The PSI is reported as a number on a scale of 0 to 500 and is the air quality indicator. These index figures enable the public to determine whether the air pollution levels in a particular location are good, unhealthy, hazardous or worse. The PSI is used in a number of countries including the United States and Singapore. However, since 1999, the United States EPA has replaced the Pollution Standards Index (PSI) with the Air Quality Index (AQI) to incorporate new PM2.5 and ozone standards.
|PSI||Descriptor||General Health Effects|
|0 - 50||Good||None|
|51 - 100||Moderate||Few or none for the general population|
|101 - 200||Unhealthy||Mild aggravation of symptoms among susceptible persons i.e. those with underlying conditions such as chronic heart or lung ailments; transient symptoms of irritation e.g. eye irritation, sneezing or coughing in some of the healthy population.|
|201 - 300||Very Unhealthy||Moderate aggravation of symptoms and decreased tolerance in persons with heart or lung disease; more widespread symptoms of transient irritation in the healthy population.|
|301 - 400||Hazardous||Early onset of certain diseases in addition to significant aggravation of symptoms in susceptible persons; and decreased exercise tolerance in healthy persons.|
|Above 400||Hazardous||PSI levels above 400 may be life-threatening to ill and elderly persons. Healthy people may experience adverse symptoms that affect normal activity.|
Note: This chart reflects those shown in Singapore and may differ for other countries.