Types of Ozone


What is it?

Though it acts as a protective layer high above the earth, ozone can be harmful to breathe. It is the prime ingredient of smog, in our cities.

Why is there a problem?

Ozone is not emitted directly into the air but rather is formed by gases called nitrogen oxides (NOx) and volatile organic compounds (VOCs) that react with oxygen in the air in the presence of strong sunlight, creating effects of concern when temperatures are higher during summer.

Ground-level ozone forms readily in the atmosphere in hot weather. On warm days, VOCs and NOx "bake" together in the sun forming ozone concentrations which can remain high over large regions. Many urban areas tend to have high ozone levels. However, areas downwind of urban settings are also subject to high ozone exposure, as winds carry VOCs and NOx from their original sources.

Changing weather patterns (especially the number of hot, sunny days) and periods of air stagnation create yearly differences in ozone concentrations. It is often difficult to make long-term predictions concerning ground-level ozone because the number of "bad" ozone days varies greatly from one year to the next and there are so many factors which influence ozone formation.

Health and environmental effects of ground-level ozone

When inhaled, ozone can damage the lungs.

Relatively low amounts of ozone can cause chest pain, coughing, nausea, throat irritation, and congestion. It may also worsen bronchitis, heart disease, emphysema, and asthma.

Healthy people as well as those with respiratory problems, experience breathing problems when exposed to ozone.

The Environmental Protection Agency has established a maximum ozone health standard. A single hour of exposure to ozone at this level is sufficient to cause negative respiratory effects. In fact, 13 million U.S. adults are currently exposed to ozone levels above the health standard for at least one hour in the summer. During heavy exercise these people are at particular risk for short-term health effects. Many more individuals may be repeatedly exposed to lower ozone levels which may cause long-term adverse effects. About 64 million people live in areas with ozone levels greater than the maximum health standard.

Ground-level ozone interferes with the production and storage of starches within plants, reducing their growth rates.

It damages the quality of crops (such as corn, wheat, and soybeans), making them less valuable on the market and can substantially reduce crop yield.

Ozone reduces the ability of trees and plants to fight disease. It is estimated that agricultural crop losses of $2 to $3 billion dollars per year can be attributable to ozone exposure. The extent of forest damage is currently being studied. Ozone has been shown to damage various tree seedlings.

What is being done about the problem?

The Clean Air Act of 1990 requires EPA, states, and cities to initiate a series of programs that will further reduce emissions of VOCs and NOX from cars, fuels, industrial and chemical facilities, power plants, and consumer and commercial products among other sources. Cleaner cars and fuels, new kinds of gasoline nozzles, enhanced vehicle inspection, and other programs will be phased in over the next decade.


What is it?

In the stratosphere, high altitude ozone forms a protective layer 10 to 35 miles above the earth to shield us from the sun's harmful ultraviolet (UV) rays. Ozone is naturally produced and destroyed at a constant rate in the stratosphere.

Why is there a problem?

Stratospheric ozone is gradually being destroyed by chemicals called chlorofluorocarbons (CFCs) and other ozone-depleting substances. These ozone depleters degrade slowly and can remain intact until they reach the stratosphere. There they are broken apart by the sun's ultraviolet rays. This reaction sets free the chlorine or bromine molecules of these chemicals, allowing them to attack and destroy the protective ozone blanket.

It can take decades for them to reach the upper atmosphere. Ozone-depleting substances released today will contribute to ozone destruction many years from now. One CFC molecule can lead to the elimination of 100,000 ozone molecules. Consequently, ozone is disappearing much faster than it is being replaced naturally.

Satellite information indicates ozone losses on as a global scale. The most significant losses have occurred over the North and South Poles, because ozone depletion occurs rapidly in extremely cold weather conditions. Fluctuating weather cycles affect the level of ozone in the stratosphere. This makes it difficult for scientists to accurately predict the future condition of the ozone layer.

Health and environmental effects if high-altitude ozone is decreased

If destruction of the ozone layer continues, more harmful ultraviolet rays will reach the earth's surface and its inhabitants, leading to increases in the number of skin cancer cases and eye cataracts (which can cause blindness). The United Nations estimates a 26 percent increase in skin cancer cases, 1.6 million more cataract cases, and 24,000 deaths from melanoma (a serious form of skin cancer) worldwide by the end of the decade.

Ozone depletion/increased ultraviolet rays will also damage UV-sensitive crops, such as soybeans.

Additionally, ozone depletion is suspected to cause decreases in phytoplankton, a plant within the ocean. Decreased phytoplankton could:

  1. reduce fish populations (since phytoplankton is an important plant/food source in the marine food chain).
  2. increase the level of carbon dioxide in the atmosphere, because plants "breathe in" carbon dioxide and "breathe out" oxygen.
Increased UV radiation can also be instrumental in forming more ground-level ozone.

What is being done about the problem?

In 1987 the United States entered into as a series of international agreements called the Montreal Protocol which were designed to limit and eventually eliminate world-wide production of ozone-depleting substances by the turn of the century. Under the Clean Air Act of 1990 the US Environmental Protection Agency (EPA) is accelerating the schedule for phasing out CFCs and certain other ozone-depleting substances to the end of 1995.

The Clean Air Act requires the use of written labels on all products containing CFCs or similar substances and prohibits non-essential ozone-depleting products such as fog horns. In addition, the CAA prohibits releasing car and home air conditioner refrigerants or appliance refrigerants into the atmosphere.


High Altitude Ozone:
  • Make sure that technicians working on your car air conditioner, home air conditioner, or refrigerator recover the refrigerant (This is required by law).
  • Have your car and home air conditioner units and refrigerator checked for leaks. When possible, repair leaky air conditioning units before refilling them.
  • Properly dispose of refrigeration or air conditioning equipment (This is required by law).
  • Protect yourself against intense sunburn. Wear UV-screening sunglasses and hats to shield yourself from harmful rays. Also, apply sunscreen.
Ground-Level Ozone:
  • Keep your automobile tuned-up and well-maintained.
  • Carpool and/or reduce driving.
  • Be careful not to spill gasoline when filling up your car or gasoline-powered lawn and garden equipment.
  • Make sure your tires are properly inflated and your wheels aligned.
  • Participate in your local utility's energy conservation programs.
  • Seal containers containing household cleaners, workshop chemicals and solvents, and garden chemicals to prevent volatile organic compounds (VOCs) from evaporating into the air.

[Text from U.S. EPA Publication, July 1997]r

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