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Pollutant Standards Index: Map


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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 Singaporemarker is 226 in September 1997. The PSI chart below is grouped by index values and descriptors, according to the National Environment Agency.[363508]

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.

See also


  1. "Haze worsens in Singapore, PSI reading hits 126", Daniel Tan, Channel NewsAsia, 07 October 2006

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