Greta Jimenez
The Air Quality Index (AQI) is a tool used to communicate about outdoor air quality and health. It was developed by the US Environmental Protection Agency (EPA) to provide a simple, uniform way to report daily air quality conditions. The AQI is calculated by converting measured pollutant concentrations to a uniform index based on the health effects associated with a pollutant. The AQI includes six color-coded categories, each corresponding to a range of index values. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality. The AQI is an important tool for warning the public about dangerous levels of air pollution and helping people take steps to protect their health.
| Characteristics | Values |
|---|---|
| Purpose | To communicate about outdoor air quality and health |
| Pollutants measured | Ozone, particulates, sulfur dioxide, carbon monoxide, nitrogen dioxide, etc. |
| Scale | 0–500 |
| Categories | Six |
| Descriptor | Yes |
| Color code | Yes |
| Health advisory | Yes |
| Calculation | Measured pollutant concentrations are converted to a uniform index based on health effects |
| Benchmarks | Pollutant-specific, established by the EPA through the National Ambient Air Quality Standards |
| Review frequency | Every five years |
| Alert | Issued when AQI exceeds 100 |
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What You'll Learn
The Air Quality Index (AQI)
The AQI is typically presented as a scale that runs from 0 to 500, with each point on the scale corresponding to a specific level of air pollution and associated health concerns. The higher the AQI value, the greater the level of air pollution and the more significant the potential health risks. For example, an AQI value of 50 or below generally indicates good air quality, while a value over 300 suggests hazardous air quality.
The AQI is divided into six color-coded categories, each representing a range of index values. These categories are assigned specific colors to make it easier for people to quickly assess the air quality in their communities. Each category also comes with health advice, providing guidance on how to protect oneself during different levels of air quality. The six categories are:
- Good: AQI value of 50 or below, indicating good air quality.
- Moderate: AQI values between 51 and 100, indicating satisfactory air quality for most individuals.
- Unhealthy for Sensitive Groups: AQI values between 101 and 150, indicating that certain sensitive groups, such as people with respiratory conditions, may experience health effects.
- Unhealthy: AQI values between 151 and 200, indicating that the air quality is unhealthy for everyone and may cause health issues for many individuals.
- Very Unhealthy: AQI values between 201 and 300, indicating that the air quality is very unhealthy, and everyone may experience more severe health effects.
- Hazardous: AQI value above 300, indicating hazardous air quality with potential severe health impacts for all individuals.
It's important to note that the AQI values and categories are based on national standards and may vary across different countries. Additionally, the AQI can be influenced by various factors, such as traffic, wildfires, and stagnant air caused by low wind speeds or temperature inversion, which can trap pollutants in a specific area.
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How AQI values are calculated
The Air Quality Index (AQI) is a tool for understanding air pollution levels and communicating about outdoor air quality and health. It is calculated based on six key pollutants: particulate matter (PM2.5 and PM10), ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen dioxide (NO2). The AQI is designed to provide a simple, uniform way to report daily air quality conditions, with each pollutant having a set of "breakpoints" or concentration ranges that correspond to different AQI values. These breakpoints allow the raw pollutant concentrations to be converted into AQI values that fall into one of six categories, from "'Good" to "Hazardous". The final AQI value can be calculated either per hour or per 24 hours and is the maximum of these six scores.
The AQI is calculated by converting measured pollutant concentrations to a uniform index based on the health effects associated with a pollutant. The health benchmarks used for calculating the AQI are pollutant-specific and are established by the Environmental Protection Agency (EPA) through the National Ambient Air Quality Standards (NAAQS). An AQI value of 100 generally corresponds to the level of the NAAQS for the pollutant, and AQI values above 100 indicate unhealthy air quality, first for certain sensitive groups of people, then for everyone as values increase. When the AQI is forecasted to be near or exceed 101, an air quality alert is typically issued, as these conditions can be harmful to those sensitive to air pollution.
To convert an air pollutant concentration to an AQI, the EPA has developed a calculator. If multiple pollutants are measured at a monitoring site, then the largest or "dominant" AQI value is reported for that location. The ozone AQI between 100 and 300 is computed by selecting the larger value between the AQI calculated with a 1-hour ozone value and the AQI computed with the 8-hour ozone value. AQI values of 301 or greater are calculated using 1-hour ozone concentrations.
It is important to note that different countries and systems may use varying averaging periods for different pollutants when calculating the AQI. For example, some systems may use 24-hour averages for particulate matter, while others rely on shorter periods for certain pollutants like ozone. Additionally, the AQI does not account for temperature or pollen levels, which may increase sensitivity to air pollutants. Weather conditions, including temperature, precipitation, wind, and cloud cover, can also affect pollution creation and transport from other areas.
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AQI categories and colours
The Air Quality Index (AQI) is a tool used by the United States Environmental Protection Agency (EPA) to communicate information about outdoor air quality and health. The AQI is divided into six colour-coded categories, each corresponding to a range of index values. Each category is assigned a specific colour, making it easy for people to quickly determine the level of health concern in their communities.
The six categories of the AQI are:
- Good: An AQI value of 50 or below represents good air quality.
- Unhealthy for sensitive groups: AQI values above 50 are considered unhealthy, initially for certain sensitive groups of people. These include children, the elderly, and individuals with respiratory or cardiovascular problems.
- Unhealthy: As AQI values continue to rise above 100, the air quality becomes unhealthy for everyone.
- Very Unhealthy: AQI values in this range indicate a more severe level of air pollution and a higher health concern.
- Hazardous: An AQI value over 300 represents hazardous air quality. At this level, governmental bodies may encourage people to avoid going outside and to use masks and air purifiers when outdoors.
- Extreme: This category indicates extremely hazardous air quality with potential emergency-level health risks.
It is important to note that the AQI values and categories can vary slightly depending on the country and their specific air quality standards. For example, Hong Kong's Air Quality Health Index (AQHI) is measured on a scale of 1 to 10+, with categories such as low, moderate, high, and very high health risks.
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AQI and health
The Air Quality Index (AQI) is a tool used to communicate about outdoor air quality and health. It is calculated based on the measurement of particulate matter (PM2.5 and PM10), Ozone (O3), Nitrogen Dioxide (NO2), Sulfur Dioxide (SO2), and Carbon Monoxide (CO) emissions. The AQI is designed to provide information about the health effects of common air pollutants and how individuals can protect themselves from these effects.
The AQI typically ranges from 0 to 500 and is divided into six color-coded categories, each indicating a different level of health concern. An AQI value of 50 or below represents good air quality, while a value over 300 indicates hazardous air quality. Values above 100 are considered unhealthy, initially for sensitive groups of people, and then for everyone as the AQI continues to increase.
When the AQI is predicted to be elevated, public health organizations may issue advisories and recommendations to protect the health of individuals, especially those who are sensitive to air pollution. These recommendations may include avoiding outdoor exertion, using masks and air purifiers, and reducing emissions by using public transportation.
During periods of extremely poor air quality, when acute exposure may pose significant health risks, emergency plans may be implemented to temporarily shut down major emitting industries until conditions improve. The AQI is an important tool for raising awareness about the impact of air pollution on health and guiding decisions to reduce short-term exposure and improve air quality.
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AQI and behaviour change
The Air Quality Index (AQI) is a tool used by the EPA to communicate about outdoor air quality and health. It is a nationally uniform, colour-coded index for reporting and forecasting daily air quality. The AQI is divided into six categories, each corresponding to a different level of health concern. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 indicates hazardous air quality.
AQI values at or below 100 are generally considered satisfactory. When AQI values are above 100, air quality is considered unhealthy, initially for certain sensitive groups of people, and then for everyone as AQI values increase. These sensitive groups include people with asthma, who are almost twice as likely to report a change in outdoor activity based on an air quality alert. The general population is also influenced by air quality alerts, with those without asthma more than three times as likely to report a change in outdoor activity.
The AQI is based on the measurement of several pollutants, including particulate matter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) emissions. Advancements in air quality monitoring can support better public communication and awareness of the AQI. For instance, the EPA's AirNow website provides forecasts, email notifications, and an app to help individuals stay informed about air quality.
Behaviour change interventions are necessary to promote awareness and empower individuals to take protective actions. Participatory strategies are particularly effective in fostering protective and mitigating behaviours. These strategies focus on empowering individuals to take actions that align with their circumstances, such as avoiding exposure to air pollution and reducing polluting activities. For example, individuals can adjust their activity levels during periods of increased air pollution, especially those sensitive to air pollution, to protect their health.
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Frequently asked questions
A pollution index is a tool used to communicate about outdoor air quality and health. It is calculated by converting measured pollutant concentrations to a uniform index based on the health effects associated with a pollutant.
The AQI is a specific type of pollution index that is used to warn the public when air pollution is dangerous. It tracks ozone (smog) and particle pollution, as well as four other widespread air pollutants. The AQI was developed by the U.S. Environmental Protection Agency (EPA) to provide a simple, uniform way to report daily air quality conditions.
The AQI is divided into six color-coded categories, each corresponding to a range of index values. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality.
