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Bureau of Epidemiology

Environmental Epidemiology

Air Quality Index (AQI)

Frequently Asked Questions (FAQs)

Why is air quality important?

Local air quality affects how you live and breathe. Like the weather, it can change from day to day or even hour to hour. The U.S. Environmental Protection Agency (EPA), the Utah Department of Environmental Quality (UDEQ) and the Utah Department of Health (UDOH) are working to make information about outdoor air quality as easy to find and understand as weather forecasts. A key tool in this effort is the Air Quality Index, or AQI. EPA and local officials use the AQI to provide information about your local air quality, how unhealthy air may affect you, and how you can protect your health.

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What is the AQI?

The AQI is an index for reporting daily air quality. It tells you how clean or unhealthy your air is and how it might affect your health. The AQI focuses on health effects you may experience within a few hours or days after breathing unhealthy air. The AQI is calculated for four major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (both PM10 and 2.5), carbon monoxide, and sulfur dioxide. For each of these pollutants, the EPA has established national air quality standards to protect public health.

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How does the AQI work?

Think of the AQI as a yardstick that runs from 0 to 500. 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 represents good air quality with little or no potential to affect public health. An AQI value over 300 represents air quality so hazardous that even healthy people may experience serious problems. A value of 100 generally corresponds to the national air quality standard for all of the pollutants found on the AQI, which is the level the EPA has set to protect public health. AQI values at or below 100 are generally thought to be satisfactory or healthy. When AQI values are above 100, air quality is considered to be unhealthy - first for certain sensitive groups, then, as AQI values increase, for everyone.

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How is a community's AQI calculated and reported?

Each day, monitors record concentrations of the major pollutants at more than a thousand locations across the country. The monitoring data used by the AQI for Utah come from monitors managed by the Division of Air Quality. The real-time pollution numbers can be found at www.airquality.utah.gov.

These measurements are converted into a separate AQI value for each pollutant (ground-level ozone, particle pollution, carbon monoxide, and sulfur dioxide) using standard formulas developed by EPA. The highest of these AQI values is reported as the AQI value for that day. In large cities (more than 350,000 people), state and local agencies are required to report the AQI to the public daily. Many smaller communities also report the AQI as a public health service. When the AQI is above 100, agencies must also report which groups, such as children or people with asthma or heart disease, may be sensitive to that pollutant. If two or more pollutants have AQI values above 100 on a given day, agencies must report all the groups that might be sensitive to those pollutants. For example, if a community’s AQI is 130 for ozone and 101 for particle pollution, the AQI value for that day would be announced as 130 for ozone. The announcements would note that particle pollution levels were also high and would alert groups sensitive to ozone or particle pollution, educating them on how to protect their health.

Many cities also provide forecasts for the next day’s AQI. These forecasts help local residents protect their health by advising them to plan their strenuous outdoor activities for a time when air quality is better. The AQI is a national index, so the values and colors used to show local air quality and the levels of health concern are the same everywhere in the United States.

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Where can I find the AQI?

Checking local air quality is as easy as checking the weather. You can find the latest AQI values on the Internet and in your local media. You also can sign up to receive AQI forecasts by e-mail:

  • AQI on the Internet: The EPA and its federal, tribal, state, and local partners have developed the AIRNow website to give the public easy access to national air quality information. At www.airnow.gov, you will find daily AQI forecasts and real-time AQI conditions for more than 300 cities across the United States, with links to more detailed state and local air quality websites. AIRNow reports are displayed as maps you can use to quickly determine if the air quality is unhealthy near you.
  • AQI via e-mail: Sign up for EnviroFlash (www.enviroflash.info), a free service that will alert you via e-mail when air quality is forecast to be a concern in your area.
  • AQI via Division of Air Quality Liserv: Sign up for emails sent from the division during the winter PM2.5 and summer ozone seasons at http://www.deq.utah.gov/ListServ/.
  • AQI in the media: Many local media—television, radio, and newspapers, and some national media (such as USA Today, The Weather Channel, and CNN) provide daily air quality reports, often as part of the weather forecast.

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What are typical AQI values in most communities?

In many U.S. communities, AQI values are usually below 100, with higher values occurring just a few times a year. Larger cities typically have more air pollution than smaller cities, so their AQI values may exceed 100 more often. AQI values higher than 200 don’t occur very often, and AQI values above 300 are extremely rare—generally occurring only during events such as forest fires. You can compare the air quality of U.S. cities and find out about air quality trends in your area by visiting “Air Compare” at www.epa.gov/aircompare/. AQI values can also vary from one season to another.

In winter, carbon monoxide may be high in some areas because cold weather makes it difficult for car emission control systems to operate effectively. Ozone is often higher in warmer months, because heat and sunlight increase ozone formation. Particle pollution can be elevated any time of the year. AQI values can also vary depending on the time of day. Ozone levels often peak in the afternoon to early evening. Carbon monoxide may be a problem during morning or evening rush hours. Particle pollution can be high any time of day and is often elevated near busy roadways, especially during morning or evening rush hours.

There are two seasons with greater occurrences of poor air quality in Utah. Wintertime inversions contribute to higher PM2.5 levels and during the summer high temperatures and increased sunlight create more ozone.

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How can I avoid being exposed to unhealthy air?

There are some simple steps you can take to reduce your exposure to unhealthy air. First, check whether AQI levels are a concern in your area. You can do this by visiting www.AirNow.gov or checking real-time air monitoring available at www.airquality.utah.gov. If the AQI for ozone or particle pollution is a concern in your area, you can learn what steps to take to protect your health by checking the charts in "How do I use the AQI charts?". Two important terms you will need to understand:

  • Prolonged exertion: This includes any outdoor activity that you’ll be doing intermittently for several hours that makes you breathe slightly harder than normal. A good example of this is working in the yard for part of a day. When air quality is unhealthy, you can protect your health by reducing the amount of time you spend on this type of activity or vary the time of day you are outdoors to avoid periods of higher pollution.
  • Heavy exertion: This includes intense outdoor activities that cause you to breathe hard. When air quality is unhealthy, you can protect your health by reducing the amount of time you spend on this type of activity, or by substituting a less intense activity—for example, walk instead of jog. Be sure to reduce your activity level if you experience any unusual coughing, chest discomfort, wheezing, breathing difficulty, or more fatigue than normal.

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How do I use the AQI charts?

Chart 1 tells you the level of health concern that corresponds to each AQI value as well as the values of ozone and PM2.5 that correspond to each AQI level. It also explains what each level means to your health. Once you know the current AQI for the day continue to chart 2.

Chart 2 describes the symptoms outdoor air may cause you to experience that day and actions you can take to avoid those symptoms.

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What is ozone?

Ozone is a gas found in the air we breathe. Ozone can be good or bad, depending on where it occurs:

  • Good ozone is present naturally in the Earth’s upper atmosphere—approximately six to 30 miles above the Earth’s surface. This natural ozone shields us from the sun’s harmful ultraviolet rays.
  • Bad ozone forms near the ground when pollutants (emitted by sources such as cars, power plants, industrial boilers, refineries, and chemical plants) react chemically in sunlight. Ozone pollution is more likely to form during warmer months when higher temperatures and increased sunlight are available. Ozone is highest during the hottest periods of the day, usually from 10am to 6pm.

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Who is most at risk from ozone?

Several groups of people are particularly sensitive to ozone, especially when they are active outdoors. This is because ozone levels are higher outdoors, and physical activity causes faster and deeper breathing, drawing more ozone into the body.

  • People with lung diseases such as asthma, chronic bronchitis, and emphysema can be particularly sensitive to ozone. They will generally experience more serious health effects at lower levels. Ozone can aggravate their diseases, leading to increased medication use, doctor and emergency room visits, and hospital admissions.
  • Children are at higher risk from ozone exposure because they often play outdoors in warmer weather when ozone levels are higher, they are more likely to have asthma (which may be aggravated by ozone exposure), and their lungs are still developing.
  • Older adults may be more affected by ozone exposure, possibly because they are more likely to have pre-existing lung disease.
  • Active people of all ages who exercise or work vigorously outdoors are at increased risk.
  • Some healthy people are more sensitive to ozone. They may experience health effects at lower ozone levels than the average person even though they have none of the risk factors listed above. There may be a genetic basis for this increased sensitivity.

In general, as concentrations of ground-level ozone increase, more people begin to experience more serious health effects. When levels are very high, everyone should be concerned about ozone exposure.

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What are the health effects of ozone?

Ozone affects the lungs and respiratory system in many ways. It can:

  • Irritate the respiratory system, causing coughing, sore throat, airway irritation, chest tightness, or chest pain when taking a deep breath.
  • Reduce lung function, making it more difficult to breathe as deeply and vigorously as you normally would, especially when exercising. Breathing may start to feel uncomfortable, and you may notice that you are taking more rapid and shallow breaths than normal.
  • Inflame and damage the cells that line the lungs. Within a few days, the damaged cells are replaced and the old cells are shed—much like the way your skin peels after sunburn. Studies suggest that if this type of inflammation happens repeatedly, lung tissue may become permanently scarred and lung function may be permanently reduced.
  • Make the lungs more susceptible to infection. Ozone reduces the lung’s defenses by damaging the cells that move particles and bacteria out of the airways and by reducing the number and effectiveness of white blood cells in the lungs.
  • Aggravate asthma. When ozone levels are unhealthy, more people with asthma have symptoms that require a doctor’s attention or the use of medication. Ozone makes people more sensitive to allergens—the most common triggers for asthma attacks. Also, people with asthma may be more severely affected by reduced lung function and airway inflammation. People with asthma should ask their doctor for an asthma action plan and follow it carefully when ozone levels are unhealthy.
  • Aggravate other chronic lung diseases such as emphysema and bronchitis. As concentrations of ground-level ozone increase, more people with lung disease visit doctors or emergency rooms and are admitted to the hospital.
  • Cause permanent lung damage. Repeated short-term ozone damage to children’s developing lungs may lead to reduced lung function in adulthood. In adults, ozone exposure may accelerate the decline in lung function that naturally occurs with age.

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What is particle pollution?

Particle pollution (also known as “particulate matter”) consists of a mixture of solids and liquid droplets. Some particles are emitted directly; others form when pollutants emitted by various sources react in the atmosphere. Particle pollution levels can be very unhealthy and even hazardous during events such as forest fires.

Particles come in a range of sizes. Those less than 10 micrometers in diameter (smaller than the width of a single human hair) are so small that they can get into the lungs, where they can cause serious health problems.

  • Fine particles. The smallest particles (those 2.5 micrometers or less in diameter) are called “fine” particles. These particles are so small they can be detected only with an electron microscope. Major sources of fine particles include motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, some industrial processes, and other combustion processes.
  • Coarse particles. Particles between 2.5 and 10 micrometers in diameter are referred to as “coarse.” Sources of coarse particles include crushing or grinding operations and dust stirred up by vehicles traveling on roads.

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What are the health effects and who is most at risk from particle pollution?

Particles smaller than 10 micrometers in diameter can cause or aggravate a number of health problems and have been linked with illnesses and deaths from heart or lung disease. These effects have been associated with both short-term exposures (usually over 24 hours, but possibly as short as one hour) and long-term exposures (years).

Sensitive groups for particle pollution include people with heart or lung disease (including heart failure and coronary artery disease, or asthma and chronic obstructive pulmonary disease), older adults (who may have undiagnosed heart or lung disease), and children. The risk of heart attacks, and thus the risk from particle pollution, may begin as early as the mid-40s for men and mid-50s for women.

  • When exposed to particle pollution, people with heart or lung diseases and older adults are more likely to visit emergency rooms, be admitted to hospitals, or in some cases, even die.
  • Exposure to particle pollution may cause people with heart disease to experience chest pain, palpitations, shortness of breath, and fatigue. Particle pollution has also been associated with cardiac arrhythmias and heart attacks.
  • When exposed to high levels of particle pollution, people with existing lung disease may not be able to breathe as deeply or vigorously as they normally would. They may experience symptoms such as coughing and shortness of breath. Healthy people also may experience these effects, although they are unlikely to experience more serious effects.
  • Particle pollution also can increase susceptibility to respiratory infections and can aggravate existing respiratory diseases, such as asthma and chronic bronchitis, causing more use of medication and more doctor visits.

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Sources

U.S. Environmental Protection Agency (EPA). 2009. AQI Air Quality Index, A Guide to Air Quality and Your Health. Retrieved from http://www.epa.gov/airnow/aqi_brochure_08-09.pdf

U.S. Environmental Protection Agency (EPA). 2012. Patient Exposure and the Air Quality Index. Retrieved from http://www.epa.gov/o3healthtraining/aqi.html

U.S. Environmental Protection Agency (EPA). 2006. Guidelines for the Reporting of Daily Air Quality-the Air Quality Index (AQI). Retrieved from http://www.epa.gov/ttn/oarpg/t1/memoranda/rg701.pdf

AIRNow.gov. (2010). AQI Calculator: Concentration to AQI. Retrieved from http://airnow.gov/index.cfm?action=resources.conc_aqi_calc

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