# Air Pollutant Index (API): How Malaysia Measures Air Quality

> The API reading you see during a haze episode is a single number distilled from six pollutants. This guide explains how it is calculated, the network of monitoring stations that produce it, and what each category means — from Good to Hazardous — for your health.

- Category: environment
- Language: en
- Status: published
- Updated: 2026-07-28
- Canonical: https://negaraku.md/en/environment/air-pollutant-index-api-malaysia

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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.

## Sources

- Pengiraan Indeks Pencemar Udara (IPU) / Air Pollutant Index (API) Calculation — https://www.doe.gov.my/wp-content/uploads/2021/09/API_Calculation.pdf (Jabatan Alam Sekitar (Department of Environment))
- General Information of Air Pollutant Index (API) — https://www.doe.gov.my/wp-content/uploads/2021/10/General-Information-of-Air-Pollutant-Index.pdf (Jabatan Alam Sekitar (Department of Environment))
- Air Pollution Index — What to do when API reach certain levels — https://www.doe.gov.my/en/air-pollution-index/ (Jabatan Alam Sekitar (Department of Environment))

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