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Outdoor Air

Air Contaminants


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.

Many urban areas tend to have higher levels of ground-level ozone. However, rural areas have ground-level ozone, too. Wind carries ozone and the pollutants that form it hundreds of miles from their original sources, and rural areas have sources of ozone that contribute to this problem.

Ozone and Health

When ozone levels are very high, everyone should be concerned about ozone exposure. But ozone bothers some people more than others, mainly when they are outside. People in these groups may feel the effects of ozone when they are outside for short periods of time, even if they are only doing light activities. Those most likely to be bothered by ozone include

  • people with asthma or lung disease because they will feel the effects of ozone sooner and at lower ozone levels than less-sensitive people.
  • children who spend a lot of time outdoors. Children are also more likely than adults to have asthma, which may be aggravated when they breathe in ozone. Being exposed to ozone for short periods of time over many years may cause children to have more breathing problems as adults.
  • older adults because they are more likely to have heart or lung disease.
  • active people of all ages who exercise or work hard outside because they are in contact with ozone more than people who spend more time indoors.
  • infants because their lungs continue to develop after birth and can be impacted by air pollutants.

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

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

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.

Protect yourself and your family

EPA's Air Quality Index, or AQI, is a tool to help you quickly learn when air pollution is likely to reach unhealthy levels. Local TV stations, radio programs, and newspapers carry these air quality forecasts to tell you when particle levels are likely to be unhealthy. You can use the AQI to plan your daily activities to reduce exposure to ozone.

Your exposure to ozone depends mainly on where you live and work and how much time you spend outside. 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.

Particle pollution can come from primary or secondary sources. A primary source, such as wood stoves or forest fires, lets off particle pollution directly. A secondary source lets off gases that react and form particles. Examples of secondary sources are coal fires and power plants. Particle pollution also comes from motor vehicles, factories, and construction sites. These can be primary or secondary sources. Particle pollution can be a problem at different times of the year, depending on where you live.

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.

Particulate Matter and Health

Being exposed to any kind of particulate matter may cause

  • increased emergency department visits and hospital stays for breathing and heart problems,
  • worsened asthma symptoms,
  • adverse birth outcomes,
  • breathing problems,
  • 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.

Protect yourself and your family

EPA's Air Quality Index, or AQI, is a tool to help you quickly learn when air pollution is likely to reach unhealthy levels. Local TV stations, radio programs, and newspapers carry these air quality forecasts to tell you when particle levels are likely to be unhealthy. You can use the AQI to plan your daily activities to reduce exposure to particle pollution.

When particle pollution levels are high, you can

  • reduce the amount of time you spend outside;
  • do easier outdoor activities, such as walking instead of running or using a riding lawn mower instead of a push mower; and
  • exercise away from roads and highways. Particle pollution is usually worse near these areas.

If you have one of the following diseases, you may experience some effects from particle pollution:

Lung disease

  • You may not be able to breathe as deeply or strongly as you usually do.
  • You may cough more, have chest pain, wheeze, feel like you can't catch your breath, or be tired more than usual.

Heart disease

  • Coming in contact with particle pollution can cause serious problems in a short period of time, such as a heart attack without any warning signs.
  • Symptoms, including chest pain or tightness, fast heartbeat, feeling out of breath, and feeling tired more than usual, may be signs of a serious problem. If you have any of these signs, follow your doctor's advice and contact your doctor if the symptoms last longer than usual or worsen.


  • Follow your asthma management plan when particle levels are high.
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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. It dissolves only slightly in water and will float on top of water.

Benzene is formed from both natural processes and human activities. Natural sources of benzene include volcanoes and forest fires. It is also a natural part of crude oil, gasoline, and cigarette smoke. This chemical is widely used in the United States, and ranks in the top 20 chemicals for production volume.

Some industries use benzene to make other chemicals that are used to make plastics, resins, and nylon and synthetic fibers. Benzene is also used to make some types of lubricants, rubbers, dyes, detergents, drugs, and pesticides.

Outdoor air contains low levels of benzene from tobacco smoke, gas stations, motor vehicle exhaust, and industrial emissions. Indoor air generally contains levels of benzene higher than those in outdoor air. The benzene in indoor air comes from products that contain benzene such as glues, paints, furniture wax, and detergents. 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.

Benzene and Health

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)

Eating foods or drinking beverages containing high levels of benzene can cause the following symptoms within minutes to several hours:

  • Vomiting
  • Irritation of the stomach
  • Dizziness
  • Sleepiness
  • Convulsions
  • Rapid or irregular heartbeat
  • Death (at very high levels)

If a person vomits because of swallowing foods or beverages containing benzene, the vomit could be sucked into the lungs and cause breathing problems and coughing. Direct exposure of the eyes, skin, or lungs to benzene can cause tissue injury and irritation. Showing these signs and symptoms does not necessarily mean that a person has been exposed benzene.

Long-term exposure

The major effect of benzene from long-term exposure is on the blood. (Long-term exposure means exposure of a year or more.) Benzene causes harmful effects on the bone marrow and can cause a decrease in red blood cells, leading to anemia. It can also cause excessive bleeding and can affect the immune system, increasing the chance for infection.

Some women who breathed high levels of benzene for many months had irregular menstrual periods and a decrease in the size of their ovaries. It is not known whether benzene exposure affects the developing fetus in pregnant women or fertility in men.

Animal studies have shown low birth weights, delayed bone formation, and bone marrow damage when pregnant animals breathed benzene.

The 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.

Protect yourself and your family

First, if the benzene was released into the air, get fresh air by leaving the area where the benzene was released. Moving to an area with fresh air is a good way to reduce the possibility of death from exposure to benzene in the air.

  • If the benzene release was outside, move away from the area where the benzene was released.
  • If the benzene release was indoors, get out of the building.

If you are near a release of benzene, emergency coordinators may tell you to either evacuate the area or to "shelter in place" inside a building to avoid being exposed to the chemical. For more information on evacuation during a chemical emergency, see "Facts About Evacuation." For more information on sheltering in place during a chemical emergency, see "Facts About Sheltering in Place."

If you think you may have been exposed to benzene, you should remove your clothing, rapidly wash your entire body with soap and water, and get medical care as quickly as possible. Read more about benzene protection and what to do if you get it on your skin or clothes.

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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. Small amounts of formaldehyde are naturally produced by plants, animals, and humans.

Formaldehyde is used in the production of fertilizer, paper, plywood, and urea-formaldehyde resins. It is also used as a preservative in some foods and in many products used around the house, such as antiseptics, medicines, and cosmetics.

The primary way you can be exposed to formaldehyde is by breathing air containing it. Releases of formaldehyde into the air occur from industries using or manufacturing formaldehyde, wood products (such as particle-board, plywood, and furniture), automobile exhaust, cigarette smoke, paints and varnishes, and carpets and permanent press fabrics. The highest potential exposure occurs in the formaldehyde-based resins industry.

Formaldehyde and Health

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

Protect yourself and your family.

Formaldehyde is usually found in the air, and levels are usually higher indoors than outdoors. Opening windows and using fans to bring fresh air indoors are the easiest ways to lower levels in the house. Not smoking and not using unvented heaters indoors can lower the formaldehyde levels.

Formaldehyde is given off from a number of products used in the home. Removing formaldehyde sources in the home can reduce exposure. Providing fresh air, sealing unfinished manufactured wood surfaces, and washing new permanent press clothing before wearing can help lower exposure. Read more information about formaldehyde here.

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