Air Quality Index, 2016
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The Air Quality Index (AQI) is a value used primarily by governments in reporting daily air quality for states, regions, metropolitan areas, as well as nationwide air quality. In the United States, the higher the value, the higher the level of one or more of the five air pollutants regulated under the Clean Air Act. Additionally, a higher AQI generally corresponds to a higher percentage of the population that may experience negative health effects within hours or days of breathing outside air. The AQI in the United States is administered by the Environmental Protection Agency and measured by monitoring networks run by state and local air quality agencies.
The AQI includes five air pollutants in the United States: ground-level ozone (commonly known as smog), particulate matter (a mix of solid and liquid particles suspended in the air), carbon monoxide (a colorless, odorless poisonous gas produced when fuel is burned in cars, trucks, small engines, stoves, lanterns, grills, fireplaces, or furnaces), sulfur dioxide (a toxic gas formed by burning sulfur during industrial activity and contributes to acid rain), and nitrogen dioxide (a brown-reddish gas used to manufacture sulfuric and nitric acids). Each of these pollutants is regulated through national air quality standards established by the EPA. Daily and historical AQI values can be found on the website AirNow.gov.[1][2]
Background
According to the Code of Federal Regulations (CFR), the Air Quality Index (AQI) "is a tool that simplifies reporting air quality to the general public." The AQI converts the levels of five air pollutants through mathematical formulas into a single index. The scale of the index is then divided into six categories, each of which is associated a health message about the potential negative effects of air quality conditions at a particular level. According to the CFR, the AQI's advantages include the following:[3]
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a. It is simple to create and understand. |
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| —Code of Federal Regulations[3] | ||
The federal Clean Air Act requires each state to have air monitoring stations for the five air pollutants included in the AQI. These monitoring networks, known as State and Local Monitoring Stations (SLAMS), provide air quality results from a variety of air monitors in different areas. To learn more about air monitoring networks, click here.[3]
AQI measurement
The AQI is measured on a 0-500 scale. An AQI of 100 coincides with the short-term national air quality standard set by the EPA for each pollutant (measured during a period of 24 hours or less). The higher the AQI number, the higher the concentration of the pollutant(s) thus potentially the more negative health concerns associated with those pollutants. Though each pollutant has a different standard and is found in the air at different levels, the EPA standardizes the AQI so that a particular range of numbers means the same for each pollutant.[1][2]
According to the EPA, the AQI is typically below 100 for many U.S. communities. Though larger cities may see their AQI exceed 100 more often, they generally have higher pollutant levels than smaller cities due primarily to higher populations, more vehicles on the road, and sometimes more industrial activities. Moreover, an AQI of 200 or above occurs infrequently according to the EPA, while an AQI above 300 occurs very rarely since AQI values generally rise to such levels due to forest fires and similar events.[1][2]
Additionally, the AQI fluctuates between seasons and throughout the day. For example, carbon monoxide levels in some areas are sometimes higher during winter because cold weather can hamper the carbon monoxide control systems in cars and trucks. Ground-level ozone is sometimes higher in warm weather because ozone forms more quickly with more heat and sunlight. AQI levels also fluctuate during the day. For example, ozone levels may rise in the afternoon given generally warmer temperatures during that time, while carbon monoxide levels can rise during mornings and evenings because more cars and trucks are on the road, particularly in highly populated cities.[1][2]
AQI ranges
The AQI ranges listed below correspond to different levels for the five air pollutants listed above. These levels are converted by mathematical formulas into an AQI value.[1][2]
| Air Quality Index by numerical value, air quality conditions, and description | ||
|---|---|---|
| Numerical value (0-500) | Air quality conditions | Description |
| 0 to 50 | Good | Air quality within this range is considered satisfactory; air pollution at this level poses little to no risk. |
| 51 to 100 | Moderate | This range is considered healthy for the vast majority of people. However, for higher levels of ground-level ozone, some particularly sensitive individuals may experience moderate health issues, such as coughing or sore throat. |
| 101 to 150 | Unhealthy for sensitive groups | Sensitive groups, which are defined below, may experience health issues related to ozone exposure, and individuals with heart or lung disease may react negatively to higher levels of particulate matter. The general public, however, is not likely to be affected within this range. |
| 151 to 200 | Unhealthy | The EPA considers the general public to be at risk within this range. Individuals may experience shortness of breath, fatigue, and chest pain after prolonged exposure to outdoor air. Sensitive groups may experience more severe health effects. |
| 201 to 300 | Very unhealthy | Though infrequent, this range warrants a health alert by the EPA, and the entire population may experience serious health effects. |
| 301 to 500 | Hazardous | Though considered very rare by the EPA, this range indicates that air quality has reached emergency conditions. The entire population is considered more likely than not to experience serious health effects. |
| Source: U.S. Environmental Protection Agency, "Air Quality Index (AQI)," | ||
Definition of sensitive groups
While more people will generally experience more negative health effects when pollutant levels are very high (defined as an AQL of 201 or higher), the EPA categorizes certain individuals as part of sensitive groups, which may be more likely to experience negative health effects as pollutant levels rise above an AQL of 100. The EPA considers ground-level ozone and particulate matter to be of particular concern to these groups. However, the health effects of these pollutants can vary widely among individuals, and different times of the day may experience different levels of these pollutants.[2]
Individuals with asthma, chronic bronchitis, emphysema, or other lung problems are particularly sensitive to higher ground-level ozone levels. These individuals can also include children and older adults with asthma or lung issues. Meanwhile, others may be more sensitive to ozone due to genetic factors, while some individuals who do prolonged and rigorous exercise or work outdoors may breathe in more ozone as ozone levels rise. Similarly, individuals with heart or lung problems (such a heart failure, coronary artery disease, asthma, or chronic obstructive pulmonary disease) are particularly sensitive to higher particulate matter levels. These individuals can also include older adults or children with similar health issues.[2]
When an AQI for a pollutant is over 100, federal regulations require state and local air quality agencies to report that the following sensitive groups may be affected.[3]
| Reporting for groups affected by AQI levels above 100 for each pollutant | |
|---|---|
| Pollutant | Groups |
| Ground-level ozone | Children and people with asthma |
| Particulate matter 2.5 | People with respiratory or heart disease, including older adults and children |
| Particulate matter 10 | People with respiratory disease |
| Carbon monoxide | People with heart disease |
| Sulfur dioxide (SO2 | People with asthma |
| Nitrogen dioxide (NO2 | Children and people with respiratory disease |
| |Source: Code of Federal Regulations, "40 CFR Part 58, Appendix G to Part 58 - Uniform Air Quality Index (AQI) and Daily Reporting" | |
AQI reporting
Federal regulations specify how state and/or delegated local air quality agencies must report the AQI. For example, all metropolitan areas with a population over 350,000 must report the AQI at least five days a week (exceptions to this requirement can be found here. An AQI report must include the metropolitan area(s) or subdivisions being monitored, the day on which the AQI is being reported, the pollutant most responsible for the highest AQI reported during the day, the highest AQI value reported during the day, and the description associated with the AQI value (as listed in the table with AQI ranges found above). Because AQI calculations occur over a 24-hour period, state and local agencies are in effect reporting the AQI for the previous day. Additionally, state and local air quality agencies must make the AQI report publicly available, while the EPA encourages reporting the AQI in as many ways as possible. This can include television, newspapers, radio, recorded phone messages, faxes, websites, widgets, apps, and social media.[1][2][3]
See also
External links
Footnotes
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 U.S. Environmental Protection Agency, "Technical Assistance Document for the Reporting of Daily Air Quality – the Air Quality Index (AQI)," May 2016
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 U.S. Environmental Protection Agency, "Air Quality Index: A Guide to Air Quality and Your Health," accessed December 14, 2016
- ↑ 3.0 3.1 3.2 3.3 3.4 Code of Federal Regulations, "40 CFR Part 58, Appendix G to Part 58 - Uniform Air Quality Index (AQI) and Daily Reporting," accessed December 13, 2016
- ↑ Note: This text is quoted verbatim from the original source. Any inconsistencies are attributable to the original source.
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