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The Air Quality Index ('''AQI''') is a Standard ized indicator of the Air Quality in a given location. It measures mainly Ground-level Ozone and Particulate s (except the Pollen Count ), but may also include Sulphur Dioxide , and Nitrogen Dioxide . Various agencies around the world measure such indices, though definitions may change between places.

The U.S. Environmental Protection Agency and the Meteorological Service Of Canada differ on what AQI structure and health classification is used:

Health classifications used by the EPA:

  • 0-50: Good (green)

  • 51-100: Moderate (yellow)

  • 101-150: Unhealthy for sensitive groups (orange)

  • 151-200: Unhealthy (red)

  • 201-300: Very unhealthy (purple)

  • 301-500: Hazardous (maroon)


Health classifications used by the MSC:

  • 0-25---: Good (green)

  • 26
    50: Moderate (yellow)

  • 51-100: Poor (orange/red)

  • 101+: Very poor (purple)


In Ontario , 31 is the upper limit for good and 32 the lower limit for moderate.

The AQI can worsen (go up) due to lack of dilution with fresh air. Stagnant air, often caused by an Anticyclone or Temperature Inversion , or other lack of Wind s lets Air Pollution remain in a local area. On these days, the News Media may ask the Public to Carpool or use Public Transport , or take other air pollution prevention measures such as Teleworking .




OTHER INDEXES



United Kingdom


The Met Office of the United Kingdom (UK) issues air quality forecasts wherein the level of pollution is described either as an index (ranging from 1 to 10) or as a banding (low, moderate, high or very high). These levels are based on the health effects of each pollutant.

The forecast is produced for a number of different pollutants and their typical health effects are shown in the following table.


Hong Kong


The Air Pollution Index (API) levels for Hong Kong are related to the measured concentrations of ambient respirable suspended particulate (RSP), sulphur dioxide (SO2), carbon monoxide (CO), ozone (O3) and nitrogen dioxide (NO2) over a 24-hour period based on the potential health effects of air pollutants.

An API level at or below 100 means that the pollutant levels are in the satisfactory range over 24 hour period and pose no acute or immediate health effects. However, air pollution consistently at "High" levels (API of 51 to 100) in a year may mean that the annual Hong Kong "Air Quality Objectives" for protecting long-term health effects could be violated. Therefore, chronic health effects may be observed if one is persistently exposed to an API of 51 to 100 for a long time.

"Very High" levels (API in excess of 100) means that levels of one or more pollutant(s) is/are in the unhealthy range. The Hong Kong Environmental Protection Department provides advice to the public regarding precautionary actions to take for such levels.




Malaysia


The air quality in Malaysia is reported as the API or Air Pollution Index. 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 API, 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.


NOTES

In the context of this article about air quality:
  • ppmv = parts per million by volume = volume of pollutant gas per million volumes of ambient air

  • PM10 = particulate matter smaller than 10 μm in diameter

  • μg/m³ = micrograms per cubic metre of ambient air

  • μm = micrometre



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