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Mythbuster on air quality reporting in Malaysia and Singapore

Air Quality Index (AQI) 2015-09-23

Air Quality Index (AQI) 2015-09-23 #1

Picture is sourced from

It’s interesting and perplexing to note that air quality index in Johor Baru is moderate yellow alert while Singapore is unhealthy orange alert on 23 September 2015 from the information published at (

The narrow Tebrau Strait should not be a physical barrier for air current flow in the atmosphere between Johor Baru and Singapore. Do not be misled to believe that air quality in Johor Baru is better than Singapore on that day.

The difference in readings and alert flags is mainly due to the different methodology used by both countries.

PM2.5 is more critical in air quality measurement

Singapore is using PSI (The Pollutant Standards Index) to issue air quality warning or alert to public members. The PSI is based on a scale devised by the United States Environmental Protection Agency (USEPA) which included fine particulate matter (PM2.5) since 1 April 2014.

Singapore PSI is taking into account PM2.5 particulates while Malaysia AQI (a.k.a API) is only measuring PM10 particulates. PM2.5 particulates (<2.5 micron) are more harmful than PM10 particulates (<10 micron) for their smaller size which can go deeper and absorb into the bloodstream through the lungs.

For the most cities with pollution from transport and other combustion sources, PM2.5 concentration is higher in the PM10 fraction. This is one of the important reasons for WHO to push for all countries to have standards for PM2.5.

Generally, API based on PM10 is much lower than PSI for air quality in Malaysia and Singapore. An example is taken from data on air quality in Singapore on 23 September; PSI is 135, PM2.5 (AQI) is 179 and PM10 (AQI) is 59.

Under such circumstance, Singapore would declare unhealthy for air quality based on PSI 135 while Malaysia would declare air quality is moderate based on PM10(AQI) 59.

I urge Malaysia Department of Environment DOE to publish PM2.5 to reflect the actual air quality rather than giving a “false safe” indicator. Those people sensitive to PM2.5 particulates like heart disease and asthma patients can take proactive or necessary measures to fend off themselves with PM2.5 API indicator like to wear N95 face mask and stay indoor.

If you are heart disease patient or anyone care about own health, I suggest get a quality face mask from 3M. The face mask I used is a bit pricey at RM5 per piece (plus RM3 for shipping fee) for its breathable outlet design. The normal N95 face mask will choke down you breath after long hours of usage.

nk khoo with face mask

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