Project CLEAN AIR
A Hong Kong government website concerning the air pollution situation in Hong Kong. It provides much useful information about the API, pollutants and effects.

AIRNow
A US cross agency government website that provides the AQI reading in the US. It also provides basic understanding and about the AQI and commonly asked questions with answer.

NEA
The Singapore National Environmental Agency website. Constant updates of the PSI readings in Singapore are provided there. A list of links there also provides much useful information about the PSI.

Department of Environment
The Malaysian government environmental website. Provides a informative figure on the API with their suggested action plan(s)

The Harbinger
Information on the Indonesian ISPU or Air Pollution Standard Index can be found here. Look under the segment Air Pollution Standard Index, Mobile Country | Technical Notes

PDF from Asian Development Bank
This is a very informative PDF Document that gives a good overview of the haze with details that elaborate on the causes and impacts. It also talks of the underlying causes and explains many much-used abbreviations.