Ozone - O3, is a molecule that consists of three oxygen atoms bonded together. The ozone layer in the stratosphere absorbs UV radiation and creates a warm layer of air in the stratosphere and is therefore responsible for the thermal structure of the stratosphere. Ozone that is present in the troposphere is mostly a result of anthropogenic pollution and therefore higher concentrations are found in urban areas. Ozone is involved with NOx in the photochemical production of many of the constituents of pollution environments (see nitrogen oxides and hydroxyl radicals.)
[Chemical and Engineering News; v72; 6-7; 1994.]
[Aviation Week and Space Technology; v140; 20-21; 1994.]
Atmospheric Chemistry Glossary
Ozone is a special form of oxygen and one of the most powerful oxidizing agents known. It destroys vegetation and seriously affects the respiratory tract.
Ozone: a gas composed of three atoms of oxygen
Ozone is a bluish gas that is harmful to breathe. Nearly 90% of the Earth's ozone is in the stratosphere and is referred to as the ozone layer. Ozone absorbs a band of ultraviolet radiation called UVB that is particularly harmful to living organisms. The ozone layer prevents most UVB from reaching the ground.
http://www.epa.gov/ozone
GOOD UP HIGH
What is Ozone?
Ozone is a gas that forms in the atmosphere when 3 atoms of oxygen are combined (O3). It is not emitted directly into the air, but at ground level is created by a chemical reaction between oxides of nitrogen (NOx), and volatile organic compounds (VOC) in the presence of sunlight. Ozone has the same chemical structure whether it occurs high above the earth or at ground level and can be "good" or "bad," depending on its location in the atmosphere.
How Can Ozone Be Both Good and Bad?
Ozone occurs in two layers of the atmosphere. The layer surrounding the earth's surface is the troposphere. Here, ground-level or "bad" ozone is an air pollutant that damages human health, vegetation, and many common materials. It is a key ingredient of urban smog. The troposphere extends to a level about 10 miles up, where it meets the second layer, the stratosphere. The stratospheric or "good" ozone layer extends upward from about 10 to 30 miles and protects life on earth from the sun's harmful ultraviolet rays (UV-b).
What is Happening to the "Good" Ozone Layer?
Ozone occurs naturally in the stratosphere and is produced and destroyed at a constant rate. But this "good" ozone is gradually being destroyed by manmade chemicals called chlorofluorocarbons (CFCs), halons, and other ozone depleting substances (used in coolants, foaming agents, fire extinguishers, and solvents). These ozone depleting substances degrade slowly and can remain intact for many years as they move through the troposphere until they reach the stratosphere. There they are broken down by the intensity of the sun's ultraviolet rays and release chlorine and bromine molecules, which destroy "good" ozone. One chlorine or bromine molecule can destroy 100,000 ozone molecules, causing ozone to disappear much faster than nature can replace it.
It can take years for ozone depleting chemicals to reach the stratosphere, and even though we have reduced or eliminated the use of many CFCs, their impact from years past is just starting to affect the ozone layer. Substances released into the air today will contribute to ozone destruction well into the future.
Satellite observations indicate a world-wide thinning of the protective ozone layer. The most noticeable losses occur over the North and South Poles because ozone depletion accelerates in extremely cold weather conditions.
How Does the Depletion of "Good" Ozone Affect Human Health and the Environment?
As the stratospheric ozone layer is depleted, higher UV-b levels reach the earth's surface. Increased UV-b can lead to more cases of skin cancer, cataracts, and impaired immune systems. Damage to UV-b sensitive crops, such as soybeans, reduces yield. High altitude ozone depletion is suspected to cause decreases in phytoplankton, a plant that grows in the ocean. Phytoplankton is an important link in the marine food chain and, therefore, food populations could decline. Because plants "breathe in" carbon dioxide and "breathe out" oxygen, carbon dioxide levels in the air could also increase. Increased UV-b radiation can be instrumental in forming more ground-level or "bad" ozone.
What is Being Done About the Depletion of Good Ozone?
The Montreal Protocol, a series of international agreements on the reduction and eventual elimination of production and use of ozone depleting substances, became effective in 1989. Currently, 160 countries participate in the Protocol. Efforts will result in recovery of the ozone layer in about 50 years. In the United States, the U.S. Environmental Protection Agency (EPA) continues to establish regulations to phase out these chemicals. The Clean Air Act requires warning labels on all products containing CFCs or similar substances, prohibits nonessential ozone depleting products, and prohibits the release of refrigerants used in car and home air conditioning units and appliances into the air.
BAD NEARBY
What Causes "Bad" Ozone?
Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC, also known as ozone precursors. Strong sunlight and hot weather cause ground-level ozone to form in harmful concentrations in the air. Many urban areas tend to have high levels of "bad" ozone, but other areas are also subject to high ozone levels as winds carry NOx emissions hundreds of miles away from their original sources.
Ozone concentrations can vary from year to year. Changing weather patterns (especially the number of hot, sunny days), periods of air stagnation, and other factors that contribute to ozone formation make long-term predictions difficult.
How Does "Bad" Ozone Affect Human Health and the Environment?
Repeated exposure to ozone pollution may cause permanent damage to the lungs. Even when ozone is present in low levels, inhaling it triggers a variety of health problems including chest pains, coughing, nausea, throat irritation, and congestion. It also can worsen bronchitis, heart disease, emphysema, and asthma, and reduce lung capacity.
Healthy people also experience difficulty in breathing when exposed to ozone pollution. Because ozone pollution usually forms in hot weather, anyone who spends time outdoors in the summer may be affected, particularly children, the elderly, outdoor workers and people exercising. Millions of Americans live in areas where the national ozone health standards are exceeded.
Ground-level ozone damages plant life and is responsible for 500 million dollars in reduced crop production in the United States each year. It interferes with the ability of plants to produce and store food, making them more susceptible to disease, insects, other pollutants, and harsh weather. "Bad" ozone damages the foliage of trees and other plants, ruining the landscape of cities, national parks and forests, and recreation areas.
What is Being Done About Bad Ozone?
The Clean Air Act Amendments of 1990 require EPA, states, and cities to implement programs to further reduce emissions of ozone precursors from sources such as cars, fuels, industrial facilities, power plants, and consumer/commercial products. Power plants will be reducing emissions, cleaner cars and fuels are being developed, many gas stations are using special nozzles at the pumps to recapture gasoline vapors, and vehicle inspection programs are being improved to reduce emissions.
The ultimate responsibility for our environment is our own. Minor lifestyle changes can result in major air quality improvements.
Six Principal Pollutants - Ozone (O3)
Nature and Sources of the Pollutant: Ground-level ozone (the primary constituent of smog) is the most complex, difficult to control, and pervasive of the six principal air pollutants. Unlike other pollutants, ozone is not emitted directly into the air by specific sources. Ozone is created by sunlight acting on NOx and VOC in the air. There are thousands of types of sources of these gases. Some of the common sources include gasoline vapors, chemical solvents, combustion products of fuels, and consumer products. Emissions of NOx and VOC from motor vehicles and stationary sources can be carried hundreds of miles from their origins, and result in high ozone concentrations over very large regions.
Health and Environmental Effects: Scientific evidence indicates that ground-level ozone not only affects people with impaired respiratory systems (such as asthmatics), but healthy adults and children as well. Exposure to ozone for 6 to 7 hours, even at relatively low concentrations, significantly reduces lung function and induces respiratory inflammation in normal, healthy people during periods of moderate exercise. It can be accompanied by symptoms such as chest pain, coughing, nausea, and pulmonary congestion. Recent studies provide evidence of an association between elevated ozone levels and increases in hospital admissions for respiratory problems in several U.S. cities. Results from animal studies indicate that repeated exposure to high levels of ozone for several months or more can produce permanent structural damage in the lungs. EPA's health-based national air quality standard for ozone is currently set at 0.12 ppm (measured as the second daily 1-hour maximum concentration). Ozone is responsible for approximately 1 to 2 billion dollars of agricultural crop yield loss in the U.S. each year. Ozone also damages forest ecosystems in California and the eastern U.S. New scientific studies indicate that ozone causes adverse health and environmental effects at lower concentrations and longer periods of exposure than the current standards. As a result, EPA is reviewing whether revisions to the current ozone standard are warranted.
Trends in Ozone Levels: Trends in ozone concentrations are influenced by year-to-year changes in meteorological conditions as well as changes in emissions. National ozone concentrations in 1995 were 6 percent lower than those in 1986. However, between 1994 and 1995, national ozone concentrations increased 4 percent. Because of the hot, dry summer, meteorological conditions in 1995 were conducive to ozone formation, especially from the Midwest and Gulf States to the eastern U.S. Emissions of VOC (which contribute to ozone formation) decreased 9 percent between 1986 and 1995 and 2 percent between 1994 and 1995. Based on air quality monitoring data, over 70 million people lived in counties with air quality levels above EPA's health-based national air quality standard for ozone in 1995. In 1994, EPA established a new monitoring network to gather further data on causes of ozone air pollution. This network of monitors, called Photochemical Assessment Monitoring Stations (PAMS), is located in ozone nonattainment areas of the U.S. which are classified as "serious" "severe," or "extreme." Concentration data were collected in 22 areas for ozone, NOx , and a variety of VOC (including several toxic air pollutants) that form ozone. The majority of the PAMS sites showed decreases in the monitored concentrations of toxic air pollutants and ozone-forming VOC.
Ozone (O3) is a photochemical oxidant and the major component of smog. While O3 in the upper atmosphere is beneficial to life by shielding the earth from harmful ultraviolet radiation from the sun, high concentrations of O3 at ground level are a major health and environmental concern. O3 is not emitted directly into the air but is formed through complex chemical reactions between precursor emissions of volatile organic compounds (VOC) and oxides of nitrogen (NOx) in the presence of sunlight. These reactions are stimulated by sunlight and temperature so that peak O3 levels occur typically during the warmer times of the year. Both VOCs and NOx are emitted by transportation and industrial sources. VOCs are emitted from sources as diverse as autos, chemical manufacturing, dry cleaners, paint shops and other sources using solvents.
The reactivity of O3 causes health problems because it damages lung tissue, reduces lung function and sensitizes the lungs to other irritants. Scientific evidence indicates that ambient levels of O3 not only affect people with impaired respiratory systems, such as asthmatics, but healthy adults and children as well. Exposure to O3 for several hours at relatively low concentrations has been found to significantly reduce lung function and induce respiratory inflammation in normal, healthy people during exercise. This decrease in lung function generally is accompanied by symptoms including chest pain, coughing, sneezing and pulmonary congestion.
1-Hour Ozone Standard
The ozone threshold value is 0.12 parts per million (ppm), measured as 1-hour average concentration. An area meets the ozone NAAQS if there is no more than one day per year when the highest hourly value exceeds the threshold. (If monitoring did not take place every day because of equipment malfunction or other operational problems, actual measurements are prorated for the missing days. The estimated total number of above-threshold days must be 1.0 or less.) To be in attainment, an area must meet the ozone NAAQS for three consecutive years.
Air quality ozone value is estimated using EPA guidance for calculating design values (Laxton Memorandum, June 18, 1990). Generally, the fourth highest monitored value with 3 complete years of data is selected as the updated air quality value because the standard allows one exceedance for each year. It is important to note that the 1990 Clean Air Act Amendments required that ozone nonattainment areas be classified on the basis of the design value at the time the Amendments were passed, generally the 1987-89 period was used.
The strong seasonality of O3 levels makes it possible for areas to limit their O3 monitoring to a certain portion of the year, termed the O3 season. Peak O3 concentrations typically occur during hot, dry, stagnant summertime conditions, i.e., high temperature and strong solar insolation. The length of the O3 season varies from one area of the country to another. May through October is typical, but states in the south and southwest may monitor the entire year. Northern states have shorter O3 seasons, e.g., May through September for North Dakota. This analysis uses these O3 seasons to ensure that the data completeness requirements apply to the relevant portions of the year.
On November 6, 1991, most areas of the country were designated nonattainment or unclassifiable/attainment. These terms are defined as follows:
Nonattainment
any area that does not meet (or that contributes to ambient air quality in a nearby area that does not meet) the national primary or secondary ambient air quality standard for the pollutant.
Attainment
any area that meets the national primary or secondary ambient air quality standard for the pollutant.
Unclassifiable
any area that cannot be classified on the basis of available information as meeting or not meeting the national primary or secondary ambient air quality standard for the pollutant.
Those areas designated nonattainment were also classified as follows:
Extreme
Area has a design value of 0.280 ppm and above.
Severe 17
Area has a design value of 0.190 up to 0.280 ppm and has 17 years to attain.
Severe 15
Area has a design value of 0.180 up to 0.190 ppm and has 15 years to attain.
Serious
Area has a design value of 0.160 up to 0.180 ppm.
Moderate
Area has a design value of 0.138 up to 0.160 ppm.
Marginal
Area has a design value of 0.121 up to 0.138 ppm.
Submarginal
Kansas City was the only area classified submarginal, but it has been redesignated attainment. This category includes areas that violate the ozone standard and have a design value of less than 0.121 parts per million. This occurs when there is not a complete set of data so that the estimated design value is higher than the ozone standard exceedance rate of 1.0 per year even though the estimated design value is less than the level of the standard.
Sec. 185A (Previously called Transitional)
an area designated as an ozone nonattainment area as of the date of enactment of the Clean Air Act Amendments of 1990 and has not violated the national primary ambient air quality standard for ozone for the 36-month period commencing on January 1, 1987 and ending on December 31, 1989. Twelve areas were classified transitional in 1991. Section 185A. "Transitional Areas" lists the requirements for these areas.
Incomplete (or No) Data
an area designated as an ozone nonattainment area as of the date of enactment of the Clean Air Act Amendments of 1990 and did not have sufficient data to determine if it is or is not meeting the ozone standard.
Sections 107(d)(4)(A) and 181 of the Clean Air Act lists the requirements for designations and classifications of ozone areas.
New 8-Hour Ozone Standard
EPA issued final air quality standards for particulate matter and ozone (otherwise known as soot and smog) on July 16, 1997. On May 14, 1999, the U.S. Court of Appeals for the District of Columbia Circuit issued an opinion regarding the final national ambient air quality standards for ozone and particulate matter.
Title 40, Part 50 of the Code of the Federal Regulations lists the ambient air quality standards for ozone.
An almost colorless, gaseous form of oxygen with an odor similar to weak chlorine. A relatively unstable compound of three atoms of oxygen, ozone constitutes--on the average--less than one part per million (ppm) of the gases in the atmosphere (peak ozone concentration in the stratosphere can get as high as 10 ppm). Yet ozone in the stratosphere absorbs nearly all of the biologically damaging solar ultraviolet radiation before it reaches the Earth's surface where it can cause skin cancer, cataracts, and immune deficiencies, and can harm crops and aquatic ecosystems. See ozone layer.
Ozone is produced naturally in the middle and upper stratosphere through dissociation of molecular oxygen by sunlight. In the absence of chemical species produced by human activity, a number of competing chemical reactions among naturally occurring species--primarily atomic oxygen, molecular oxygen, and oxides of hydrogen and nitrogen--maintains the proper ozone balance. In the present-day stratosphere, this natural balance has been altered, particularly by the introduction of man-made chlorofluorocarbons. If the ozone decreases, the ultraviolet radiation at the Earth's surface will increase. See greenhouse gas
Tropospheric ozone is a by-product of the photochemical (light-induced) processes associated with air pollution. See photochemical smog. Ozone in the troposphere can damage plants and humans.
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