EPA’s New Ozone Rule Part 2

Recently, the Obama administration withdrew a proposal to reduce the maximum allowable level of ground-level ozone concentration in the atmosphere1. The question that I wish to address is whether the benefits that might accrue to our nation from such a reduction are greater than the costs, particularly to industry. To analyze this problem, we need to understand what ground-level ozone is, how it is formed, what man-made processes promote ozone formation, and what industry must do to reduce the level of ozone.

Ozone is a form (called an allotrope2) of oxygen, the eighth element in the chemical periodic table3. Pure oxygen usually exists as molecules consisting of two oxygen atoms each, represented by the chemical formula O2. Ozone consists of molecules of three oxygen atoms each, represented by the chemical formula O3. Despite the fact that ozone consists of nothing but oxygen atoms, it is far more chemically reactive than ordinary oxygen4. For example, one cannot breathe pure ozone: breathing ozone in concentrations fifty parts per million or higher is probably fatal within 60 minutes5. Likewise, ozone can dissolve far more readily in water than ordinary oxygen6 and attacks substances (such as certain rubbers) that are not touched by ordinary oxygen7.

Breathing ozone is harmful to health even in low concentrations. Breathing air with 1.5 parts per million (ppm) of ozone for more than two hours can result in severe lung irritation with fluid-buildup, chest pain and cough, and extreme fatigue5. Ozone is known to attack and injure the tissues in the upper respiratory system, although the damage can be repaired by the body in a matter of weeks8.

It is important to distinguish between ozone in the troposphere (that part of the atmosphere that rests on the surface of the Earth) and the stratosphere (that layer of the atmosphere between about 6 and 31 miles above the surface at temperate latitudes). About 90% of all ozone in the atmosphere is in the stratosphere where it performs the very important function of absorbing high-energy ultraviolet radiation from the sun (all of the UV-c rays, most of the UV-b rays, and about half of the UV-a rays)9, preventing them from reaching the surface of the Earth where they would harm life. This ozone poses no dangers to humans; on the contrary, it helps make life possible. It is the 10% of the ozone in the atmosphere that exists in the troposphere (called tropospheric or ground-level ozone) that poses problems and is the subject of the proposed government regulation.

According to NASA, ground-level ozone levels without the presence of human activity should be about 10 to 15 parts per billion (ppb, one part per million equals 1000 ppb)10. Industrial activity has boosted those levels significantly such that the Environmental Protection Agency has established a limit of 80 ppb10. It appears to me that most people are able to breathe in that level of ozone without ill effects, or respiratory illnesses would be much more common than they are now. The question is whether people with respiratory problems, the very young, and the very old are adversely affected. If they are, is it cost effective to lower levels of ozone to improve their quality of life? Also, could long-term exposure to 80 ppb of ozone cause any significant health effects?

In my next post, I want to discuss how ozone is produced.


  1. Statement by the President on the Ozone National Ambient Air Qualities Standards. White House website. To view, click here.
  2. For a good explanation of allotropes, see the Diffen website, Oxygen vs Ozone.
  3. See the WebElements Periodic Table on oxygen.
  4. Rachel Cassiday and Regina Frey, Washington University.Chemical Properties of Ozone. To view, click here.
  5. Ozone Levels and Their Effects, edited by Den Rasplicka, OzoneLab Instruments website. To view, click here.
  6. Bruce Mattson, Janel Michels, Stephanie Gallagos, Creighton Univerisity.Microscale Gas Chemistry, Part 28 Mini-Ozone Generator: 800 nanomoles/minute p.7 paragraph “Office Paper.” To view, click here.
  7. Bassam Z. Shakhashiri, University of Wisconsin – Madison.Chemical of the Week: Ozone paragraph 7. To view, click here.
  8. U.S. Environmental Protection Agency website, Ground-Level Ozone: Health. To view, click here. For a more detailed treatment, see Health Effects of Ozone in the General Population, which you can view by clicking here.
  9. U.S. National Aeronautics and Space Administration Ozone Hole website, Ozone Facts tab, paragraph 2. To view, click here.
  10. Jeannie Allen, The Ozone We Breathe, NASA Earth Observatory website. To view, click here.

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