User:Milton Beychok/Sandbox

The Air Quality Index (AQI) (also known as the Air Pollution Index (API) or Pollutant Standard Index (PSI)) is a number used by government agencies to characterize the quality of the air at a given location. As the AQI increases, an increasingly large percentage of the population is likely to experience increasingly severe adverse health effects.

To compute the AQI requires an air pollutant concentration from a monitor or model. The function used to convert from air pollutant concentration to AQI varies by pollutant, and is different in different countries.

In many countries, air quality index values are divided into ranges, and each range is assiged a descriptor and a color code. Standardized public health advisories are associated with each AQI range. An agency might also encourage members of the public to take public transportation or work from home when AQI levels are high.

Most air contaminants do not have an associated AQI. Many countries monitor ground-level ozone, particulates, sulfur dioxide, carbon monoxide and nitrogen dioxide and calculate air quality indices for these pollutants.

Air Quality Indices by country

Canada's AQHI Air Quality Health Index (AQI) Health Risk Category Color Code 1 – 3 Low 4 – 6 Moderate 7 – 10 High 10+ Very High

Canada

Environment Canada, the national environmental protection agency of Canada, uses Air Quality Health Index (AQHI) categories ranging from 1 to 10+ and each category has an assigned color code (see adjacent table) that enables members of the general public to easily identify their health risks as indicated in published air quality forecasts.

As shown in the adjacent table:

• The three AQHI levels of 1, 2 and 3 are all in the low risk category.
• The three AQHI levels of 4, 5 and 6 are all in the moderate risk category.
• The four AQHI levels of 7, 8, 9 and 10 are all in the high risk category.
• The AQHI level of 10+ is the very high risk category.

As of 2009, many of the Canadian provinces, if not all, have adopted the AQHI categories implemented by Environment Canada.

Hong Kong's API Air Pollution Index (API) Health Effect Category Color Code 0 – 25 Low   26 – 50 Medium   51 – 100 High   101 – 200 Very High   201 – 500 Severe

Hong Kong

The Hong Kong Environmental Protection Department (Hong Kong EPD) has developed an Air Pollution Index (API) based upon 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.

Hong Kong's Air Pollution Index (AQHI) scale ranges from 0 to 500 corresponding to adverse health effects that range from low to severe as shown in the adjacent chart:

• An API 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.

• Persistent high API values (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.

• API values in excess of 100 (very high) mean that levels of one or more pollutant(s) is/are in the unhealthy range. The Hong Kong EPD provides advice to the public regarding precautionary actions to take for such levels.

China's National API Air Pollution Index (API) Air Quality Category 0 – 50 Excellent 51 – 100 Good 101 – 200 Slightly polluted 201 – 300 Moderately polluted 301+ Heavily polluted

China

China's Ministry of Environmental Protection (SEPA) for the conversion of AQI values to concentration values and for the reverse conversion of concentrations to AQI values.

A national map of the United States containing daily AQI forecasts across the nation, developed jointly by the U.S. EPA and NOAA is also available online.

The Clean Air Act of 1990 requires the U.S. EPA to review its National Ambient Air Quality Standards every five years to reflect evolving health effects information. The Air Quality Index is adjusted periodically to reflect these changes.

Air pollutant concentration measurement units

In the United States, the concentrations of the air pollutants involved in the AQI are usually expressed as:

• Ozone and sulfur dioxides: ppbv = parts per billion (10 ⁹) by volume = volume of pollutant gas per billion volumes of ambient air
• Carbon monoxide: ppmv = parts per million (10 ⁶) by volume = volume of pollutant gas per million volumes of ambient air
• PM₁₀, defined as particulate matter having an aerodynamic diameter of 10 μm (micrometer) or less: ug/m³ = micrograms of particulate matter per cubic metre of ambient air
• PM_2.5, defined as particulate matter having an aerodynamic diameter of 2.5 μm (micrometer) or less: ug/m³ = micrograms of particulate matter per cubic metre of ambient air

References

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See also

• Air pollution

• Atmospheric dispersion modeling
• Emission standard
• European emission standards
• Smog
• U.S. National Ambient Air Quality Standards

External links

• AQI at airnow.gov - cross-agency U.S. Government site
• New Mexico Air Quality and API data - Example of how New Mexico Environment Department publishes their Air Quality and API data.
• AQI at Meteorological Service of Canada
• The UK Air Quality Archive
• The pollution index of the UK Met Office
• API at JAS (Malaysian Department of Environment)
• API at Hong Kong - Environmental Protection Department of the Government of the Hong Kong Special Administrative Region
• San Francisco Bay Area Spare-the-Air - AQI explanation
• Malaysia Air Pollution Index
• AQI in Thailand provinces and in Bangkok
• The American Lung Association declares EPA standards fall short.