- Air Quality Index
The Air Quality Index (AQI) is a standardized indicator of the
air qualityin a given location. It measures mainly ground-level ozoneand particulates (except the pollen count), but may also include sulfur dioxide, and nitrogen dioxide. Various agencies around the world measure such indices, though definitions may change between places.
United States Environmental Protection Agency(EPA) and the Meteorological Service of Canada(MSC) differ on what AQI structure and health classification is used:
Health classifications used by the EPA:
* 0-50 Good is usually green
* 51-100 Moderate is usually yellow
* 101-150 Unhealthy for sensitive groups is usually orange
* 151-200 Unhealthy is usually red
* 201-300 Very unhealthy is usually purple
* 301-500 Hazardous is usually maroon
The EPA's AQI 100 corresponds to 0.08 ppm ozone, and to other levels for other pollutants. Source: [http://airnow.gov/index.cfm?action=aqibroch.aqi#aqioz EPA]
The AQI standards in Canada are relatively more stringent. The current health classifications used by the
Meteorological Service of Canada(MSC) are as follows:
* 0-25*: Good (green)
* 26*-50: Fair (yellow)
* 51-100: Poor (orange)
* 101+: Very poor (red)
Ontario, 31 is the upper limit for good and 32 the lower limit for moderate. Zero to 15 is classified as very good, and is given the color blue.
In June 2007, the EPA proposed a slight possible tightening of the pollution standards associated with smog after an independent EPA scientific board said that the standard “needs to be substantially reduced” and that there is “no scientific justification” for retaining the current, weaker standard. [ [http://www.lungusa.org/site/apps/nl/content3.asp?c=dvLUK9O0E&b=40404&ct=3983577 Air Quality - American Lung Association site ] ]
In light of the new scientific findings, one should expect adjustments in the AQI such that pollution currently denoted as "moderate" will in the future be recognized as "unhealthy."
The AQI can worsen (go up) due to lack of dilution with fresh air. Stagnant air, often caused by an
anticycloneor temperature inversion, or other lack of winds lets air pollutionremain in a local area. On these days, the news mediamay ask the publicto carpoolor use public transport, or take other air pollution prevention measures such as teleworking.
The Air Pollution Index (API) levels for Hong Kong are related to the measured concentrations of ambient respirable suspended particulate (RSP), sulfur 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.
The United States Environment Protection Agency (USEPA) developed the
Pollutant Standards Index(PSI) to provide accurate, timely and easily understandable information about daily levels of air pollution.
It is no longer in use, having been replaced by the AQI, which is more sensitive. For example, particulate matter with an aerodynamic diameter less than 2.5
micrometres (PM2.5) is a sub index, replacing the less sensitive PM10 component of the PSI.
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
The air quality in the United States has improved dramatically over 23 years.
Air quality by country or region
Air Pollution Index
Atmospheric dispersion modeling
European emission standards
Indoor air quality
National Ambient Air Quality Standards- U.S. standards for EPA intervention
Pollutant Standards Index
* [http://airnow.gov AQI at airnow.gov] - cross-agency U.S. Government site
* [http://air.state.nm.us New Mexico Air Quality and API data] - Example of how New Mexico Environment Department publishes their Air Quality and API data.
* [http://www.msc-smc.ec.gc.ca/aq_smog/index_e.cfm AQI at Meteorological Service of Canada]
*The pollution index of the [http://www.metoffice.gov.uk/environment/aq/index.html UK Met Office]
* [http://www.doe.gov.my/index.php?option=com_content&task=view&id=188&Itemid=370&lang=en API at JAS (Malaysian Department of Environment)]
* [http://www.epd-asg.gov.hk API at Hong Kong] - Environmental Protection Department of the Government of the Hong Kong Special Administrative Region
* [http://www.sparetheair.org/data/air_quality.htm San Francisco Bay Area Spare-the-Air] - AQI explanation
* [http://haze.net.my Malaysia Air Pollution Index]
* [http://www.pcd.go.th/AirQuality/Regional/Default.cfm AQI in Thailand provinces] and [http://www.pcd.go.th/AirQuality/Bangkok/Default.cfm in Bangkok]
* [http://ownyourair.org/Quality/index.php The American Lung Association declares EPA standards fall short] .
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