concentrations are measured by 52 automatic (CAQM) stations and 14 manual stations across Malaysia.
- The API calculation is based on the Pollution Standard Index (PSI) adopted by the USEPA.
Who this applies to: Parents, teachers, athletes, the elderly, pregnant women, children, people with heart or lung complications, and anyone planning outdoor activities, especially during the haze season.
On this page
When the haze thickens and schools start asking whether the morning assembly should be cancelled, a single number usually settles it — the API reading. That figure looks simple, but behind it lie six continuously measured pollutants and a formula that filters them all into one value.
What does the API actually measure?
The Air Pollutant Index (API) is an indicator of the air-quality status of an area. The Department of Environment (DOE) calculates it based on six main pollutants, each averaged over a different time period because the safe exposure limit for each one is not the same:
- Sulfur dioxide (SO2) — 1-hour average
- Nitrogen dioxide (NO2) — 1-hour average
- Carbon monoxide (CO) — 8-hour average
- Ozone (O3) — 8-hour and 1-hour averages
- Fine particulates PM10 — 24-hour average
- Fine particulates PM2.5 — 24-hour average, added to the calculation from 2017
How do six pollutants become one number?
The average concentration of each pollutant is standardised through a specific mathematical formula to produce a unitless value called a sub-index. Each pollutant produces its own sub-index, and the highest sub-index in that hour is taken as the API reading. This method is based on the Pollution Standard Index (PSI) adopted internationally by the United States Environmental Protection Agency (USEPA).
For example, for PM2.5 in the best range (0–50), the formula is API = 4.1667 × X, where X is the 24-hour average of PM2.5 in µg/m³. Higher concentrations use a different segment of the formula. In practice, fine particulates are usually the dominant pollutant — so during haze, the API reading is almost always driven by PM10 or PM2.5.
What does each category mean for your health?
The API is mapped to six colour-coded categories. This is the part that matters most for daily decisions:
| API | Status | Colour | Health advice |
|---|---|---|---|
| 0–50 | Good | Blue | No restrictions on outdoor activity; maintain a healthy lifestyle |
| 51–100 | Moderate | Green | No restrictions on outdoor activity; maintain a healthy lifestyle |
| 101–200 | Unhealthy | Yellow | Sensitive groups (the elderly, pregnant women, children, people with heart/lung complications) should limit outdoor activity; the general public should reduce vigorous activity |
| 201–300 | Very unhealthy | Orange | The elderly and high-risk individuals should stay indoors and reduce physical activity; those with health complications should see a doctor |
| >300 | Hazardous | Red | The elderly and high-risk individuals are prohibited from outdoor activity; the general public should avoid outdoor activity |
| >500 | Emergency | — (no separate colour defined on the official gauge) | Follow the directives of the National Security Council and mass-media announcements |
Where does this data come from?
Readings are not taken from a single place. The DOE operates the National Air Quality Monitoring Network, which comprises 52 automatic stations — Continuous Air Quality Monitoring (CAQM) stations — and 14 manual stations that use high-volume samplers (HVS). These stations are placed at strategic locations covering industrial, urban, suburban and rural areas across the Peninsula, Sabah and Sarawak, so that readings represent the air people actually breathe.
What’s next
Before planning outdoor activities during haze, check the latest official API reading for your area through the DOE’s official online monitoring system, rather than figures circulating without a source on social media. If you fall into a sensitive group — the elderly, pregnant women, children, or people with heart or lung complications (including conditions such as asthma) — start taking precautions once the reading passes 100, rather than waiting for it to reach Hazardous. To understand what drives these spikes in readings, see the related pages on haze in Malaysia and the role of the Department of Environment.
Does an API reading of 100 mean the air is 'half polluted'?
No. The API is not a percentage. A reading of 0–50 means Good and 51–100 means Moderate — both with no restrictions on outdoor activity. Readings become a concern once they pass 100 (Unhealthy), and above 300 is considered Hazardous.
Which pollutant most often determines the API reading?
Fine particulates — PM10 and PM2.5 — are the dominant pollutant most of the time, especially when haze occurs in Malaysia. During those periods the API reading is usually driven by the fine-particulate sub-index.
At what reading should I avoid outdoor activity?
At 101–200 (Unhealthy), sensitive groups — the elderly, pregnant women, children, and people with heart or lung complications — should limit outdoor activity. Above 300 (Hazardous), the elderly and high-risk individuals are prohibited from outdoor activity, and the general public is advised to avoid it.
The following are deliberately unstated or described only qualitatively until confirmed by a subject-matter expert:
- Asma tidak dinamakan secara khusus dalam kedua-dua PDF JAS yang dirujuk (sumber menyebut warga tua, wanita hamil, kanak-kanak dan komplikasi jantung/paru-paru). Rujukan asma di sini ialah inferens editorial sebagai keadaan paru-paru — sahkan dengan sumber nasihat kesihatan rasmi JAS.
- Band Kecemasan (>500) tidak diberi warna berasingan pada tolok rasmi JAS (warna hanya ditakrifkan sehingga Merbahaya). Sahkan sama ada satu warna rasmi wujud untuk band ini sebelum menetapkannya.
- Nama dan alamat portal bacaan langsung (APIMS di apims.doe.gov.my) tidak didokumenkan dalam kedua-dua PDF yang dirujuk. Sahkan nama serta URL portal rasmi semasa untuk bacaan IPU langsung.
Sources
- Pengiraan Indeks Pencemar Udara (IPU) / Air Pollutant Index (API) Calculation — Jabatan Alam Sekitar (Department of Environment)
- General Information of Air Pollutant Index (API) — Jabatan Alam Sekitar (Department of Environment)
- Air Pollution Index — What to do when API reach certain levels — Jabatan Alam Sekitar (Department of Environment)
Change history
| Version | Date | Change | By |
|---|---|---|---|
| 01.00 | 28 Jul 2026 | Approved and published. | — |