Ozone: "Good up high, bad nearby"

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.

How ground-level ozone affects plants and animals (including you!)

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.