Various air quality indicators can guide activity planning

We thank Ms Tan Lay Hoon for her suggestions ("Half-hour PSI readings more useful for event organisers"; Monday).

The National Environment Agency (NEA) has been providing hourly, real-time haze information on our various platforms.

Since April 1 last year, the 24-hour Pollutant Standards Index (PSI), three-hour PSI and PM2.5 concentrations have been published hourly, on the hour, on the NEA website, the haze microsite (

haze-updates/pollutant-concentrations) and our myENV mobile application.

During periods of transboundary haze, the primary pollutant determining the PSI level is fine particulate matter, or PM2.5.

Only the 24-hour PSI value has a corresponding Ministry of Health health advisory, because scientific and epidemiological studies on the health effects of exposure to particulate matter have been based on this duration of exposure.

The forecast of 24-hour PSI range, which is issued by NEA every evening, and the corresponding health advisory can be used to plan ahead, such as one's activities for the next day. For a guide to more immediate activities, the three-hour PSI and one-hour PM2.5 concentration levels can be used as an indicative measure to make adjustments to daily activities.

For example, if the three-hour PSI and one-hour PM2.5 concentration levels are high, people may wish to postpone strenuous outdoor activities, such as jogging.

The health impact of air pollution is related to concentration levels of pollutants, the duration of exposure, as well as the health status and level of activity of the individual.

For more information or updates, members of the public may visit our NEA website ( or the haze microsite (, follow us on Twitter (@NEAsg) and Facebook (

NEASingapore), or download the myENV application.

Fong Peng Keong

Director, Pollution Control Department

National Environment Agency

A version of this article appeared in the print edition of The Straits Times on September 19, 2015, with the headline 'Various air quality indicators can guide activity planning'. Print Edition | Subscribe