Tropospheric Ozone = Low Ozone = Bad Ozone

EEK! - Our Earth - Ozone Action For Children: Good Ozone, Bad Ozone
How ground-level ozone affects plants and animals (including you!)

Wisconsin Department of Natural Resources

The atmosphere of the Earth is divided into layers. Each layer is a little different. Stratospheric ozone is found in the stratosphere, a layer of air way up in the atmosphere. The stratosphere is between 8 and 30 miles above the ground - too far away for you to breathe any of its air! The ozone in this layer of air protects plants, animals, and us by blocking the most harmful rays of the sun.

Tropospheric ozone, (ground-level ozone) is found in the troposphere, which is the layer of air closest to the Earth's surface. The troposphere is the air from the ground to about 8 miles up into the atmosphere - it's the air we breathe. Ozone does not naturally occur at harmful levels in the troposphere. Our ground-level ozone problems are caused by human activities. Read "Hot Summer Days" to learn how humans cause "bad ozone."

You may have heard that ozone shields us from the sun's harmful UV, or ultraviolet, rays. This type of ozone is called "stratospheric" ozone. Stratospheric ozone is made up of three oxygen atoms, and has no color, no taste, and not much odor. Stratospheric ozone is the same chemical as ground level ozone. So what's the difference?

The difference between stratospheric ozone and ground level ozone, (tropospheric ozone) is where each is found. One is up high, one is nearby.

Just remember: "Good up high, bad nearby!" You might wonder: we have too much ozone in the troposphere and not enough in the stratosphere why can't we just send tropospheric ozone up into the stratosphere? Unfortunately, we can't simply 'pump' our extra ozone into the stratosphere. So, to keep it from causing problems down here in the troposphere, we have to stop it from forming in the first place.

Ground-level ozone is unstable. It reacts chemically with plants, rubber, and the tissues of living creatures - including you. In fact, kids and elderly people are affected the most.

Ozone has no color, no taste, and not much odor. It may sound harmless, but it has the ability to irritate your lungs or break down your lung tissues. Do you have asthma or do you know someone who does? Ozone can cause an asthma attack, and it can make asthma attacks worse than usual. Even people who don't have asthma can have trouble breathing on days with high levels of ground-level ozone, especially people who spend a lot of time outdoors. Even though we can't see it, scientists know ground-level ozone exists. They can measure it using special instruments that detect what's in the air we breathe.

Ground-level ozone can also damage the leaves of plants and trees. Some plants affected include soybeans, clover, onions, spinach, alfalfa, and milkweed. Trees such as lilac, aspen, ash, and white pine are also injured by ground-level ozone. Ground-level ozone can cause the leaves to fall off these plants, prevent the plants from growing very big, or even cause the plants to die. Then the humans, animals, and insects - like the monarch butterfly that depend on these plants may not have as much food or shelter. In California ozone damage has been shown to have a serious impact on the entire ecosystem. In Wisconsin the effect has been smaller, but ozone still has an effect - for example, high levels of ozone have destroyed 10 - 20 percent of some crops.

Negative Impacts of Tropospheric Ozone
The University Corporation for Atmospheric Research & the National Center for Atmospheric Research

While stratospheric ozone shields us from ultraviolet radiation, in the troposphere this irritating, reactive molecule damages forests and crops; destroys nylon, rubber, and other materials; and injures or destroys living tissue. It is a particular threat to people who exercise outdoors or who already have respiratory problems.

Ozone affects plants in several ways. High concentrations of ozone cause plants to close their stomata. These are the cells on the underside of the plant that allow carbon dioxide and water to diffuse into the plant tissue. This slows down photosynthesis and plant growth. Ozone may also enter the plants through the stomata and directly damage internal cells.

plants hurt by ozone

Reduction of soil carbon formation by tropospheric ozone under increased carbon dioxide levels
Nature, 2003

In the Northern Hemisphere, ozone levels in the troposphere have increased by 35 per cent over the past century1, with detrimental impacts on forest2, 3 and agricultural4 productivity, even when forest productivity has been stimulated by increased carbon dioxide levels5.

The Impact of Tropospheric Ozone Pollution on Plants
Penn State University
University Park, PA

Tropospheric ozone also is one of the most significant and damaging airborne pollutants to plant life. Therefore, it is known as a powerful "phytotoxin." Symptoms of plant damage can appear as early as one day after high exposure of several hours. Noticeable effects to the leaves of crops include changes in shape, discoloration and necrosis (i.e., cell death). More subtle effects include reductions in plant size and weight, due to the fact that ozone pollution can decrease a plant's ability to perfom photosynthesis. Ozone pollution also takes its toll on forests. Increased concentrations of ozone pollution are the primary cause of the decline in pines in southern California and the eastern United States. Ozone pollution has also been considered as the primary cause of many declining European forests.

State studies show rising ozone levels threaten trees, crops
The Capital Times, Madison, WI, Anita Weier 6/11/2008

People have a hard time breathing when ozone levels are high.

So do plants.

"It is very similar to people with asthma," said David Karnosky, a forestry professor at Michigan Tech University in charge of a long-running experiment near Rhinelander in northern Wisconsin where some trees get extra doses of ozone and others do not.

"This is the canary in the coal mine," Karnosky warned, explaining that the levels of ozone the trees in the experiment are experiencing are comparable to the levels that could exist in northern Wisconsin by 2050.

If that happens, the consequences are potentially serious for both plants and people....

Trees that got those extra shots of ozone have only three-fourths as much growth and yield as those that did not receive the pollutant, Karnosky said.

"It knocks your eyes right out," Sharkey added.

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Northern Hardwoods Dying in WV, PA
Appalachian Voice, 2001

The northern hardwood forests of the Allegheny and Monongahela National Forests and surrounding private lands are dying in record numbers, according to a recent air survey of the region.

The survey, conducted by two environmental groups, show that tens of thousands of acres of sugar maples, yellow birch, beech, black cherry, red oaks and several other species are all dying at once over the higher elevations of the mountains of eastern West Virginia and northwest Pennsylvania.

The scope of the decline also extends to the lower elevations of the Appalachian region into the oak-hickory and mixed-mesophytic forests so prominent in southern West Virginia and south, said survey director Dr. Harvard Ayers, a professor at Appalachian State University in Boone, NC.

Northern hardwood forests span the length of the Appalachian Mountains from New England to the Great Smoky Mountains of Tennessee and North Carolina. The ten or so species that comprise these mountain hardwoods occupy the life zone just under the boreal forests that are dominated by the red spruce and the Fraser and balsam firs.

Together, these dozen or so mountain tree species are bearing the brunt of air pollution impacts from coal-fired power plants and (to a lesser degree) cars and trucks, which have made the central and southern Appalachians the most polluted skies in the country. Leaf-killing ozone in these mountains is frequently twice what it is in the surrounding lowlands.

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Tropospheric Ozone in the Mediterranean Basin: Evidence of its Effects
Recognizing Ozone Effects to Vegetation in a Simple Way

International Society of Environmental Botanists, Vol. 10 No. 2 - April 2004

Photo-oxidants, and especially ozone, have been widely regarded as harmful to vegetation since the 80s, although in the 60s its effects were already detected in California. However, it is during the last decade when ozone become an issue of concern in Europe. Ozone pollution, unlike fluoride or sulphur dioxide, does not leave elemental residue that can be detected by means of analytical techniques in vegetative tissues. Thus, ozone injury in leaves, are the only evidence easily detected in the field. So far, experimental studies have focused mainly on explaining the mechanisms that produce damage, rather than to identify and characterise symptoms observed in the field at a regional scale. Recent researches have increased our knowledge on the subjacent mechanisms that explain the effects of ozone on crops, and to a lesser extent, on trees and other wild plants. A long term effect of this pollutant on forests may affect some of their functions, e.g. their role in water and energy balances, protection against soil erosion, cover of vegetation, and aesthetics of the landscape. One possible effect on plant communities might be the change in species composition and loss of biodiversity, an important potential threat when regions with many endemic plants are considered. Furthermore, before these problems are approached, more basic and detailed studies on the sensitivity of the species under different environmental conditions, including e.g. nutritional aspects, have to be undertaken.

Excess Ozone Chokes Plants, Accelerates Global Warming

"Ozone could be twice as important as we previously thought as a driver of climate change," said study co-author Peter Cox.

Scientists have long known that ozone is a greenhouse gas, trapping radiation within the atmosphere and leading to rising global temperatures. But the new study suggests that ozone may have a much more significant climate impact by adversely affecting plants' ability to remove carbon dioxide from the atmosphere.

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