Research also indicates that ground-level ozone exposure may increase the risk of premature death from heart or lung disease. Some people are more sensitive to ozone than others. Sensitive groups include children, older adults; and, people with lung disease such as: asthma, emphysema, and chronic bronchitis. Even healthy adults who are active outdoors can experience ozone's harmful effects.
Just as ground-level ozone can make it harder for people to breathe, it also makes it harder for plants to breathe. EPA's Ozone National Ambient Air Quality Standards are intended to protect both human health and public welfare, which includes protecting vegetation.
EPA has indicated that reducing ground-level ozone can have the following impacts on vegetation:. For more information on ground-level ozone and agriculture, click here. Since , Central Texas has had ground-level ozone levels that are considered by EPA to be "unhealthy for sensitive groups" as early as March and as late as October.
The months when high ozone is most common are between May and June and between August and October. High ozone levels are less likely to occur on Sundays than any other day of the week due to lower mobile source emissions. The key difference between a high ozone day and a low ozone day is the weather.
If you have forgotten your password, we can send you a new one. Ozone occurs naturally at low concentrations throughout the Earth's atmosphere. In the stratosphere, which extends from about 10 to 50 km above the Earth's surface, ozone is 'good' as it protects life on Earth from the sun's ultraviolet rays.
This is why the world is trying to stop the manufacture and use of substances that damage the stratospheric ozone layer. In the troposphere, near the Earth's surface, human activities lead to ozone concentrations several times higher than the natural background level.
Too much of this ground-level ozone is 'bad' as it is harmful to breathe and also damages vegetation. Software updated on 09 November from version Code for developers. Systems Status. Legal notice. Creative commons license. CMS login. Toggle navigation Skip to content. Advanced search A-Z Glossary. Error Cookies are not enabled.
You must enable cookies before you can log in. Once released into the air these ozone-depleting substances degrade very slowly. They can remain for years as they move through the troposphere until they reach the stratosphere.
There they are broken down by the intensity of the sun's UV rays and release chlorine and bromine molecules, which destroy the "good" ozone. Scientists estimate that one chlorine atom can destroy , "good" ozone molecules. Even though we have reduced or eliminated the use of many ozone-depleting substances, their use in the past can still affect the protective ozone layer. Research indicates that depletion of the "good" ozone layer is being reduced worldwide. Thinning of the protective ozone layer can be observed using satellite measurements, particularly over the Polar Regions.
Ozone depletion can cause increased amounts of UV radiation to reach the Earth which can lead to more cases of skin cancer, cataracts, and impaired immune systems. Too much exposure to UV is believed to be contributing to the increase in melanoma, the most fatal of all skin cancers. Since , the risk of developing melanoma has more than doubled. UV can also damage sensitive crops, such as soybeans, and reduce crop yields. Some scientists suggest that marine phytoplankton, which are the base of the ocean food chain, are already under stress from UV radiation.
This stress could have adverse consequences for human food supplies from the oceans. The United States, along with over other countries, recognized the threats posed by ozone depletion and in 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. Warning labels must be placed on all products containing CFCs or similar substances and nonessential uses of ozone-depleting products are prohibited. Releases into the air of refrigerants used in car and home air conditioning units and appliances are also prohibited.
Some substitutes to ozone-depleting products have been produced and others are being developed. If the United States and other countries stop producing ozone-depleting substances, estimates suggest that natural ozone production should return the ozone layer to normal levels by about Ground-level or "bad" ozone is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen NOx and volatile organic compounds VOC in the presence of sunlight.
Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors and chemical solvents are some of the major sources of NOx and VOC. At ground level, ozone is a harmful pollutant. Ozone pollution is a concern during the summer months because strong sunlight and hot weather result in harmful ozone concentrations in the air we breathe. Many urban and suburban areas throughout the United States have high levels of "bad" ozone.
But many rural areas of the country are also subject to high ozone levels as winds carry emissions hundreds of miles away from their original sources. Breathing ozone can trigger a variety of health problems including chest pain, coughing, throat irritation and congestion.
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