What Are the Harmful Effects of Ozone at Ground Level?

Ozone occurs naturally in the stratosphere, six to eight miles above the earth, where it protects the Earth from harmful ultraviolet B rays. Ozone should be rare in the troposphere, the layer extending six miles from the surface, but the Environmental Protection Agency warns that industrial and auto emissions of volatile organic compounds have created dangerous amounts of ozone in the troposphere. This ground-level ozone causes health problems in humans, creates smog, reduces crop yields and damages vegetation. The Clean Air Act charges the EPA with promoting programs to reduce emissions and reduce the amount of ground-level ozone.

Damages Forests and Vegetation

• Plants damaged by ozone are unable to resist disease and pests.

  Ozone penetrates plant leaves and oxidizes tissue causing damage. The growth of the plant is stunted and its ability carry out photosynthesis is reduced. The plant will produce less oxygen to return to the air and less food for itself. This type of damage occurs where ozone exceeds levels safe for vegetation, so the damage often affects city parks and greenways, as well as national parks, forests and recreational areas. Ground-level ozone concentrations and affected green areas are tracked by NASA's Ozone Mapping Instrument.

Ground-Level Ozone Damages Crops

• A five-year study shows reduced soybean yields due to ozone.

  The U.S. soybean crop is worth $27 billion per year. According to a five-year study by NASA and presented at the American Geophysical Union Joint Assembly meeting in May 2009, ground-level ozone damage to the U.S. soybean crop has reduced the yield by as much as 10 percent or $2 billion dollars. Ground-level ozone in midwestern farm country is a result of summer heat combined with stagnant air masses accelerating the chemical reactions between carbon monoxide, hydrocarbons and nitrogen oxide. These emissions are the result of fossil fuel burning.

Respiratory Problems in Humans

• Burning fossil fuels creates ground-level ozone.

  Ozone reacts strongly with living tissue and is toxic at high levels. Lung irritation and coughing occurs even when low amounts of ground-level ozone are inhaled. Breathing ozone results in throat irritation and congestion. For those already suffering from lung diseases such as bronchitis, emphysema and asthma, ozone will aggravate those conditions. Long-term exposure to ozone may result in scarred lung tissue. Because ground-level ozone forms in higher concentrations outdoors in warm weather, children and outdoor workers are especially at risk. Researchers at NASA estimate that 4,000 deaths per year may be attributed to high ozone levels in the summer.

Climate Change

• Ground-level ozone may contribute to global warming.

  Fossil fuel emissions resulting in increased ground-level ozone concentrations have increased 25 percent since the early 20th century. This may contribute to climate change, resulting in longer periods of drought and more severe droughts. According to the Intergovernmental Panel on Climate Change, researchers need to study this area some more as climate models are very complex.