How Ground-level Ozone Affects the Way We Live and
Breathe
Published by the US EPA
Office of Air Quality Planning & Standards
November 2000
Ground-level ozone is an air pollutant that causes human health
problems, and damages crops and other vegetation, and it is a key ingredient
of urban smog.
![traffic photo [courtesy of EPA - Environmental Protection Agency]](images/traffic.jpg) Table
of Contents
Ground-level
Ozone: What is it? Where does it come from?
Chief Causes
for Concern
Health and
Environmental Impacts of Ground-level Ozone
Ozone (O3) is a gas composed of three oxygen atoms.
It is not usually 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 heat and
sunlight. Ozone has the same chemical structure whether it occurs miles
above the earth or at ground level and can be "good" or "bad," depending
on its location in the atmosphere. "Good" ozone occurs naturally in the
stratosphere approximately 10 to 30 miles above the earth's surface and
forms a layer that protects life on earth from the sun's harmful rays. In
the earth's lower atmosphere, ground-level ozone is considered "bad."
VOC + NOx + Heat +
Sunlight = Ozone
Motor vehicle exhaust and industrial emissions, gasoline vapors, and
chemical solvents are some of the major sources of NOx and VOC,
that help to form ozone. Sunlight and hot weather cause ground-level
ozone to form in harmful concentrations in the air. As a result, it is
known as a summertime air pollutant. Many urban areas tend to have high
levels of "bad" ozone, but even rural areas are also subject to increased
ozone levels because wind carries ozone and pollutants that form it
hundreds of miles away from their original sources.
Ground-level Ozone
- Triggers a variety of health problems even at very low levels
- May cause permanent lung damage after long-term exposure
- Damages plants and ecosystems
The summertime pollutant
Peak ozone levels typically occur during hot,
dry, stagnant summertime conditions. The length of the ozone season
varies from one area of the United States to another. Southern and
Southwestern states may have an ozone season that lasts nearly the entire
year.
Ozone can be transported over long distances
Ozone and the chemicals that react to form it can be carried hundreds
of miles from their origins, causing air pollution over wide regions.
Millions of Americans live in areas where ozone levels exceed EPA's
health-based air quality standards, primarily in parts of the Northeast,
the Lake Michigan area, parts of the Southeast, southeastern Texas, and
parts of California.
![ozone transport figure [courtesy of EPA - Environmental Protection Agency]](images/newozone.gif)
Ozone and the pollutants that form it can cause air quality problems
hundreds of miles away.
Ground-level ozone even at low levels can
adversely affect everyone. It can also have detrimental effects on
plants and ecosystems.
![lungs [courtesy of: EPA - Environmental Protection Agency]](images/lungs.jpg) |
Health Problems
- Ozone can irritate lung airways and cause inflammation
much like a sunburn, and other symptoms include wheezing,
coughing, pain when taking a deep breath, and breathing
difficulties during exercise or outdoor activities. People
with respiratory problems are most vulnerable, but even
healthy people that are active outdoors can be affected when
ozone levels are high.
- Repeated exposure to ozone pollution for several months
may cause permanent lung damage. Anyone who spends time
outdoors in the summer is at risk, particularly children and
other people who are active outdoors..
- Even at very low levels, ground-level ozone triggers a
variety of health problems including aggravated asthma,
reduced lung capacity, and increased susceptibility to
respiratory illnesses like pneumonia and bronchitis.
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![plant [courtesy of: EPA - Environmental Protection Agency]](images/plant.jpg) |
Plant and Ecosystem
Damage
- Ground-level ozone interferes with the ability of plants
to produce and store food, which makes them more susceptible
to disease, insects, other pollutants, and harsh weather.
- Ozone damages the leaves of trees and other plants,
ruining the appearance of cities, national parks, and
recreation areas.
- Ozone reduces crop and forest yields and increases plant
vulnerability to disease, pests, and harsh weather.
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Reference:
http://www.epa.gov/air/urbanair/ozone/index.html |
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[Nitrogen Oxide] [Ozone]
[Particulate Matter] [Sulfur
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