How to Understand Air Quality

Breathing polluted air can be risky. Keep track of the Air Quality Index (AQI) in your area and follow the guidelines in your area to protect yourself when air quality is unhealthy.


Aaron Baker

May 7, 2021 • Updated Mar 17, 2022 • 4 min read

Find air pollution and other environmental hazards near you here

What is it?#

Air quality is a measurement of how clean or polluted the air is. As a result of the Clean Air Act, the Environmental Protection Agency (EPA)measures five pollutants every day at over 1,000 locations including all large cities in the United States. The measurement is reported each day to the public as an Air Quality Index (AQI).

The five pollutants are ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Three of the five pollutants (carbon monoxide, sulfur dioxide, and nitrogen dioxide) mainly come from burning fossil fuels like gasoline, natural gas, oil, and coal. Ground-level ozone is formed when these three gasses are exposed to sunlight.

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Particulate matter (PM) refers to airborne solids and liquids that are small enough to be inhaled. Dust, pollen, and mold are usually larger than 10 microns or about 10 times smaller than the thickness of a human hair and are categorized as PM10. Fine particulate matter (PM2.5) are particles less than 30 times smaller than the thickness of a human hair or less than 2.5 microns. Fine particulate matter is small enough to be inhaled deep into the lungs. There are hundreds of sources of fine particulate matter (PM2.5) but the primary sources are burning fossil fuels in power plants, motor vehicles, and industries; smoke from forest fires, agricultural burning, and residential wood-burning; and volcanic eruptions and dust storms.

What do I need to know?#

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The AQI is like a thermometer that shows how polluted air is from 0-500 where 0 is the cleanest and 500 is the most polluted. When the AQI is below 50 it is considered safe for everyone.When it is above 50 then it begins to affect peoples' health. At first (between 50-100) it is a moderate concern for people with unusual sensitivity to pollution, between 100-150 it is unhealthy for sensitive groups like children with asthma, the elderely, and people with heart or respiratory disease. Above 150 it becomes unhealthy for everyone and above 300 it is an emergency that can have serious health effects on everyone.

How does it affect my health and property values?#

Breathing polluted air has serious health effects and increases the number of asthma attacks, strokes, heart attacks, and respiratory infections; irritates the lungs; and reduces lung function and the bodies ability to transport oxygen. Prolonged exposure to air pollution is also known to cause permanent lung damage and reduce lifespan. When pregnant women are exposed to high levels of air pollution it increases the rate of preterm births and children exposed to air pollution experience decreased lung development and capacity. In addition, air pollution can impact lifestyle because of the reduced activity recommended at AQI levels above 150.

Air pollution also has a negative effect on property values. Housing prices in the United States are lower in areas with air pollution. Researchers have consistently found that property values are higher in areas with lower air pollution levels and have even increased in counties in the United States when air quality improved.

What can I do about it?#

You can avoid air pollution and limit the effects of air pollution on your health. Keep track of the AQI where you live and reduce your exposure and exertion levels when air pollution levels are high. The AQI is available online from the EPA and reported as part of daily weather reports and forecasts by some national media sources including CNN, The Weather Channel, and USA Today. For example, when the AQI is above 150, then everyone should limit prolonged or heavy exertion and the elderly and children should avoid it completely.

You can also reduce the amount of air pollution you produce by avoiding or reducing your use of fossil fuels by using public transportation, walking or using a bicycle; using more sustainable forms of energy including solar or wind; and by not burning wood or yard waste. Identify the possible sources of air pollution in your community and contact your local, state, and federal elected officials about your concerns and encourage policies, legislation, and infrastructure to reduce or eliminate air pollution. Suspected environmental violations (including air pollution) can also be reported directly to the EPA through their violations reporting website.

AreaHub’s Knowledge Center is updated regularly and provides information drawing upon scientific studies and sources.

Sources#