Clyde Burnett, Peak to Peak. Our atmospheric pressure and temperature decreases with altitude in the troposphere until at about 40,000 ft. It is a cold trap for the maximum altitude for water vapor and weather. At higher altitudes in the stratosphere, the temperature begins to increase with altitude due to absorption of much of the solar ultraviolet by the ozone layer. This is the “good” ozone that shields us from the damaging solar ultraviolet.

Tropospheric ozone is the “bad” ozone. We are warned that it will burn lung tissue, aggravating asthma and other respiratory problems. At these higher densities, it is also a greenhouse gas, absorbing in the Earth’s outgoing infrared.

Question:  We’ve heard about the Antarctic stratospheric ozone holes for years. Are they responsible for climate change?

Answer: The springtime Antarctic ozone holes have very little to do with the heat trapping of Earth’s infrared radiation in the greenhouse effect. The polar ozone holes were due to reactions of stable chlorine nitrate on polar stratospheric clouds. This released the catalytic compounds of chlorine that resulted in the subsequent springtime destruction of polar stratospheric ozone.

There is now an international agreement to cease production of these chlorine compounds for air conditioning systems, but the long atmospheric lifetime of this chlorine pollution will continue to make ozone holes for another 50 years or so. This should be a lesson for our control of the emission of long atmospheric lifetime CO2 greenhouse gas.

Question: I’ve heard that the tropospheric ozone increases from industrial pollution. Right?

Answer:  Yes. The chemistry that produces ozone in the troposphere is entirely different from the polar ozone hole chemistry. Tropospheric ozone is produced in the daytime atmospheric chemistry of precursor pollution molecules initiated by solar ultraviolet.

Some of the precursor molecules in the lower atmosphere are carbon monoxide and nitric oxide produced in energy generation for electricity and transport, along with numerous volatile organic compounds, some of which are produced in oil and gas production. The dependence on the presence of the precursor molecules generated by human activity and need for clear skies with strong solar ultraviolet makes its presence highly variable.

We are frequently warned on sunny summer days to avoid operating gas-powered lawn mowers or visiting gas stations to fill our gas tanks.

Question: How important is the health damage of this tropospheric ozone?

Answer:  Its production on sunny summer days is a danger especially for outdoor activity of children and elderly. Chemical reactions near the Earth’s surface on plants and other materials limit its lifetime to a few days.

Unfortunately the ozone destruction by plants is limited at high temperatures, so the combination of high temperatures and ozone pollution becomes a severe health threat.

Question: How important is its greenhouse effect?

Answer: It is less so than carbon dioxide or methane. Its importance is partly due to its absorption in the atmospheric window where other absorptions are absent.

Question: Is it getting worse? How can we control it?

Answer: We could have a prompt reduction in tropospheric ozone just by preventing the pollution of the precursor compounds. It would be especially valuable to stop the methane emissions from natural gas production activities, since methane is an even more damaging greenhouse gas.