Haze: Visibility distance and API readings may not match

She said this was due to the visibility distance measured real time while API readings are updated in 24 hours and as such the two measurements do not match.

"Even though the haze may seemed bad with the naked eye, its concentration could be lower due to high water vapour.

"This is because the particles have been absorbed and can block sunlight, causing a lower visibility distance," she told a special workshop for the media titled "Challenges of the Natural Resources Ministry in Sustainable Management of Natural Resources and Environment" here today.

The workshop was also attended by Deputy Natural Resources and Environment Minister Datuk Hamim Samuri and DOE director-general Datuk Halimah Hassan. Meanwhile, Halimah at a media conference later, said DOE is expected to implement the measuring of finer particulate matter of less than 2.5 micrometres (PM2.5) in API readings compared to PM10 now by 2017.

She said 12 air quality monitoring stations which could measure at the PM2.5 level had been set up in several areas nationwide.

"API measurement based on PM2.5 will give a higher reading compared to API based on PM10. Nonetheless the reading scale to determine the API status of good, moderate, unhealthy, very unhealthy and hazardous is the same in both readings," she said.

On the difference between the API reading in Johor and the Pollutant Standards Index (PSI) in Singapore, Halimah clarified that the republic has been implementing the PSI based on particles less than PM2.5 since April 1, 2014.

In this regard, Halimah advised the people to only refer to the applications provided and recognised by DOE in current API readings to avoid confusion and the problem of different readings.