Ozone & Your Health
What is Good v. Bad Ozone?
Ozone is a gas that forms when three atoms of oxygen are combined, but it is found in two
very different layers of the atmosphere. One is harmful to humans and the environment, the
other provides protection.
Troposphere
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 about 10 miles up, where it meets the second layer, the stratosphere.
Stratosphere
The stratospheric or "good" ozone layer extends upward from about 10 to 30 miles and shields us from the sun's harmful ultraviolet rays (UV-b) that can cause skin cancer.
What Causes the "Bad" Ozone Responsible for Ozone Alerts?
While humans are ultimately responsible for the production of bad ozone, it is not directly
released from human-made sources. Instead, it is a by-product of a chemical reaction. Ozone is
created at ground level when nitrogen oxides (NOx), volatile organic compounds (VOCs), and
sunlight are present. Hot weather heats up the reaction, accelerating the production of ozone.
That’s why we have ozone alerts during the warmest months of the year—April through October.
NOx + VOCs + Sunlight + Hot Weather = Ozone
Ozone concentrations can vary from year to year. Changing weather patterns, such as the number of hot, sunny days, periods of low winds, and other factors make long-term predictions difficult. While some VOCs come from natural sources, it is important to understand that most VOCs and NOx emissions come from human activities.
VOCs
We release VOCs into the air when we use appliances, lighting, lawnmowers, cars, and
paints and cleaning products containing VOCs. For example, industrial processes, motor vehicle
exhaust, gasoline vapors, and chemical solvents in paints and glues emit VOCs. They are almost
always composed of carbon and hydrogen. VOCs generally have a noticeable odor, but are nearly invisible and evaporate easily.
NOx
Nitrogen oxides form when fuel is burned at high temperatures, such as in the combustion process that powers a car. Humans produce NOx when they drive motor vehicles, use electric appliances that rely on utilities to burn coal or gas, and conduct other industrial and residential activities. According to the U.S. Environmental Protection Agency (U.S.EPA), 49 percent of NOx emissions come from motor vehicles. NOx emissions are particularly serious because they usually are odorless and colorless and can travel hundreds of miles.
Benzene and Toluene
Benzene and toluene are among the chemicals that may be found in products that release VOCs and NOx, especially paints and painting products, burned or stored fuels, cleaning products, and industrial solvents. Benzene is known to cause cancer, including leukemia. Toluene mainly affects the nervous system, causing cause headaches, confusion, and memory loss. Several studies have shown that unborn animals were harmed when their mothers breathed high levels of toluene. For more information on these chemicals, visit the Agency for
Toxic Substances & Disease Registry at www.atsdr.cdc.gov/ToxProfiles.
How Does Ozone Affect Peoples’ Health and the Environment?
Ozone and the chemicals that comprise it damage the natural environment. Moreover, ozone damages our bodies, sometimes permanently. The Journal of the American Medical Association recently found that long-term exposure to air pollution increases the risk of death from lung cancer, heart attack, stroke, asthma, emphysema, and chronic bronchitis. Even at low levels, it triggers a variety of health problems, including chest pains, coughing, nausea, throat irritation, and congestion. However, we do not yet know enough about how humans are affected by exposure to a combination of ozone and other chemicals that typically exist in our environment. We simply are not exposed to ozone alone; we are constantly taking in other chemicals through air, water, and food. This is an area scientists are beginning to study. Below are some of the problems we know ozone can cause.
Environmental
Ozone harms trees, plants, and animals. Ozone interferes with plants’ ability to produce and store food, compromising growth and reproduction. When weakened by ozone, plants are more susceptible to disease, pests, and environmental stresses. For example, ozone causes millions of dollars in damages per year to agricultural crops, according to California’s South Coast Air Quality Management District. NOx also can cause fish to die off in sensitive waterways.
Respiratory
Air pollution, including ozone, contributes to lung disease, which causes more than
350,000 deaths annually, making it the third-leading cause of death in the U.S. Ozone typically causes shortness of breath, chest pain when inhaling deeply (as with exercise), and wheezing or coughing. Moreover, repeated exposure to ozone pollution may permanently damage lungs. For example, when ozone impairs the lung’s ability to defend itself, respiratory infections are more likely. As a result, scientists are concerned that children who have more infections may be at greater risk of reduced lung function. Ozone also can reduce lung capacity and worsen bronchitis, emphysema, and asthma. NOx raises particular concerns because it contains tiny particles that can lodge deep in the lungs.
Cardiovascular
Ozone can worsen heart disease largely due to the presence of NOx.
Sensory
VOCs can irritate the eyes and nose, can cause headaches and nausea, and can damage the central nervous system. It also can cause dizziness and visual disorders and impair the memory.
Who is Most At Risk?
Anyone can be susceptible to ozone pollution. When the ozone level is particularly high, even healthy adults may notice any of the effects listed above. However children and seniors are most at risk to ozone, with 30 million citizens under age 14 and 17 million over 65. The U.S. EPA estimates that up to 20 percent of the U.S. population are especially susceptible to ozone—that’s about one person out of every five.
Children
Children spend more time outside exerting themselves while playing. As a result, they breathe in more air and breathe it in more deeply, causing pollution particles to lodge far into the lungs. Children also receive a larger dose of pollution than adults because their breathing rate is higher than adults, relative to their body weight and lung surface area. Moreover, they are also more sensitive to these high doses of chemicals as their bodies and brains are still developing and growing rapidly. Their narrower airways put them at greater risk of a blocked airway from irritation or inflammation caused by air pollution. An ongoing California study of children shows a connection between exposure to polluted air and reduced lung function. Studies also show that ozone exposure is a major factor in whether a child develops asthma.
People with Respiratory Problems
The U.S. EPA has found that people with chronic bronchitis, emphysema, and asthma are at risk from high ozone levels. Asthma has become more and more common in the U.S. As of 1998, asthma had affected about 26 million Americans at some point in their lives. Of these, 10.6 million, including 3.8 million children under age 18, had an asthma attack that year. An American Lung Association study found that on high-pollution days, children with asthma were 40 percent more likely to suffer attacks than on average-pollution days.
Seniors
Generally, though not always, seniors tend to be more at risk to the effects of ozone because their bodies may already be compromised by age or health problems, such as heart disease. It may simply be more difficult for their bodies to withstand the effects of ozone when they already may be working hard to address other health issues, such as high blood pressure. An ALA study found that as air pollution levels increased in the summer, daily emergency room visits by the elderly increased.
Other Sensitive Groups
People who exercise outdoors are also more susceptible to the effects of ozone. During exercise or exertion we breathe through our noses and mouths. When we breathe through the mouth, we inhale more pollution than if we only breathed through the nose, which helps to filter out pollution and particles. Ozone also makes people more sensitive to allergens, causing those who have allergies to suffer more during ozone season. Finally, some people healthy people are simply more sensitive to ozone than others.
Where ozone levels are often high, people’s initial symptoms may disappear over time.
However, this does not mean they have developed a resistance to ozone. Instead, ozone continues to cause lung damage even when the symptoms are gone.
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