Ozone: The Facts
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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
Ozone is a form of oxygen with three atoms, instead of the usual two atoms. It is a photochemical oxidant and, at ground level, is the main component of smog. Ozone is not emitted directly into the air but is formed through chemical reactions between natural and man-made emissions of volatile organic compounds (VOCs) and nitrogen oxides in the presence of sunlight. These gaseous compounds mix like a thin soup in the ambient, or outdoor, air, and when they interact with sunlight, ozone is formed. Sources of these pollutants include automobiles, gas-powered motors, refineries, chemical manufacturing plants, solvents used in dry cleaners and paint shops, and wherever natural gas, gasoline, diesel fuel, kerosene, and oil are combusted. Ozone pollution is the periodic increase in the concentration of ozone in the ambient air, the natural air that surrounds us. It is mainly a daytime problem during summer months because warm temperatures play a role in its formation. When temperatures are high, sunshine is strong, and winds are weak, ozone can accumulate to unhealthful levels. Ground-level ozone is the most prevalent air
pollutant in Texas and the nation. Ozone is often one of several pollutants that make up
"smog," which you may recognize as the reddish-brown haze that forms when air
quality is particularly poor. But because ozone itself is colorless, the air can look
clear even when high ozone concentrations are present.
Stratospheric ozone
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.
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:
VOCs include many organic chemicals that vaporize easily, such as those found in gasoline and solvents. They are emitted from many sources, including:
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. Why are People Concerned?The extent of the problemOzone 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:
Return to "Why are People Concerned?" The damage doneThe biggest concern with high ozone concentrations is the damage it causes to human health and vegetation. High concentrations of ozone can cause:
Return to "Why are People Concerned?" Who can suffer the affectsChildren 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. Return to "Why are People Concerned?" The financial tollAir 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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