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Outdoor Air

Air and Health

Since the 1950s, air quality has been a major public health and environmental concern. Local, state, and national programs have helped us learn more about the problems and how to solve them.

National air quality has improved since the early 1990's, but many challenges remain in protecting public health and the environment from air quality problems.

CDC works closely with the U.S. Environmental Protection Agency to provide air quality data on the tracking network and to better understand how air pollution affects our health. The Tracking Network includes information about the possible health effects of exposure to ozone, particulate matter (PM2.5), benzene, and formaldehyde.

Ground-Level Ozone

Ozone is a gas that you cannot see or smell. Ozone occurs naturally in the sky about 10 to 30 miles above the earth's surface. Sometimes, this ozone is called "good ozone" because it forms a layer that protects life on earth from the sun's harmful rays.

Ground-level ozone, on the other hand, can be bad for your health and the environment. Ground-level ozone forms when pollutants from cars and trucks, power plants, factories, and other sources come in contact with each other in heat and sunlight. Factors such as weather conditions and intensity of sunlight also play a part in how ozone is formed. Ground-level ozone is one of the biggest parts of smog, and it is usually worse in the summer months.

Your exposure to ozone depends mainly on where you live and work and how much time you spend outside. Everyone can have health problems from ozone. Symptoms might be very mild or more serious. People with lung disease, children, older adults, and people who are active outdoors are at the highest risk of having problems when ozone levels are unhealthy.

Many scientific studies have linked ground-level ozone contact to varied problems, such as

  • lung and throat irritation,
  • wheezing and breathing difficulties during exercise or outdoor activities,
  • coughing and pain when taking a deep breath,
  • aggravation of asthma, bronchitis, and emphysema, and
  • higher chance of getting respiratory illness like pneumonia or bronchitis.

As a result of these studies, scientists know that breathing in too much ozone can increase events such as

  • use of asthma medication,
  • absences from school,
  • visits to the emergency room and hospital admissions, and
  • premature death from heart and lung disease.

EPA's Air Quality Index, or AQI, is a tool to help you quickly learn when air pollution is likely to reach unhealthy levels. You can use the AQI to plan your daily activities to reduce exposure to ozone. When ozone levels are high, you can

  • reduce the amount of time you spend outside;
  • plan outdoor activities when ozone levels are lower, usually in the morning and evening;
  • do easier outdoor activities, such as walking instead of running; and
  • plan indoor activities.
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Particulate Matter

Particle pollution, or particulate matter, consists of particles that are in the air, including dust, dirt, soot and smoke, and little drops of liquid. Some particles, such as soot or smoke, are large or dark enough to be seen. Other particles are so small that you cannot see them.

Fine particulate matter size comparison

Particle pollution includes

  • coarse particles that are between 2.5 and 10 micrometers,
  • fine particles that are between 0.1 micrometers and 2.5 micrometers; also known as PM2.5, and
  • ultrafine particles that are smaller than 0.1 micrometers.

Particles bigger than 10 micrometers can irritate your eyes, nose, and throat but do not usually reach your lungs. Ten micrometers is about seven times thinner than one human hair.

Fine and ultrafine particles are the most concerning because they are most likely to cause health problems. Their small size allows them to get into the deep part of your lungs and even into your blood.

Being exposed to any kind of particulate matter has been linked to

  • increased emergency department visits and hospital stays for breathing and heart problems,
  • breathing problems,
  • asthma symptoms to get worse,
  • adverse birth outcomes, such as low birth weight,
  • decreased lung growth in children,
  • lung cancer, and
  • early deaths.

People who are at the highest risk of being bothered by particulate matter include

  • people with heart or lung diseases because they will feel the effects of particulate matter sooner and at lower ozone levels than less-sensitive people.
  • older adults because they may not know they have lung or heart disease. When particle levels are high, older adults are more likely than young adults to have to go to the hospital or die because the exposure to particle pollution has made their heart or lung disease worse.
  • children because they are still growing and spend more time at high activity levels. When children come in contact with particle pollution over a long period of time they may have problems as their lungs and airways are developing. This exposure may put them at risk for lowered lung function and other respiratory problems later in life. Children are more likely than adults to have asthma and other respiratory problems that can worsen when particle pollution is high.
  • infants because their lungs continue to develop after birth and can be impacted by air pollutants.
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Benzene is a chemical that is a colorless or light yellow liquid at room temperature. It has a sweet odor and is highly flammable. It evaporates into the air very quickly, but its vapor is heavier than air and may sink into low-lying areas.

Outdoor air contains low levels of benzene from tobacco smoke, gas stations, motor vehicle exhaust, and industrial emissions. The air around hazardous waste sites or gas stations can contain higher levels of benzene than in other areas. People working in industries that make or use benzene may be exposed to the highest levels of it. Tobacco smoke is also a major source of benzene exposure.

People who breathe in high levels of benzene may develop the following signs and symptoms within minutes to several hours:

  • Drowsiness
  • Dizziness
  • Rapid or irregular heartbeat
  • Headaches
  • Tremors
  • Confusion
  • Unconsciousness
  • Death (at very high levels)

The U.S. Department of Health and Human Services (DHHS) has determined that benzene causes cancer in humans. Long-term exposure to high levels of benzene in the air can cause leukemia, cancer of the blood-forming organs.

Read more about benzene’s health effects and how to reduce risks for exposure.

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At room temperature, formaldehyde is a colorless, flammable gas that has a distinct, pungent smell. It is produced by both human and natural sources.

The primary way you can be exposed to formaldehyde is by breathing air containing it. Everyone is exposed to small amounts of formaldehyde in air and some foods and products. Nasal and eye irritation, neurological effects, and increased risk of asthma and/or allergy have been observed in people who breathe in low levels of formaldehyde. Eczema and changes in lung function have been observed in people who breathe in formaldehyde at slightly higher levels.

The U.S. Department of Health and Human Services (DHHS) has determined that formaldehyde causes cancer in humans.

Read more about formaldehyde.

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