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.

Contents 1 PSI in Singapore 2 PSI (API) in Malaysia 3 See also 4 References 5 External links

PSI in Singapore

The highest PSI reading on record in Singapore is 226 in September 1997.^[1] The PSI chart below is grouped by index values and descriptors, according to the National Environment Agency.[1]

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.

PSI (API) in Malaysia

The air quality in Malaysia is reported as the API or Air Pollution Index, which is based closely on the PSI.^[2] Four of the index's pollutant components (i.e., carbon monoxide, ozone, nitrogen dioxide and sulfur dioxide) are reported in ppmv but PM₁₀ particulate matter is reported in μg/m³.

Unlike the American AQI, the index number can exceed 500. Above 500, a state of emergency is declared in the reporting area. Usually, this means that non-essential government services are suspended, and all ports in the affected area closed. There may also be a prohibition on private sector commercial and industrial activities in the reporting area excluding the food sector.

See also

• Haze
• Air Quality Index
• Air Pollution Index
• 2006 Southeast Asian haze
• 1997 Southeast Asian haze
• 2010 Southeast Asian haze

References

External links

• FAQ on the haze
• 24-hourly PSI readings in Singapore
• Current PSI readings in Singapore