air quality index
News •
-
What is the air quality index (AQI)?
The air quality index (AQI) is a tool created by the U.S. Environmental Protection Agency (EPA) to communicate air quality and pollution levels, indicating whether it is healthy or unhealthy in a specific area. AQI values are updated every 8 or 24 hours, depending on the pollutant.
The EPA uses the National Ambient Air Quality Standards to calculate the AQI, which converts air pollutant levels into number ranges from 0 to 300+. These ranges are divided into color-coded levels, such as green, yellow, orange, red, purple, or maroon, to represent air hazard levels. An AQI over 100 triggers an air quality alert, as it poses health risks to sensitive groups like children or people with asthma.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What does the AQI measure?
The air quality index (AQI) is a tool used to communicate air quality and pollution levels, indicating whether the air is healthy or unhealthy in a specific area. It was first introduced in 1999 by the United States government. The EPA uses the AQI to track air quality for these six criteria air pollutants:
* Particulate matter
* Ground-level ozone
* Sulfur dioxide
* Nitrogen dioxide
* Carbon monoxide
* LeadThe AQI uses a color-coded scale to represent different levels of air hazard: green, yellow, orange, red, purple, and maroon. These levels are divided into number ranges from 0 to 300 or more. The higher the number, the worse the air quality.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How is the AQI number calculated?
The air quality index (AQI) is calculated using the National Ambient Air Quality Standards, a standardized rubric that measures the levels of air pollutants. The EPA reviews this rubric every five years. The AQI converts pollutant level calculations into number ranges from 0 to 300 (or higher), which are divided into color-coded categories indicating different levels of air hazard: green, yellow, orange, red, purple, or maroon. Higher numbers indicate worse air quality and greater health risks. An air quality alert is issued when the index exceeds 100, as this is the level at which sensitive groups may experience health hazards.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are the main pollutants included in the AQI?
The air quality index (AQI) reports on six major air pollutants:
* Particulate matter
* Ground-level ozone
* Sulfur dioxide
* Nitrogen dioxide
* Carbon monoxide
* LeadThe U.S. Environmental Protection Agency (EPA) established these standards to safeguard the environment and public health. The AQI uses these pollutants to show the level of air pollution and associated health risks.
6 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do different AQI levels affect people's health?
The air quality index (AQI) uses colors and numbers to show how clean or polluted the air is. It was created by the EPA to inform people about local air quality and potential health risks.
Different AQI levels and their effects:
- Green (0-50): Air quality is good with little to no risk.
- Yellow (51-100): Air quality is acceptable, but some unusually sensitive people may be at risk.
- Orange (101-150): Sensitive groups may experience health effects, but the general public is less likely to be affected.
- Red (151-200): Some of the general public may experience health effects, with more serious effects for sensitive groups.
- Purple (201-300): Health alert, with an increased risk of health effects for everyone.
- Maroon (301+): Health warning of emergency conditions, where everyone is more likely to be affected.
People with heart or lung conditions, children, older adults, and pregnant individuals are more vulnerable to air pollution. Exposure to air pollution can cause diseases and cancer.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What can communities do to improve air quality and lower the AQI?
Communities can improve air quality and lower the AQI by reducing pollutant emissions through cleaner fuels and processes. Focusing on mass transit can lower air pollution, congestion, and accidents. Effective strategies include restricting vehicle growth via taxes, encouraging high-density development, and investing in mass transit while limiting resources for automobiles. Also, commuters can opt for public transportation, bicycles, and walking.
Air pollution regulations and mitigation can limit emissions from various sources. Industries can use systems that convert harmful byproducts into less harmful substances.
5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
air quality index (AQI), an online, color-coded index created by the U.S. Environmental Protection Agency (EPA) that communicates whether the relative air quality and air pollution level in a given area is healthy or unhealthy. Maps of local AQI values are updated every 8 or 24 hours, depending on the pollutant, and provide an indication of the groups of people most likely to be affected by current air conditions. Many countries worldwide utilize the U.S. AQI standards to report local air quality.
The AQI was first released by the United States government in 1999, though the EPA had been tracking air quality since 1976. Under the 1970 Clean Air Act, the EPA regulates the air quality for the following six criteria air pollutants: particulate matter, ground-level ozone, sulfur dioxide, nitrogen dioxide, carbon monoxide, and lead. The latter, however, is excluded from the AQI, as the effects of lead poisoning are cumulative and cannot be accurately reflected in a daily reporting index such as the AQI.
The AQI is calculated by using a standardized rubric of concentrated air pollutant levels called the National Ambient Air Quality Standards. This rubric is reviewed by the EPA every five years. The AQI converts these calculations into number ranges (0–300 or more) that are then divided into color-coded levels of air hazard: green, yellow, orange, red, purple, or maroon. The higher the number and closer to maroon, the worse the air quality conditions and health risks. The EPA issues an air quality alert when pollutant concentrations are higher than 101 on the index, as this is the level at which people in sensitive groups—such as children, people with asthma, and those at risk of respiratory disease—begin to experience health hazards from poor air quality. Each level is accompanied by a description of the groups most likely to be affected and recommendations for limiting outdoor activities.
" height="20" alt="HEW Logo">
- Green: 0–50
“Air quality is satisfactory, and air pollution poses little or no risk.”
- Yellow: 51–100
“Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.”
- Orange: 101–150
“Members of sensitive groups may experience health effects. The general public is less likely to be affected.”
- Red: 151–200
“Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.”
- Purple: 201–300
“Health alert: The risk of health effects is increased for everyone.”
- Maroon: 301 and higher
“Health warning of emergency conditions: everyone is more likely to be affected.”
High levels of air pollution can be extremely harmful to health, especially that of children, teens, people with asthma and other lung diseases, those over 65, those with diabetes or cardiovascular disease, and pregnant individuals. The EPA warns that poor air quality can be dangerous even for healthy and active adults under the age of 65. Chronic exposure to air pollution carries an increased risk of chronic diseases and cancer and has been listed as a human carcinogen by the World Health Organization (WHO).