Air Pollution Index

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The Air Pollution Index (API) is a simple and generalized way to describe the air quality in Hong Kong and several other places in the world including Malaysia. It is in the form of an integer within 0 and 500, which is calculated from several sets of air pollution data.

The API is measured and reported by the Environmental Protection Department (EPD) daily in Hong Kong from June 1995. Moreover, the EPD makes forecast on the API for the following day everyday.

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

The table below shows the Health Implications of the respective API used in Hong Kong.

API	Air Pollution Level	Health Implications
0 - 25	Low	Not expected.
26 - 50	Medium	Not expected for the general population.
51 - 100	High	Acute health effects are not expected but chronic effects may be observed if one is persistently exposed to such levels.
100 - 200	Very High	People with existing heart or respiratory illnesses may notice mild aggravation of their health conditions. Generally healthy individuals may also notice some discomfort.
201 - 500	Very High	People with existing heart or respiratory illnesses may experience significant aggravation of their symptoms. There may also be widespread symptoms in the healthy population (e.g. eye irritation, wheezing, coughing, phlegm and sore throats).

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

0-50 Good
51-100 Moderate
101-200 Unhealthy
201-300 Very unhealthy
301- Hazardous

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.