Oxygen not ozone protects earth from ultraviolet light

Thanks for your informative article on the upcoming Rio Conference.

I want to comment on your reference to the U.N.’s Achim Steiner and his statement that progress has been made on reducing products that damage ozone.

For purely commercial reasons that I won’t get into, there was a panic move to reduce chlorofluorocarbon (CFC) based products for fear that they were the cause of some ozone holes that were in our atmosphere.

Without sunlight ozone wouldn’t exist in our atmosphere. The chemistry is fairly simple. Molecular oxygen (O2) is converted to ozone (O3) in the presence of ultraviolet light and/or electrical discharges like lightning. Like most chemical reactions, equilibrium exists between oxygen converting to ozone in the presence of ultraviolet light and then ozone recombining to form oxygen in the absence of such light.

In other words ozone in our atmosphere is the result of ultraviolet light bombardment from the sun hitting our atmosphere. Any areas without ozone are due to either darkness or insufficient light contacting our oxygen.

The highest concentrations of ozone exist over our tropics and subtropics where sunlight is most direct or incident. At the two polar regions ozone is not formed, since the sunlight is weak and enters obliquely, leaving two rather large holes. By the way these holes were reported by British scientists as early as 1957, long before major use of CFC’s. As the sun moves north during our summer, the northern hole shrinks in size while the southern hole increases in size and vice versa during our winter.
An interesting example would be our moon. Due to its orbit and rotation it always shows its same side to the sun. If the moon were to have an oxygen atmosphere like ours, it could be expected to have large ozone concentrations on its sunny side and none on its dark side.

In summary, the presence of ozone indicates that our oxygen has absorbed damaging ultraviolet light from the sun not the reverse. Ozone is not a major ultraviolet light absorber. It’s the oxygen that absorbs and reduces the ultraviolet light to protect us.

We underwent major economic dislocations converting from Freon 12 to so called, safer CFC’s without considering the chemistry involved. Let’s hope we do a better job with respect to the causes of climate change.
Clifford Dukes
La Aurora de Heredia

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