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) and your local air quality agency have been 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 simple information about your local air quality, how unhealthy air may affect you, and how you can protect your health.

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 what associated health effects might be a concern. 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 ozoneparticle pollutioncarbon monoxide, and sulfur dioxide. For each of these pollutants, EPA has established national air quality standards to protect public health. EPA is currently reviewing the national air quality standard for nitrogen dioxide. If the standard is revised, the AQI will be revised as well.

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, while an AQI value over 300 represents air quality so hazardous that everyone may experience serious effects.

An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values at or below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy—at first for certain sensitive groups of people, then for everyone as AQI values increase.

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. These raw 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. 2

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 are 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 about 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 alerting 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.

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 are infrequent, and AQI values above 300 are extremely rare—they generally occur only during events such as forest fires. You can compare the air quality of U.S. cities and find out about quality trends in your area by visiting “AirCompare” at www.epa.gov/aircompare/.

AQI values can 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 also can 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. And particle pollution can be high any time of day, and is often elevated near busy roadways, especially during morning or evening rush hours.

How can I avoid being exposed to unhealthy air?

You can take simple steps to reduce your exposure to unhealthy air. First, you need to find out whether AQI levels are a concern in your area. You can do this, as described previously, by visiting the AIRNow Web site, signing up for EnviroFlash, or checking your local media. If the AQI for ozone, particle pollution, carbon monoxide, or sulfur dioxide is a concern in your area, you can learn what steps to take to protect your health by checking the charts on the following pages. Two important terms you will need to understand are:

  • Prolonged exertion. This means any outdoor activity that you’ll be doing intermittently for several hours and 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 how much time you spend on this type of activity.
  • Heavy exertion. This means intense outdoor activities that cause you to breathe hard. When air quality is unhealthy, you can protect your health by reducing how much time you spend on this type of activity, or by substituting a less intense activity—for example, go for a walk instead of a jog. Be sure to reduce your activity level if you experience any unusual coughing, chest discomfort, wheezing, breathing difficulty, or unusual fatigue.

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

  • Good ozone is present naturally in the Earth’s upper atmosphere—approximately 6 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. This is when the weather conditions normally needed to form ground-level ozone—lots of sun—occur.

Who is most at risk?

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, including teenagers, 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.

How can I protect my health at different AQI values?

AQI Values Actions to Protect Your Health From Ozone
Good
(0 - 50)
None
Moderate
(51 - 100*)
Unusually sensitive people should consider reducing prolonged or heavy outdoor exertion.
Unhealthy for Sensitive Groups
(101 - 150)
The following groups should reduce prolonged or heavy outdoor exertion:
— People with lung disease, such as asthma
— Children and older adults
— People who are active outdoors
Unhealthy
(151 - 200)
The following groups should avoid prolonged or heavy outdoor exertion:
— People with lung disease, such as asthma
— Children and older adults
— People who are active outdoors
Everyone else should limit prolonged outdoor exertion.
Very Unhealthy
(201 - 300)
The following groups should avoid all outdoor exertion:
— People with lung disease, such as asthma
— Children and older adults
— People who are active outdoors
Everyone else should limit outdoor exertion.
* An AQI of 100 for ozone corresponds to an ozone level of 0.075 parts per million (averaged over 8 hours).

What are the health effects?

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

  • Irritate the respiratory system, causing coughing, throat soreness, 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, asthmatics 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 natural decline in lung function that occurs with age.
courtesy AirNow.gov
The EPA's Ozone Standard is exceeded at .071 ppm
Monitoring Station Current 1-hr Reading High 1-hr Reading Current 8-hr Average High 8-hr Average
South
West
East
Central
North
Today's highest 8-Hour Avg. at the Monitor
Have we exceeded the standard today?
Did we exceed the standard yesterday?


Data is 'real-time', preliminary and subject to change upon QA/QC by ODEQ and EPA
The Air quality Index (AQI) reflects the health concern and corresponds to the EPA's national pollutant standard. AQI's higher than 100 generally mean air quality unhealthy for sensitive groups and an exceedance of the pollutant's standard.
The AQI below reflects ozone.
 
Air Quality AQI
Good
0-49
Moderate
50-99
Unhealthy for
Sensitive Groups
100-149
Unhealthy
150-200
Indicates the highest pollutant index from midnight until the time the page was last updated, changing when a new high is reflected throughout the day.

PM2.5 refers to atmospheric particulate matter (PM) that have a diameter of less than 2.5 micrometers, which is about 3% the diameter of a human hair.

Commonly written as PM2.5, particles in this category are so small that they can only be detected with an electron microscope. They are even smaller than their counterparts PM10, which are particles that are 10 micrometers or less, and are also called fine particles.

Fine particles can come from various sources. They include power plants, motor vehicles, airplanes, residential wood burning, forest fires, agricultural burning, volcanic eruptions and dust storms. Some are emitted directly into the air, while others are formed when gases and particles interact with one another in the atmosphere.

Why is PM 2.5 dangerous?

Since they are so small and light, fine particles tend to stay longer in the air than heavier particles. This increases the chances of humans and animals inhaling them into their bodies. Owing to their minute size, particles smaller than 2.5 micrometers are able to bypass the nose and throat and penetrate deep into the lungs and some may even enter the circulatory system. Studies have found a close link between exposure to fine particles and premature death from heart and lung disease. Fine particles are also known to trigger or worsen chronic disease such as asthma, heart attack, bronchitis and other respiratory problems.

24-Hour PM2.5 Standard (µg/m3)

PM2.5
Air Quality Index
PM2.5 Health Effects
Precautionary Actions
0 to 12.0
Good
0 to 50
Little to no risk. None.
12.1 to 35.4
Moderate
51 to 100
Unusually sensitive individuals may experience respiratory symptoms. Unusually sensitive people should consider reducing prolonged or heavy exertion.
35.5 to 55.4
Unhealthy for Sensitive Groups
101 to 150
Increasing likelihood of respiratory symptoms in sensitive individuals, aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly. People with respiratory or heart disease, the elderly and children should limit prolonged exertion.
55.5 to 150.4
Unhealthy
151 to 200
Increased aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly; increased respiratory effects in general population. People with respiratory or heart disease, the elderly and children should avoid prolonged exertion; everyone else should limit prolonged exertion.
150.5 to 250.4
Very Unhealthy
201 to 300
Significant aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly; significant increase in respiratory effects in general population. People with respiratory or heart disease, the elderly and children should avoid any outdoor activity; everyone else should avoid prolonged exertion.
250.5 to 500.4
Hazardous
301 to 500
Serious aggravation of heart or lung disease and premature mortality in persons with cardiopulmonary disease and the elderly; serious risk of respiratory effects in general population. Everyone should avoid any outdoor exertion; people with respiratory or heart disease, the elderly and children should remain indoors.

Children, older adults and those who are suffering from lung and/or heart disease are especially vulnerable to the adverse effects of fine particles in the air and should take special precautions when ambient PM 2.5 crosses unhealthy levels.

How to read the PM 2.5 readings

Due to the many adverse effects fine particles can inflict on a large number of people, PM2.5 is one of the major pollutants closely monitored by health authorities around the world. You will most likely come across a dedicated column for PM2.5 alongside the Air Quality Index (AQI), Pollutants Standards Index (PSI) or the air quality standards adopted by your country. On a very clear and non-hazy day, the PM2.5 concentration can be as low as 5 µg/m3 or below. The 24-hour concentration of PM2.5 is considered unhealthy when it rises above 35.4 µg/m3.

Why 24-hour and not a shorter duration when evaluating the health impact of fine particles? This is because the potential damage caused by air pollutants depends not just on the concentration, but also on the duration of exposure. The longer you are exposed to PM2.5, the higher the risk of developing adverse effects caused by the exposure. That’s why a 24-hour measurement is a better reflection of the health effects of fine particles than say a three-hour reading.

The EPA's PM 2.5 Standard is exceeded at 36 µg/m3

Today's PM 2.5 Readings (µg/m3)

Monitoring Station Today's Average Today's AQI Past 24-hours Average Past 24-hours AQI
Central
South


Data is 'real-time', preliminary and subject to change upon QA/QC by ODEQ and EPA
The PM 2.5 Air Quality Index (AQI) reflects the health concern and corresponds to the EPA's national pollutant standard. PM 2.5 AQI's higher than 100 (35.4 µg/m3) generally mean air quality unhealthy for sensitive groups and an exceedance of the pollutant's standard.
The AQI below reflects PM 2.5.
 
Air Quality AQI
Good
0-50
Moderate
51-100
Unhealthy for
Sensitive Groups
101-150
Unhealthy
151-200
Very Unhealthy
201-300
Hazardous
301-500
Indicates the highest pollutant index from midnight until the time the page was last updated, changing when a new high is reflected throughout the day.

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