Ozone
When we are talking about ozone as a pollutant, we are talking about ground-level ozone. This pollutant is found in the troposphere (ground-level). The other common ozone is found in the stratosphere (upper atmosphere) and protects us from harmful ultraviolet rays from the sun. For more information about the difference between these pollutants review EPA's publication entitled Ozone: Good Up High, Bad Nearby.
Ozone is a gas composed of three atoms of oxygen. Ozone occurs both in the Earth's upper atmosphere and at ground level. Ozone can be good or bad, depending on where it is found:
Ground-level ozone is formed when volatile organic compounds (VOC's) and nitrogen oxides (NOx) react in the atmosphere with sunlight and heat. Since ozone requires sunlight and heat to form, it is only of concern from April through October.
Sources of VOC's and NOx:
- Automobiles
- Construction equipment
- Gas-powered lawn care equipment
- Power plants
- Industrial sources (I.E. manufacturing facilities)
- Residential use of solvents, cleaners, paints, etc.
- Industrial and residential furnaces
- Gasoline stations (fuel evaporation)
- Small businesses (coating operations, solvent use, boilers, printing operations, etc.)
Bad Ozone
In the Earth's lower atmosphere, near ground level, ozone is formed when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources react chemically in the presence of sunlight. Ozone at ground level is a harmful air pollutant.
Health Effects of Ozone
Ground-level ozone can cause the following health effects even at low concentrations:
- Aggravate asthma, or other respiratory illnesses
- Irritate respiratory systems causing coughing and throat irritation
- Inflame and damage cells that line the lungs
- Reduce lung capacity making it difficult to take deep breathes
- Increase susceptibility to respiratory illnesses
- Increase hospitalizations by aggravating respiratory illnesses
Good Ozone
Ozone occurs naturally in the Earth's upper atmosphere - 6 to 30 miles above the Earth's surface - where it forms a protective layer that shields us from the sun's harmful ultraviolet rays. Manmade chemicals are known to destroy this beneficial ozone. An area where the protective "ozone layer" has been significantly depleted-for example, over the North or South pole-is sometimes called "the ozone hole." The United States, along with over 180 other countries, recognized the threats posed by ozone depletion and in 1987 adopted a treaty called the Montreal Protocol to phase out the production and use of ozone-depleting substances. EPA has established regulations to phase out ozone-depleting chemicals in the United States. Learn more