The Difference Between PSI, AQI and PM2.5

As we struggle from the almost yearly cross-boundary haze from the Sumatran Islands, checking out the PSI to see if it was a good time to head out for a jog, or a swim, or even bring our children to the playground.

As many of us would have realised, why are there so many different numbers??? What do they all mean? Which one should I refer to?

Let us tell you the difference!

AIR QUALITY INDEX (AQI)

The AQI basically uses the American’s Environmental Protection Agency’s reporting system. It uses the latest particulate matter data instead of the 24-hour average.

Pollutant Standard Index (PSI)

PSI is an index of daily air quality levels, computed on the concentration of PM2.5 and other pollutants. In Singapore, we generally use the 24-hour PSI to plan for the day, and the hourly PM2.5 level to decide if we should engage in an immediate activity.

In essence, the AQI and PSI are the same thing except for these 2 differences:

A) AQI uses the USA Environmental Protection Agency’s system. PSI uses the local NEA system.

B) AQI uses the latest particulate matter data, PSI uses the 24-hour average.

PM2.5 reading

The first thing one would notice is that the numbers are very much smaller as compared to the AQI and the PSI numbers. However, PM2.5 is an important factor to consider when we are engaging for activities for the particular hour as it determines the amount of tiny particles in the air, that will harm our respiratory system, especially for children and people with respiratory problems.

On regular, non-hazy days, the PM2.5 in the air is usually about 20 - 35mcg. For our swimming lessons, we will continue to conduct classes until the PM2.5 level exceeds 150, or PSI exceeds 200, whichever comes first.

Have any other questions? Please feel free to leave us a comment!