Air Quality Index - AbsoluteAstronomy.com

Air quality is defined as a measure of the condition of air relative to the requirements of one or more biotic species or to any human need or purpose. Air quality indices (AQI) are numbers 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.
Air quality index values are divided into ranges, and each range is assigned 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.

Limitations of the AQI

Most air contaminants do not have an associated AQI. Many countries monitor ground-level ozone, particulates, sulfur dioxide

Sulfur dioxide

Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...

, carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

and nitrogen dioxide

Nitrogen dioxide

Nitrogen dioxide is the chemical compound with the formula it is one of several nitrogen oxides. is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year. This reddish-brown toxic gas has a characteristic sharp, biting odor and is a prominent...

and calculate air quality indices for these pollutants.

Causes of poor air quality

The AQI can worsen (go up) due to lack of dilution of air emissions by fresh air. Stagnant air, often caused by an anticyclone

Anticyclone

An anticyclone is a weather phenomenon defined by the United States' National Weather Service's glossary as "[a] large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in the Northern Hemisphere, counterclockwise in the Southern Hemisphere"...

or temperature inversion, or other lack of wind

Wind

Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...

s lets air pollution

Air pollution

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....

remain in a local area.

Canada

Air quality in Canada has been reported for many years with provincial Air Quality Indices (AQIs). Significantly, AQI values reflect air quality management objectives, which are based on the lowest achievable emissions rate, and not exclusively concern for human health. The Air Quality Health Index

Air Quality Health Index

The Air Quality Health Index or is a scale designed to help understand the impact of air quality on health. It is a health protection tool used to make decisions to reduce short-term exposure to air pollution by adjusting activity levels during increased levels of air pollution...

or (AQHI) is a scale designed to help understand the impact of air quality on health.
It is a health protection tool used to make decisions to reduce short-term exposure to air pollution by adjusting activity levels during increased levels of air pollution. The Air Quality Health Index also provides advice on how to improve air quality by proposing behavioral change to reduce the environmental footprint. This index pays particular attention to people who are sensitive to air pollution. It provides them with advice on how to protect their health during air quality levels associated with low, moderate, high and very high health risks.

The Air Quality Health Index provides a number from 1 to 10+ to indicate the level of health risk associated with local air quality. On occasion, when the amount of air pollution is abnormally high, the number may exceed 10. The AQHI provides a local air quality current value as well as a local air quality maximums forecast for today, tonight, and tomorrow, and provides associated health advice.

Risk:

Low (1-3)

Moderate (4-6)

High (7-10)

Very high (above 10)

Health Risk

Air Quality Health Index

"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.

API	0 - 25	Low	None expected.
26 - 50	Medium	None expected for the general population.
51 - 100	High	Acute health effects are not expected but chronic effects may be observed if one is persistently exposed to such levels.
100 - 200	Very High	People with existing heart or respiratory illnesses may notice mild aggravation of their health conditions. Generally healthy individuals may also notice some discomfort.
201 - 500	Severe	People with existing heart or respiratory illnesses may experience significant aggravation of their symptoms. There may also be widespread symptoms in the healthy population (e.g. eye irritation, wheezing, coughing, phlegm and sore throats).

Mainland China

China's Ministry of Environmental Protection (MEP

Ministry of Environmental Protection of the People's Republic of China

The Ministry of Environmental Protection of the People's Republic of China , formerly State Environmental Protection Administration , is a cabinet-level ministry in the executive branch of the Chinese Government . It replaced the SEPA during the March 2008 National People's Congress sessions in...

) is responsible for measuring the level of air pollution in China. As of 28 August 2008, MEP monitors daily pollution level in 86 of its major cities. The API level is based on the level of 5 atmospheric pollutants, namely sulfur dioxide

Sulfur dioxide

(SO₂), nitrogen dioxide

Nitrogen dioxide

(NO₂), suspended particulates (PM₁₀), carbon monoxide

Carbon monoxide

(CO), and ozone

Ozone

Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

(O₃) measured at the monitoring stations throughout each city.

API Mechanics

An individual score is assigned to the level of each pollutant and the final API is the highest of those 5 scores. The pollutants can be measured quite differently. SO₂, NO₂ and PM₁₀ concentration are measured as average per day. CO and O₃ are more harmful and are measured as average per hour. The final API value is calculated per day.

The scale for each pollutant is non-linear, as is the final API score. Thus an API of 100 does not mean twice the pollution of API at 50, nor does it mean twice as harmful. While an API of 50 from day 1 to 182 and API of 100 from day 183 to 365 does provide an annual average of 75, it does not mean the pollution is acceptable even if the benchmark of 100 is deemed safe. This is because the benchmark is a 24 hour target. The annual average must match against the annual target. It is entirely possible to have safe air every day of the year but still fail the annual pollution benchmark.

API and Health Implications (Daily Targets)

API	0 - 50	Excellent	No health implications
51 -100	Good	No health implications
101-150	Slightly Polluted	Slight irrations may occur, individuals with breathing or heart problems should reduce outdoor exercise.
151-200	Lightly Polluted	Slight irrations may occur, individuals with breathing or heart problems should reduce outdoor exercise.
201-250	Moderately Polluted	Healthy people will be noticeably affected. People with breathing or heart problems will experience reduced endurance in activities. These individuals and elders should remain indoors and restrict activities.
251-300	Heavily Polluted	Healthy people will be noticeably affected. People with breathing or heart problems will experience reduced endurance in activities. These individuals and elders should remain indoors and restrict activities.
300+	Severely Polluted	Healthy people will experience reduced endurance in activities. There may be strong irritations and symptoms and may trigger other illnesses. Elders and the sick should remain indoors and avoid exercise. Healthy individuals should avoid out door activities.

Mexico

The air quality in Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

is reported in IMECAs. The IMECA is calculated using the measurements of average times of the chemicals ozone

Ozone

Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...

(O₃), sulphur dioxide (SO₂), nitrogen dioxide

Nitrogen dioxide

(NO₂), carbon monoxide

Carbon monoxide

(CO) and particles lower than 10 micrometers (PM₁₀).

Singapore

Singapore , officially the Republic of Singapore, is a Southeast Asian city-state off the southern tip of the Malay Peninsula, north of the equator. An island country made up of 63 islands, it is separated from Malaysia by the Straits of Johor to its north and from Indonesia's Riau Islands by the...

uses the Pollutant Standards Index

Pollutant Standards Index

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 to provide a way for broadcasts and newspapers to report air quality on a daily basis.The...

to report on its air quality.
The PSI chart below is grouped by index values and descriptors, according to the National Environment Agency

National Environment Agency

National Environment Agency formed on 1 July 2002, is a statutory board under the Ministry of the Environment and Water Resources in Singapore. As a statutory board, it gives NEA greater administrative autonomy to be more nimble in the protection of the environment...

PSI
CAI	Description	Health Implications
0-50	Good	A level that will not impact patients suffering from diseases related to air pollution.
51-100	Moderate	A level that may have a meager impact on patients in case of chronic exposure.
101-150	Unhealthy for sensitive groups	A level that may have harmful impacts on patients and members of sensitive groups.
151-250	Unhealthy	A level that may have harmful impacts on patients and members of sensitive groups (children, aged or weak people), and also cause the general public unpleasant feelings.
251-350	Very unhealthy	A level that may have a serious impact on patients and members of sensitive groups in case of acute exposure.
351-500	Hazardous	A level that may need to take emergency measures for patients and members of sensitive groups and have harmful impacts on the general public.

United Kingdom

AEA Technology

AEA Technology plc was formed in 1996 as the privatised offshoot of the United Kingdom Atomic Energy Authority. It is a constituent of the FTSE Fledgling Index. Originally it consisted of divisions with expertise in a wide variety of areas, mostly the products of nuclear-related research...

issue air quality forecasts for the UK on behalf of DEFRA 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.

Index	1 - 3	Low	Effects are unlikely to be noticed even by individuals who know they are sensitive to air pollutants.
4 - 6	Moderate	Mild effects, unlikely to require action, may be noticed amongst sensitive individuals.
7 - 9	High	Significant effects may be noticed by sensitive individuals and action to avoid or reduce these effects may be needed (e.g. reducing exposure by spending less time in polluted areas outdoors). Asthmatics will find that their 'reliever' inhaler is likely to reverse the effects on the lung.
10	Very High	The effects on sensitive individuals described for 'High' levels of pollution may worsen.

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

Pollutant	Health Effects at High Level
Nitrogen dioxide Ozone Sulphur dioxide	These gases irritate the airways of the lungs, increasing the symptoms of those suffering from lung diseases.
Particulates	Fine particles can be carried deep into the lungs where they can cause inflammation and a worsening of heart and lung diseases

United States

The United States Environmental Protection Agency

United States Environmental Protection Agency

The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...

(EPA) uses the following AQI:

Air Quality Index (AQI) Values	span style="color:#fff; font-family:arial; font-size:1em;">Levels of Health Concern	span style="color:#fff; font-family:arial; font-size:1em;">Colors
0 to 50	Good	Green
51 to 100	Moderate	Yellow
101 to 150	Unhealthy for Sensitive Groups	Orange
151 to 200	Unhealthy	Red
201 to 300	Very Unhealthy	Purple
301 to 500	Hazardous	Maroon

PM_2.5 24-Hour AQI Loop, Courtesy US EPA

The air quality index is a piecewise linear function of the pollutant concentration.
At the boundary between AQI categories, there is a discontinuous jump of one AQI unit.
To convert from concentration to AQI the equation:

is used, where:

= the (Air Quality) index,

= the pollutant concentration,

= the concentration breakpoint that is ≤

= the concentration breakpoint that is ≥

= the index breakpoint corresponding to

.

For breakpoints for different pollutants, see:
http://www.epa.gov/airnow/aqi_tech_assistance.pdf.

For example, suppose a monitor records a 24-hour average fine particle (PM_2.5) concentration of 12.0 micrograms per cubic meter. EPA's table of breakpoints for PM_2.5 is:

				Category
0	15.4	0	50	Good
15.5	40.4	51	100	Moderate
40.5	65.4	101	150	Unhealthy for Sensitive Groups
65.5	150.4	151	200	Unhealthy
150.5	250.4	201	300	Very Unhealthy
250.5	350.4	301	400	Hazardous
350.5	500.4	401	500	Hazardous

The equation above results in an AQI of:

,
corresponding to air quality in the "Good" range.

If multiple pollutants are measured at a monitoring site, then the largest or "dominant" AQI value is reported for the location.

To convert an air pollutant concentration to an AQI, EPA has developed a calculator:
http://airnow.gov/index.cfm?action=aqi.conc_aqi_calc.
To convert an air quality index to an air pollutant concentration, see:
http://airnow.gov/index.cfm?action=aqi.aqi_conc_calc.

Current ambient monitoring data and forecasts of air quality that are color-coded in terms of the air quality index are available at: http://www.airnow.gov/.

The Clean Air Act (USA) (1990) requires EPA to review its National Ambient Air Quality Standards

National Ambient Air Quality Standards

The National Ambient Air Quality Standards are standards established by the United States Environmental Protection Agency under authority of the Clean Air Act that apply for outdoor air throughout the country...

every five years to reflect evolving health effects information. The Air Quality Index is adjusted periodically to reflect these changes.

Abbreviations in this article

In the context of this article about air quality:

ppbv=parts per billion by volume = a portion anomaly volume of pollutant gas per billion volumes of ambient air
ppmv = parts per million by volume = volume of pollutant gas per million volumes of ambient air
PM_2.5 = particulate matter smaller than 2.5 μm in aerodynamic diameter
Aerodynamic diameter
Aerodynamic diameter is a physical property of a particle in a viscous fluid such as air. In general, particles have irregular shapes with actual geometric diameters that are difficult to measure. Aerodynamic diameter is an expression of a particle's aerodynamic behavior as if it were a perfect...
PM₁₀ = particulate matter smaller than 10 μm in aerodynamic diameter
μg/m³ = micrograms per cubic metre of ambient air
μm = micrometre

Air quality by country or region

British Columbia
Air pollution in British Columbia
Air pollution is a concern in British Columbia, Canada because of its effects on health and visibility. Air quality is influenced in British Columbia by numerous mountain ranges and valleys, which complicate atmospheric pollution dispersion and can lead to high concentrations of pollutants such as...

Hong Kong
Air pollution in Hong Kong
Air pollution in Hong Kong is considered a serious problem. Visibility is currently less than eight kilometres for 30% of the year. Cases of asthma and bronchial infections have soared in recent years due to reduced air quality....

External links

CAI at Airkorea.or.kr - website of South Korea Environmental Management Corp.
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.

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Limitations of the AQI

Causes of poor air quality

Canada

Mainland China

Mexico

Singapore

United Kingdom

United States

Abbreviations in this article

Air quality by country or region

See also

External links