What Is the Air Quality Index and How Does the EPA Use It?

air quality index
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Air quality alerts on TV or radio are familiar occurrences in many cities. They let us know if outside air quality is safe or harmful to our health. This information is more significant for some people than others. You will want to take notice if you are active outdoors, or have children who play outside. Likewise, if you have heart or lung disease, or you are a senior, a failure to pay attention to air quality could pose substantial immediate health risks.

Why Air Quality Is Important

Air pollution presents a serious health risk. It is associated with stroke, heart disease, lung cancer, and both chronic and acute respiratory diseases, including asthma. Around the world, 91 percent of people lived in places that did not meet World Health Organization air quality guideline levels in 2016 and resulted in 4.2 million premature deaths.

Why EPA Uses the Air Quality Index

Local air quality can seriously affect your immediate and long-term health. And, like the weather, the EPA notes, it can fluctuate frequently. The Air Quality Index (AQI) is used by EPA to make air quality easy for the public to access and understand.

Air Quality Index

AQI is an index used to report the current air quality condition. It provides people with a snapshot of how clean or how polluted that air is, as well as associated health risks.

Checking the AQI is a frequent practice in some cities and during certain seasons or weather conditons. AQI helps us better plan our outdoor activities.

The U.S. Environmental Protection Agency (EPA) tracks five major air pollutants regulated by the Clean Air Act. These pollutants include ground-level ozone, particle or particulate matter pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. To help protect public health, the EPA has established national air quality standards for each of the five toxin categories. Among these pollutants, ground-level ozone and airborne particles represent the greatest risks to human health in the United States.

Signaling Air Quality

AQI values run from 0 to 500. The higher the number, the greater the level of air pollution, along with increased risk to human health. Within this range, the AQI is divided into six different categories, spanning from “Good” to “Hazardous.”

These categories include:

  • "Good" AQI is 0 to 50. Air quality is considered satisfactory, and air pollution poses little or no risk.
  • "Moderate" AQI is 51 to 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 who are unusually sensitive to ozone may experience respiratory symptoms.
  • "Unhealthy for Sensitive Groups" AQI is 101 to 150. Although the general public is not likely to be affected at this AQI range, people with lung disease, older adults, and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults, and children are at greater risk from the presence of particles in the air.
  • "Unhealthy" AQI is 151 to 200. Everyone may begin to experience some adverse health effects, and members of the sensitive groups may experience more serious effects.
  • "Very Unhealthy" AQI is 201 to 300. This would trigger a health alert signifying that everyone may experience more serious health effects.
  • "Hazardous" AQI greater than 300. This would trigger a health warnings of emergency conditions. The entire population is more likely to be affected.

AQI also operates on a six-color system that corresponds to the six danger categories. Colors range from green (good) and yellow (moderate) through orange (unhealthy for sensitive groups), red (unhealthy), purple (very unhealthy), and maroon (dangerous).

What AQI Levels Are Typical

According to the EPA, AQI values typically are below 100, with higher values registered at just a handful of times annually. Major cities usually suffer more air pollution than smaller ones, and as a result, may exceed 100 more frequently. Values over 200 are infrequent, and those over 300 are extremely rare. Such readings may occur during a forest fire, for example.

Air quality can also differ seasonally, as well as locally. For example, ozone values may be higher during warm months as sunlight and heat boost ozone formation. Carbon monoxide, on the other hand, may be higher during cold weather, which can restrict the efficiency of car emission control systems. Particle pollution can be more intense near high-traffic thoroughfares, especially during peak daily traffic.

It is unfortunate that the AQI is needed. It is an important tool, however, and health risks associated with poor air quality can be mitigated through its use.