Ozone is a gas that forms in the atmosphere when 3 atoms of oxygen are combined (03). 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).
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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. 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. 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. 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. 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. High-Altitude "Good" Ozone
We live with ozone every day. It can
protect life on earth
For more information visit the
Stratospheric Ozone website at http://www.epa.gov/ozone
How Does the Depletion of "Good" Ozone
Affect Human Health and the Environment?
What is Being Done About the Depletion
of Good Ozone?
BAD NEARBY
What Causes "Bad" Ozone?
How Does "Bad" Ozone Affect Human Health
and the Environment?
What Can You
Do?
Ground-Level "Bad" Ozone
or harm it, but we have the power to
influence
ozone's impact by the way we live.
Also visit
EPA's Office of Air and Radiation website at http://www.epa.gov/oar/
