This article is about the air pollution index used in Malaysia. For air pollution indices in general, see Air quality index.

The Air Pollution Index (API) is a simple and generalized way to describe the air quality, which is used in Malaysia. It is calculated from several sets of air pollution data. It was formerly used in mainland China and Hong Kong. In mainland China the API was replaced by an updated Air Quality Index in early 2012 and on 30 December 2013 Hong Kong moved to a health based index.

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The air quality in Malaysia is reported as the API (Air Pollutant Index) or in Malay as IPU (Indeks Pencemaran Udara). Four of the index's pollutant components (i.e., carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide) are reported in ppmv but PM10 particulate matter is reported in μg/m3.

This scale below shows the Health classifications used by the Malaysian government.

API

Air Pollution Level

0 - 50 Good

51 - 100 Moderate

101 - 200 Unhealthy

201 - 300 Very unhealthy

301 - 500 Hazardous

500+ Emergency

If the API exceeds 500, a state of emergency is declared in the reporting area. Usually, this means that non-essential government services are suspended, and all ports in the affected area are closed. There may also be a prohibition on private sector commercial and industrial activities in the reporting area excluding the food sector.

The highest API value ever recorded was 839 in Kuching on 23 September 1997 during the 1997 Southeast Asian haze.

China's State Environment Protection Agency (SEPA) is responsible for measuring the level of air pollution in China. As of 28 August 2008, SEPA monitored daily pollution level in 86 of its major cities. The API level was based on the level of 5 atmospheric pollutants, namely sulfur dioxide (SO2), nitrogen dioxide (NO2), suspended particulates (PM10), carbon monoxide (CO), and ozone (O3) measured at the monitoring stations throughout each city.

API Mechanics
An individual score is assigned to the level of each pollutant and the final API is the highest of those 5 scores. The pollutants can be measured quite differently. SO2, NO2 and PM10 concentration are measured as average per day. CO and O3 are more harmful and are measured as average per hour. The final API value is calculated per day.

The scale for each pollutant is non-linear, as is the final API score. Thus an API of 100 does not mean twice the pollution of API at 50, nor does it mean twice as harmful. While an API of 50 from day 1 to 182 and API of 100 from day 183 to 365 does provide an annual average of 75, it does not mean the pollution is acceptable even if the benchmark of 100 is deemed safe. This is because the benchmark is a 24-hour target. The annual average must match against the annual target. It is entirely possible to have safe air every day of the year but still fail the annual pollution benchmark.

API and Health Implications (Daily Targets)

API Air Pollution
Level Health Implications

0 - 50 Excellent No health implications

51 -100 Good No health implications

101-150 Slightly Polluted Slight irritations may occur, individuals with breathing or heart problems should reduce outdoor exercise.

151-200 Lightly Polluted Slight irritations may occur, individuals with breathing or heart problems should reduce outdoor exercise.

201-250 Moderately Polluted Healthy people will be noticeably affected. People with breathing or heart problems will experience reduced endurance in activities. These individuals and elders should remain indoors and restrict activities.

251-300 Heavily Polluted Healthy people will be noticeably affected. People with breathing or heart problems will experience reduced endurance in activities. These individuals and elders should remain indoors and restrict activities.

300+ Severely Polluted Healthy people will experience reduced endurance in activities. There may be strong irritations and symptoms and may trigger other illnesses. Elders and the sick should remain indoors and avoid exercise. Healthy individuals should avoid out door activities.

The API was in use in Hong Kong from June 1995 to December 2013. It was measured and updated hourly by the Environmental Protection Department (EPD). Moreover, the EPD made forecasts of the API for the following day everyday.

The API was based on the level of 6 atmospheric pollutants, namely sulfur dioxide (SO2), nitrogen dioxide (NO2), respirable suspended particulates, carbon monoxide (CO), ozone (O3), lead (Pb), measured at all the monitoring stations throughout the territory. It was replaced by the Air Quality Health Index on the 30th December 2013.

There are 11 General Stations and 3 Roadside Stations. The former includes Central / Western, Eastern, Kwai Chung, Kwun Tong, Sha Tin, Sham Shui Po, Tai Po, Tap Mun, Tsuen Wan, Tung Chung, and Yuen Long; the latter Causeway Bay, Central, and Mong Kok.

In Hong Kong, there were two types of API: General API and Roadside API. The EPD reported the latest APIs hourly.