Figure 1 : Air Pollution Index Flowchart

The ambient air quality measurement in Malaysia is described in terms of Air Pollutant Index (API). The API is developed in easily understood ranges of values as a means of reporting the quality of air instead of using the actual concentration of air pollutants. This index also reflects its effect on human health ranging from good to hazardous and also can be categorized according to the action criteria as stipulated in the National Haze Action Plan. The Malaysian API system closely follows the Pollutant Standard Index (PSI) developed by the United States Environmental Protection Agency (US-EPA)1.

The air pollutant index scale and terms used in describing the air quality levels are as in figure 1.

How is the API calculated ?

Following the requirement of the Malaysian  Ambient Air Quality Standard  (MAAQS) from the standpoint of human health implications, the pollutants was measured at varying averaging time according to WHO standard2. To determine the API for a given time period, the sub-index values (for all five air pollutants included in the API System) were calculated based on the average concentration calculated. The maximum sub-index of all five pollutants was selected as the API and the specific responsible air pollutants for the API value has to be reported to indicate the relevant health effect category and actions to be taken. The process flow chart for calculating API value at a given time was detailed in figure 2 below.

Figure 2: API calculation

What to do when API reach certain levels
More information on Daily Air Pollutant Index, and API archive.  References :