A haze reading on 24 September from AQICN shows the discrepancy between Malaysia and Singapore's haze index.
A haze reading on 24 September from AQICN shows the discrepancy between Malaysia and Singapore’s haze index. Photo via Olivier Falcoz.

As another round of heavy haze covered parts of Malaysia over the weekend, many citizens started to wonder if the API readings accurately reflected the situation. On social media, an image showing much lower readings in Malaysia than Singapore seemed to suggest there was a disconnect between how each country measures haze. Kelana Jaya MP Wong Chen went on to criticise Malaysia’s methods. So can we trust API readings?

What is the difference between API and PSI?

Singapore uses the PSI (Pollutant Standards Index), a standard developed for measuring pollutants by the United States Environmental Protection Agency (USEPA). Malaysia uses API (Air Pollutant Index). Both have similar categories: a reading of 0-50 is considered ‘good’, 51- 100 ‘moderate’, 101-200 ‘unhealthy’, 201-300 ‘very unhealthy’. A reading above 300 is ‘hazardous’.

How does Malaysia measure the haze?

API readings take five things into account: ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2) and sulphur dioxide (SO2), as well as the concentration of 10 microns (PM10) particulates in the air. The pollutant with the highest concentration is then taken as the API reading and this is usually PM10.

How is this different from Singapore?

Singapore has an additional measure of smaller particulates, 2.5 microns (PM2.5), as well as the measures taken into account by Malaysia. The government believes that PM2.5 is the “main pollutant of concern” during haze periods. The addition of a PM2.5 measure means that Singapore has seen higher readings of haze.

Will Malaysia change its system?

Apparently, there are plans to change the measurement system in 2016 in line with new Malaysian Air Quality Guidelines. However, Wong Chen pointed out that the Department of Environment already has data on PM2.5 and urged the government to start publishing this data to keep the public fully informed.

So can we rely on API readings?

Keep an eye on API readings but know that smaller particles are not taken into account. It’s also worth noting that even the latest and most comprehensive API or PSI data will always be an approximation, since it takes about an hour to retrieve the data and the reading is based on an average. Weather fluctuations may cause the haze in any area to change quickly. The government will continue to make decisions for school closures and cloud seeding based on the API.

If you want to compare Malaysia’s readings with Singapore’s, then you can head to www.aqicn.org or Singapore’s haze website.

Find out more about at www.apims.doe.gov.my

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