A haze of numbers? Here's your guide to decoding AQI, PM2.5 and PSI
As air quality in Singapore deteriorated over Monday (Sept 14), with all regions across Singapore recording 24-hour Pollutant Standard Index (PSI) readings in the unhealthy range, some netizens have wondered why official readings appear different from what they are seeing on other air quality platforms.One common question raised has been why the Republic does not use the Air Quality Index (AQI) that is publicly available from open sources such as the World Air Quality Index website (aqicn.org). The project, founded by a team of contributors in Beijing, computes an air quality index using the United States Environmental Protection Agency's (US EPA) Air Quality Index (AQI) reporting system.Meanwhile, in Singapore, the National Environment Agency (NEA) presents two key air quality measures on its haze microsite, namely the 24-hour Pollutant Standards Index (PSI) and the one-hour PM2.5 reading.