What You Should Know

What is PSI?

PSI stands for Pollutant Standards Index , it's an index to provide accurate and easy to understand information about daily levels of air quality. PSI is computed based on the 24-hour average of PM2.5 concentration levels, among other pollutants.

PM refers to particulate matter and PM2.5 is the dominant pollutant during haze episodes.

6 pollutant parameters that determine PSI level:

  • Particulate Matter (PM 10 )
  • Fine Particulate Matter (PM 2.5 )
  • Sulphur dioxide
  • Nitrogen dioxide
  • Ozone
  • Carbon monoxide

What's the difference between 24-hour PSI and 1-hour PM 2.5 concentration readings?

The 24-hour PSI is based on readings taken over the past 24 hours. Whereby, the 1-hour PM 2.5 concentration readings are only an indicative measure of the current air quality.

There are four bands on the PM2.5 concentration scale: 0 to 55 for normal, 56 to 150 for elevated, 151 to 250 for high, and very high for any higher readings.

Why 1-hour PSI based on PM 2.5 concentration reading matters?

According to NEA, PM 2.5 concentration readings are a better indicator ofcurrent air quality condition. It provides near real time information so you could plan immeddiate outdoor activities, such as jogging.