Ozone (O3) exists in two distinct layers in the Earth's atmosphere and is considered "good" or "bad" depending on where it is. The US EPA has coined a maxim to help us remember: "good up high -- bad nearby."

The atmospheric layer where we live is known as the troposphere; it extends from the surface of the Earth up to about 6 miles (10 km). Ozone in this layer is a bad pollutant; vehicles, power plants and factories emit air pollution that forms ground level O3.

Ozone is a major component of urban smog and damages human health, vegetation, and many common materials such as rubber, cloth and paint. Although O3 concentrations on the Island of Hawai'i are generally very low, certain areas in urban Honolulu do occasionally exceed state health standards.

In contrast, "good" ozone resides in the stratosphere, the atmospheric layer that extends upward from about 6 to 30 miles (10-50 km). When traveling in a commercial jet, you are at the base of the stratosphere.

Stratospheric O3 is important for protecting life on earth by absorbing much of the harmful ultraviolet sunlight radiation known as UV-B. Increases in UV-B exposure can lead to more cases of skin cancer, cataracts, and impaired immune systems. Also, damage to UV-B sensitive crops, such as soybeans, and to marine organisms, could reduce food supplies.

Although ozone in the stratosphere is naturally produced and destroyed at a constant rate, humans are gradually tipping the balance by using ozone-depleting substances.

The chemicals used in refrigerators, air conditioners, fire extinguishers and solvents can reach the stratosphere, where they are broken down and release chlorine and bromine molecules that destroy "good" O3.

One chlorine or bromine molecule can destroy 100,000 ozone molecules, so O3 in the stratosphere is disappearing much faster than nature can replace it.

(Interestingly, explosive volcanoes contribute a minor amount of chlorine to the stratosphere -- about 3 percent of the total -- while humans contribute 82 percent. Gases from quieter eruptions, such as the current one at Kilauea, do not reach and affect stratospheric ozone.)

The Hawaiian Volcano Observatory (HVO), through a cooperative project with the National Park Service and US EPA, measures the column of O3 between the ground and the sun, as well as the amount of harmful UV-B getting through to the Earth's surface.

Data are collected using a sensitive spectrophotometer that carefully measures light of specific wavelengths. The HVO site is part of a nationwide network that is examining the effects of UV-B on the health of humans and other species.

The network also contributes to an international effort to track the global distribution of stratospheric O3 depletion. At HVO, this instrument also measures sulfur dioxide (SO2) and nitrogen dioxide (NO2), two gases that are released during and after lava is erupted.

The Earth's atmosphere is a fragile layer which protects life on earth from the damaging radiation from the sun. If the Earth were the size of soccer ball, then a layer of plastic food wrap around the ball would represent the troposphere, where we live.

The stratosphere, where the good O3 resides, would be an additional 4 layers of plastic wrap.

The good news is that there are things that we can all do to help keep the thin, fragile layers of our atmosphere healthy so that we too can remain healthy. To learn how you can help minimize the production of "bad" O3 and help protect the "good" stratospheric ozone layer, check out this website.

(This article was written by scientists at the U.S. Geological Survey's Hawaiian Volcano Observatory, who often prepare such articles for readers of their weekly Eruption Update. It has been reformatted and edited slightly for UniSci readers.)

05-Sep-2001