Ozone pollution is the most wide-spread air quality problem in the
United States. This page explains what ozone is and why it is
harmful.
What is Ozone?
Ozone is a gas that is formed in the atmosphere when three atoms
of oxygen combine. Naturally occurring ozone is found high in the
stratosphere surrounding the earth and in ground-level ambient
air.
Stratospheric ozone forms high in the atmosphere
when intense sunlight causes oxygen molecules (O2) to break up and
re-form as ozone molecules (O3). Popularly called "good ozone," it
shields people, trees, crops, property, and microorganisms from the
harmful effects of the sun's ultraviolet light.
One way that ozone forms low in the atmosphere, at ground level,
is when certain substances emitted by trees and other vegetation,
soil microorganisms, and lightning react together to form low,
background concentrations of ozone.
If ground-level ozone were produced only from
natural sources of emissions, it would be of no concern. Both
animal and plant life tolerate natural background concentrations of
ozone.
But many contemporary human activities result in emissions of
additional chemical compounds, called precursors, that also react
in the air to form ozone or "bad ozone" and other harmful
gases.
These activities include transportation, energy production and
some industrial and commercial operations.
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How Does Ozone Occur?
Ozone pollution is a key component of smog. It is mainly a
daytime problem during the summer months. Strong sunlight and hot
weather causes ground level ozone to form in harmful concentrations
in the air.
Ozone is not emitted directly into the air. Instead it is formed
in sunlight, which initiates a series of complex atmospheric
chemical reactions. These reactions primarily involve nitrogen
oxide (NOx) and volatile organic compound (VOC) emissions, called
precursors.
At ground level, ozone can harm plants and other materials
through a process called oxidation. For these reasons, ozone is
called a photochemical oxidant.
NOx is produced almost entirely as a by-product of
high-temperature combustion.
Common sources of NOx include:
- automobiles, trucks, and marine vessels
- construction equipment
- power generation
- industrial processes
- natural gas furnaces
VOCs include many organic chemicals that vaporize easily, such
as those found in gasoline and solvents. They are emitted from many
sources, including:
- gasoline stations
- motor vehicles, airplanes, trains, boats
- petroleum storage tanks
- oil refineries
In addition, biogenic, or natural emissions from trees and
plants, are a major source of VOCs.
The concentration of ozone in the air is determined not only by
the amounts of ozone precursor chemicals, but also by weather and
climate factors. Intense sunlight, warm temperatures, stagnant
high-pressure weather systems, and low wind speeds cause ozone to
accumulate in harmful amounts.
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Why are People
Concerned?
The extent of the problem
Ozone pollution near the ground is the most wide-spread air
quality problem in the United States. The public in nearly 100
major cities is periodically exposed to harmful concentrations of
ozone.
In Texas, four urban areas do not meet federal standards for ozone.
These areas are home to nearly 50 percent of our state's
population:
- Houston-Galveston
- Dallas-Fort Worth
- Beaumont-Port Arthur
- El Paso
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The damage done
The biggest concern with high ozone concentrations is the damage
it causes to human health and vegetation.
High concentrations of ozone can cause:
- shortness of breath
- coughing or wheezing
- headaches
- nausea
- throat and lung irritation
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Who Can Be Affected?
Children
Children often play outside for long periods during the summer.
Their lungs are still developing, and they breathe more rapidly and
inhale more air pollution per pound of body weight than adults. On
days when ozone levels are high, these factors put children at
increased risk for respiratory problems.
People with lung diseases
People who suffer from lung diseases like bronchitis, pneumonia,
emphysema, asthma, and colds have even more trouble breathing when
the air is polluted. The effects can be worse for anyone who spends
significant periods of time exercising or working outdoors.
Active adults
During exercise or strenuous work we breathe more often and draw
air more deeply into the lungs. When we exercise heavily, we may
increase our intake of air by as much as 10 times our level at
rest.
The interaction between air pollution and exercise is so strong
that health scientists typically use exercising volunteers in their
research.
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The financial toll
Air pollution is costly. The costs include expenses for
increased health care and property damage decreased property values
and diminished quality of life.
Reducing air pollution also is costly. The costs can include
expenditures for installing, operating, maintaining, and monitoring
emission control systems.
Some of these costs are paid directly by business and industry.
Others are paid indirectly through increased production costs and
loss of business and economic opportunity.
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