The Air Quality Index (AQI) is a standardized index of the air quality in a given location, given in parts per billion. It measures mainly ground-level ozone and particulates (except the pollen count), but may also include sulphur dioxide, nitrogen dioxide. The word standard has several meanings: Classically, standard referred to a flag or banner; especially, a national or other ensign carried into battle; thus standard bearer indicates the one who bears, or carries, the standard. ... This article should be split into multiple articles accessible from a disambiguation page. ... This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Quality refers to the inherent or distinctive characteristics or properties of a person, object, process or other thing. ... This page refers to concentration in the chemical sense. ... Ozone (O3) in the troposphere, is a pollutant, a constituent of smog. ... Particulates, alternately referred to as Particulate Matter (PM), aerosols or fine particles are tiny particles of solid or liquid suspended in the air. ... Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ... The chemical compound nitrogen dioxide (NO2) is a red or orange/brown gas with a characteristic sharp, biting odor. ...

The U.S. Environmental Protection Agency and the Meteorological Service of Canada differ on what AQI categories are used. For other uses, see United States (disambiguation) and US (disambiguation). ... EPA redirects here. ... The Meteorological Service of Canada (MSC) is a Canadian government agency which provides meteorological information. ...

For the EPA, up to 50 on the AQI, the air is considered good (green), and up to 100 is considered moderate (yellow). Above that to 150 is unhealthy for some (orange), and to 200 is unhealthy for all (red). Severe smog or other air pollution can go to 300 (purple) or even 500 (maroon), though these are only under rare conditions. For the rock band named Smog, see Smog (band). ... This power plant in New Mexico releases sulfur dioxide and particulate matter into the air. ...

For the MSC, good is only to 25 and moderate (fair) to 50. Above that to 100 is poor and grater than that is very poor.

The AQI can worsen (go up) due to stagnant air, often caused by an anticyclone or temperature inversion, or other lack of winds. On these days, the news media may ask the public to carpool or use public transport, or take other measures such as teleworking. In meteorology, an anticyclone is a weather phenomenon associated with atmospheric high pressure. ... A temperature inversion is a meteorological phenomenon where air temperature increases with height. ... Wind is the quasi-horizontal movement of air (as opposed to an air current) caused by a horizontal pressure gradient force. ... NeWS, for Network extensible Window System, was a windowing system developed by Sun Microsystems in the late 1980s. ... Public is of or pertaining to the people; belonging to the people; relating to, or affecting, a nation, state, or community; opposed to private; as, the public treasury, a road or lake Public also refers to the general body of mankind, or of a nation, state, or community; the people... Carpooling is shared use of a car, in particular for commuting to work, often by people who each have a car but travel together to save costs. ... A taxi serving as a bus Public transport comprises all transport systems in which the passengers do not travel in their own vehicles. ...

External links

• AQI at EPA (http://www.epa.gov/airnow/aqi.html)
• AQI at MSC (http://www.atl.ec.gc.ca/airquality/whatis_index_e.html)