Understanding Air Quality Numbers: A Guide To Breathing Better

The Air Quality Index (AQI) is a tool used to communicate daily outdoor air quality and its associated health effects. The AQI uses a scale from 0 to 500, with higher values indicating increased levels of air pollution and health concerns. The AQI is divided into six colour-coded categories, ranging from good to hazardous air quality. These categories help individuals quickly assess the air quality in their communities and take necessary precautions to protect their health. The AQI tracks pollutants such as carbon monoxide, ozone, particulate matter, nitrogen dioxide, and sulfur dioxide. It is a valuable resource for individuals, especially those with respiratory or health conditions, to stay informed about the air quality in their area and make informed decisions regarding their activities and exposure to pollution.

Air Quality Index (AQI)

The Air Quality Index (AQI) is a tool for reporting daily air quality. It is a system used to warn the public when air pollution is dangerous. The AQI tracks six major air pollutants: ozone (smog), particle pollution (tiny particles from smoke, power plants, factories, vehicle exhaust, and other sources), carbon monoxide, nitrogen dioxide, sulfur dioxide, and particulate matter smaller than 2.5 microns (PM2.5). The AQI is measured on a scale from 0 to 500, with 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 divided into six color-coded categories, each corresponding to a range of index values: good, moderate, unhealthy for sensitive groups, unhealthy, very unhealthy, and hazardous. These categories are designed to help people quickly determine the level of air quality and take any necessary precautions to protect their health.

The AQI is established by the Environmental Protection Agency (EPA) in the United States, which measures pollution in the air and then uses the AQI to communicate this information to the public. The EPA establishes an AQI for five major air pollutants regulated by the Clean Air Act, which sets a health-based standard for an acceptable concentration level of these pollutants. The AQI is reported year-round through various channels such as newspapers, radio, television, and websites, making it easily accessible to the public.

It is important to note that the AQI values at or below 100 are generally considered satisfactory. However, when AQI values exceed 100, the air quality becomes unhealthy, first for certain sensitive groups of people and then for everyone as the values increase further. Sensitive groups may include children, the elderly, people with asthma or other lung diseases, individuals with cardiovascular disease, and pregnant women. Therefore, staying informed about the AQI in your area can help you take appropriate measures to protect yourself and your loved ones from the potential health risks associated with poor air quality.

Additionally, the AQI provides specific guidelines for different levels of air quality. For example, on "code orange" days, which indicate unhealthy air quality, individuals are advised to avoid prolonged periods of outdoor activity, especially in high-traffic areas. On the worst air quality days, indicated by purple or maroon, everyone is advised to stay indoors as much as possible to minimize exposure to harmful pollutants.

How to protect yourself from poor air quality

The Air Quality Index (AQI) is a system used to warn the public about dangerous levels of air pollution. The AQI uses a scale from 0 to 500, with each value representing the concentration of pollutants in the air. The higher the AQI value, the greater the level of air pollution and the more serious the health concern. For example, an AQI value of 50 or below represents good air quality, while a value over 300 indicates hazardous air quality. The AQI is divided into six colour-coded categories, ranging from green (good air quality) to maroon (extremely poor air quality).

• Check the AQI regularly: Stay informed about the current air quality in your area by checking the AQI on a daily basis. You can find this information on local news channels, newspapers, or websites.
• Reduce outdoor activities: On days with poor air quality, limit your time spent outdoors and reduce the intensity of any physical activities. Avoid exercising near high-traffic areas, as vehicle emissions can significantly contribute to air pollution.
• Protect yourself outdoors: If you must go outside during periods of poor air quality, consider wearing a mask to protect yourself from inhaling smoke particles. An N95 mask approved by the National Institute for Occupational Safety and Health (NIOSH) is recommended. Cloth or surgical masks may not effectively filter out fine particles.
• Improve indoor air quality: Take steps to ensure the air you breathe indoors is clean. Keep windows closed and use the "re-circulate" setting on your air conditioning or heating system. Avoid cooking activities that can increase indoor air pollution, such as frying or grilling.
• Support clean air initiatives: Get involved in efforts to improve air quality and reduce pollution. This can include supporting national, state, and local initiatives, as well as making personal choices to reduce your energy consumption and use alternative modes of transportation.
• Protect vulnerable individuals: Children, the elderly, pregnant women, and individuals with pre-existing health conditions are especially vulnerable to the effects of poor air quality. Take extra precautions to limit their exposure to air pollution and follow any recommendations provided by healthcare professionals.

How to find your local AQI

The Air Quality Index (AQI) is a system used to warn the public about dangerous levels of air pollution. The AQI tracks six categories of pollutants, including ozone (smog) and particle pollution (from sources like smoke, power plants, factories, and vehicle exhaust). The higher the AQI value, the greater the level of air pollution and the greater the health concern.

• Visit AirNow.gov, which provides an interactive map with data for air quality monitors in the U.S., Canada, and Mexico. You can select tabs for current, forecast, loops, or archive data, and use the drop-down panels to select specific layers and geographic outlines. The map includes colour-coded dots representing cities or reporting areas, which you can click on to see forecast information for separate pollutants.
• Check your local radio, TV weather reports, newspapers, or weather apps on your phone. These sources typically report AQI levels year-round, and you can find information about the daily air quality index for your area wherever you usually get your weather forecast.
• Use the AirNow mobile app, which provides geographic and location-based searches to help you find your local AQI.
• Visit websites like waqi.info, which provide an interactive map with flags indicating specific cities. By clicking on a flag, you can access the historical data for that location.
• Follow EnviroFlash emails, which provide updates on air quality.

How AQI values are calculated

The Air Quality Index (AQI) is calculated by converting measured pollutant concentrations to a uniform index based on the health effects associated with a pollutant. The AQI was developed by the Environmental Protection Agency (EPA) to provide a simple, uniform way to report daily air quality conditions. The EPA established National Ambient Air Quality Standards (NAAQS) for each pollutant to protect public health.

An AQI value of 100 generally corresponds to the level of the NAAQS for the pollutant. The Clean Air Act requires the EPA to review these standards every five years to reflect evolving health effects information. The Air Quality Index is adjusted periodically to reflect these changes. 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.

The AQI is divided into six categories, each with a specific colour. Each category corresponds to a different level of health concern. An AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality. When the forecast is for AQI values to be near or to exceed 101, an air quality alert is issued, as this indicates that air quality is unhealthy for certain sensitive groups of people and may be harmful to those who are sensitive to air pollution.

The final AQI value can be calculated either per hour or per 24 hours and is the maximum of six scores. The score for each pollutant is non-linear, as is the final AQI score. An individual score (Individual Air Quality Index, IAQI) is calculated using breakpoint concentrations and the same piecewise linear function to calculate intermediate values as the US AQI scale.

How AQI values are communicated

The Air Quality Index (AQI) is a tool for reporting daily air quality. It is a system used to warn the public when air pollution is dangerous. The AQI tracks ozone (smog) and particle pollution (from smoke, power plants, factories, vehicle exhaust, etc.), as well as four other widespread air pollutants. The AQI uses colours, numbers and words to communicate air quality to the public.

The AQI is divided into six colour-coded categories, each corresponding to a range of index values. The colours, from best to worst, are green, yellow, orange, red, purple and maroon. Maroon is the worst possible air quality and is rarely seen. Each category also has a specific health warning. When AQI values are at or below 100, the air quality is generally thought of as satisfactory. When AQI values are above 100, the air quality is considered unhealthy for certain sensitive groups of people, and then for everyone as values get higher. An AQI value over 300 represents hazardous air quality.

The AQI is reported by the EPA and State environmental agencies. The public can access AQI data through newspapers, radio, television, and websites. The EPA also provides year-round AQI forecasts, including maps that show how pollution levels change and move throughout the day. The AirNow.gov website and app also provide AQI data.

Frequently asked questions