Understanding The Air Quality Index: What It Means And Why It Matters

The Air Quality Index (AQI) is a tool used by government agencies to communicate to the public about the current and forecasted level of air pollution and its associated health risks. It is designed to be easy for the general public to understand, with colour-coded categories indicating the level of air pollution and the potential health concerns. The AQI takes into account various pollutants, including ozone (smog) and particle pollution, and provides a single-scale value to indicate overall air quality. Different countries have their own AQIs, and within countries, the index is updated frequently to reflect real-time changes in pollution levels.

How is the AQI calculated?

The Air Quality Index (AQI) is a tool used by government agencies to communicate to the public 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 health benchmarks used for calculating the AQI are pollutant-specific and established by the Environmental Protection Agency (EPA) through the National Ambient Air Quality Standards. The Clean Air Act requires the EPA to review these standards every five years.

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 associated health concerns. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 indicates hazardous air quality. When the AQI is above 100, the air quality is considered unhealthy for certain sensitive groups of people, and as the AQI value increases, it becomes unhealthy for everyone.

The pollutant with the highest AQI value at a given time determines the overall AQI for that hour. AQI forecasts are influenced by factors such as temperature, precipitation, wind, and cloud cover, which affect the creation and transport of pollution. Certain pollutants like carbon monoxide, sulfur dioxide, and nitrogen dioxide rarely influence the AQI and are only measured at a few sites.

The initial iteration of the AQI used standardized ambient pollutant concentrations to generate individual pollutant indices, which were then weighted and summed to form a single total air quality index. The concentrations were converted into a standard statistical distribution with a preset mean and standard deviation. While the methodology was designed to be robust, its practical application in all metropolitan areas proved challenging due to data availability and inconsistencies in monitoring methods.

What are the AQI categories?

The Air Quality Index (AQI) is a tool used by government agencies to communicate to the public about outdoor air quality and health. The AQI is divided into six categories, each corresponding to a different level of health concern. Each category has a specific colour, making it easy for people to quickly determine whether the air quality is reaching unhealthy levels in their communities. The six levels of health concern and what they mean are:

• "Good" AQI is 0-50. Air quality is considered satisfactory, and air pollution poses little or no risk.
• "Moderate" AQI is 51-100. Air quality is acceptable, however, for some pollutants, there may be a moderate health concern for a very small number of people. For example, people unusually sensitive to ozone may experience respiratory symptoms.
• "Unhealthy for sensitive groups" AQI is 101-150. Some members of the public may experience health effects, but the general public is unlikely to be affected. People with lung disease, older adults, and children are at a greater risk of health effects from exposure to pollutants.
• "Unhealthy" AQI is 151-200. Everyone may begin to experience health effects, and members of sensitive groups may experience more serious health effects.
• "Very Unhealthy" AQI is 201-300. Health warnings of emergency conditions are issued, and everyone may experience more serious health effects.
• "Hazardous" AQI is 300+. Health alerts are issued, and everyone may experience more serious health effects.

It is worth noting that the AQI varies across different countries, with different national air quality standards.

How does the AQI impact health?

The Air Quality Index (AQI) is a tool used to communicate about outdoor air quality and health. It was developed by government agencies to measure the quality of the air and inform the public about the level of air pollution. The AQI value rises with an increase in air pollution. An AQI value of 50 or below represents good air quality, while a value over 300 indicates hazardous air quality. The higher the AQI value, the greater the health concern.

The AQI is divided into six color-coded categories, each indicating a different level of health concern. When the AQI value for particle pollution is between 101 and 150, or Code Orange, the air quality is deemed "'unhealthy for sensitive groups.'" People with heart or lung disease, older adults, children, people with diabetes, and those of lower socioeconomic status are advised to reduce prolonged or heavy physical exertion. As the AQI value surpasses 150, the air quality becomes unhealthy for the entire population, with higher values posing greater health risks.

The impact of air pollution on health can vary depending on factors such as the concentration and duration of exposure, individual susceptibility, and other variables. Prolonged exposure to elevated levels of particulate matter and other pollutants can lead to irritation and inflammation of the respiratory system, causing chronic coughing, wheezing, and throat discomfort. Continuous exposure can result in reduced lung function, exacerbating symptoms for individuals with pre-existing respiratory conditions like asthma or chronic obstructive pulmonary disease (COPD).

Additionally, air pollution increases the risk of respiratory infections, heart disease, stroke, and lung cancer. Fine particulate matter, carbon monoxide, ozone, nitrogen dioxide, and sulfur dioxide are among the pollutants of significant public health concern. These pollutants can enter the bloodstream, causing systemic inflammation and damage to tissues and cells throughout the body. Exposure to air pollution during pregnancy has also been linked to adverse birth outcomes, and there is emerging evidence suggesting impacts on diabetes and neurological development in children.

To protect their health, individuals can utilize resources such as the AirNow App or EnviroFlash notifications to stay informed about real-time air quality information and take appropriate measures when the AQI reaches unhealthy levels.

How to protect yourself from poor air quality

The Air Quality Index (AQI) is a tool used by government agencies to communicate to the public about the current and forecasted level of outdoor air quality and its associated health risks. The AQI is a rating system that reflects the concentration of pollutants in the air, with a higher AQI value indicating greater air pollution and health concerns.

Stay Informed:

Keep yourself updated on the AQI in your area through daily air pollution forecasts. Sources like local radio, TV weather reports, newspapers, and websites such as airnow.gov provide color-coded AQI information. When the AQI is high, indicating unhealthy air quality, it is recommended to limit your time outdoors and reduce physical activity, especially for children and individuals with respiratory or cardiovascular issues.

Protect Yourself Outdoors:

If you must go outside when the air quality is poor, consider wearing a protective mask like an N95 respirator. Avoid areas with high traffic, as vehicle emissions can significantly contribute to air pollution.

Improve Indoor Air Quality:

Maintain good indoor air quality by keeping windows closed and using the ""re-circulate" setting on your air conditioning or heating system. Avoid activities that can increase indoor air pollution, such as cooking, especially frying or grilling. Refrain from smoking, using fireplaces, or lighting candles or incense.

Reduce Energy Consumption:

Lower your energy use at home, as generating electricity creates air pollution. Use energy-efficient appliances, and consider alternative transportation methods like walking, biking, or using public transport instead of driving.

Support Clean Air Initiatives:

Get involved in initiatives that advocate for cleaner air, such as the Healthy Air Campaign. Support national, state, and local efforts to address and reduce pollution sources. Your actions can help improve air quality and protect the health of yourself and those around you.

AQI in the US vs. the EU

The Air Quality Index (AQI) is an indicator developed by government agencies to communicate to the public about current and forecasted air pollution levels. The AQI is computed using an air pollutant concentration over a specified averaging period, obtained from an air monitor or model. The higher the AQI, the greater the level of air pollution and the associated public health risk. As a result, when the AQI is high, governmental bodies typically advise vulnerable groups to reduce physical activity outdoors or even avoid going outside altogether.

In the United States, the AQI is the Environmental Protection Agency's (EPA) tool for communicating about outdoor air quality and health. The US AQI has six color-coded categories, each representing a range of index values. For instance, an AQI value of 50 or below represents good air quality, while a value over 300 indicates hazardous air quality. The EPA also establishes an AQI for five major air pollutants regulated by the Clean Air Act, with national air quality standards set to protect public health.

In the European Union, there is the EU-supported project CiteairII, which has developed the Common Air Quality Index (CAQI). The CAQI is a number on a scale from 0 to 100, where lower values indicate good air quality and higher values mean extremely poor air quality. The main goal of the CAQI is to attract attention to urban air pollution, particularly from traffic, and help people reduce their exposure. The CAQI is intended to encourage comparisons across the EU without replacing local indices. Additionally, the Year Average Common Air Quality Index (YACAQI) is defined, where different pollutant sub-indices are normalised to a value near unity.

While both the US and the EU have made significant improvements in air quality, there is a recognised need for a more integrated and ambitious approach to air quality management in both regions.

Frequently asked questions