Pollutant Standards Index

The Pollutant Standards Index, or PSI, provides a uniform system of measuring pollution levels for the major air pollutants. It is based on a scale devised by the United States Environmental Protection Agency (USEPA) to provide a way for broadcasts and newspapers to report air quality on a daily basis.

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 in Singapore
The highest PSI reading on record in Singapore is 226 in September 1997. The PSI chart below is grouped by index values and descriptors, according to the National Environment Agency.

Note: This chart reflects those shown in Singapore and may differ for other countries.