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Name: Igor L.
Status: educator
Age: 60s
Location: N/A
Country: N/A
Date: 2001


Question:
Is there any real connection between stratospheric ozone and ground level one? I mean connection in trends. Now we have negative trend in column ozone. What trend should be in ground ozone from the theoretical point of view?


Replies:
Ground-level ozone is a photochemical reaction product of air oxygen, nitrogen oxide catalysts, and hydrocarbons. The nitrogen oxides and hydrocarbons are predominantly provided by human activity, specifically car and diesel exhaust. Stratospheric ("ozone layer") ozone is also a photochemical reaction product, but its creation does not require hydrocarbons or man-made nitrogen oxides. (The nitrogen oxides in the stratosphere occur naturally.) The increased destruction of stratospheric ozone observed recently is attributed to volatile man-made chlorine-containing compounds that rise to the stratosphere.

So increased ground-level ozone and decreased stratospheric ozone are both effects of man-made pollution. Different pollutants lead to the two different effects. The different ozone levels are connected to the extent that the pollutant trends are connected.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation


Igor,

Under some meteorological conditions, such as thunderstorm convection, which displaces much air vertically, down as well as up, ozone from the stratosphere can be brought to the surface. However, virtually all of the ozone near the surface is created photo-chemically, aided by man's pollution. The only other strong connection between the upper and lower parts of the atmosphere are the CFCs that are transported slowly into the stratosphere where they cause ozone depletion, as is easily seen over Antarctica (because of it's unique weather patterns).

Because of the effects of pollution, ozone had been increasing near the surface, while ozone depletion was taking place in the stratosphere. The increasing trend near the surface has been reversed in the past 10 years in the USA as a result of emission controls that have reduced ozone "precursors" like nitrogen oxides. Most of the "non-attainment" areas (where ozone was higher than EPA standards) have met the standards recently. More effective controls on power plant emissions that are presently being implemented will continue to help in this effort. Further reductions through cleaner automobiles and more efficient home heating would help even more, although it will be quite costly. All of this is wonderful for our country, but most of the world does not share our enthusiasm for and dedication towards cleaning the environment. The rest of the world needs to get on the bandwagon for future improvements to occur globally.

David R. Cook
Atmospheric Research Section
Environmental Research Division
Argonne National Laboratory


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