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Different air quality indicators put question on which index is better to monitor air quality in SG.

Did you know that the Pollutant Standards Index (PSI) reached a record high of 401 ppm in 2013? So how do we use PSI to decide what activities to do throughout a day?


To understand PSI, we have to first understand what PM stands for. PM (particulate matter) is a major component of haze. It comprises soot, carbon dioxide and other toxic pollutants like sulphur dioxide. PSI is essentially an index used to monitor the level of atmospheric pollutants. There are 4 main levels of PM:


Normal (0 - 55)

Elevated (56 - 150)

High (151 - 250)

Very high (>=251)


These readings are arbitrarily measured in µg/m³ and they reflect the 1-hr PM2.5 reading. NEA provides 2 kinds of air quality indices– the 24-hour PSI and the 1-hour PM2.5. The former, which includes both PM10 and PM2.5 is measured over a day and helps us schedule future itineraries. On the other hand, the latter fluctuates more easily over time and can be used to gauge immediate activities, such as whether it is ok to go for a jog. Both air quality indices can be used depending on the time and type of activities that we plan to do.


Some of you rely on another air quality indicator widely used– World Air Quality Index (AQI). However, you might have realised that there is a slight disparity between the measurements of PSI and AQI. That is because both indicators follow different methodologies of measuring the air quality. AQI follows the United States Environmental Protection Agency’s (EPA’s) reporting system that relies on the average PM2.5 concentration data while PSI follow’s Singapore NEA’s 24 hour average data reporting system. While both air quality indices are suitable for tracking air quality, we would highly recommend following NEA’s PSI as it would be more apt for local air quality monitoring. It is imperative that we stay notified of the air quality to reduce the risks of exposure to harmful air pollutants during episodes of haze.


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