B. Ozone

More worrisome is the possible effect of nuclear explosions on ozone in the
stratosphere. Not until the 20th century was the unique and paradoxical
role of ozone fully recognized. On the other hand, in concentrations
greater than I part per million in the air we breathe, ozone is toxic; one
major American city, Los Angeles, has established a procedure for ozone
alerts and warnings. On the other hand, ozone is a critically important
feature of the stratosphere from the standpoint of maintaining life on the
earth.

The reason is that while oxygen and nitrogen in the upper reaches of the
atmosphere can block out solar ultraviolet photons with wavelengths shorter
than 2,420 angstroms (A), ozone is the only effective shield in the
atmosphere against solar ultraviolet radiation between 2,500 and 3,000 A in
wavelength. (See note 5.) Although ozone is extremely efficient at
filtering out solar ultraviolet in 2,500-3,OOO A region of the spectrum,
some does get through at the higher end of the spectrum. Ultraviolet rays
in the range of 2,800 to 3,200 A which cause sunburn, prematurely age human
skin and produce skin cancers. As early as 1840, arctic snow blindness was
attributed to solar ultraviolet; and we have since found that intense
ultraviolet radiation can inhibit photosynthesis in plants, stunt plant
growth, damage bacteria, fungi, higher plants, insects and annuals, and
produce genetic alterations.

Despite the important role ozone plays in assuring a liveable environment
at the earth's surface, the total quantity of ozone in the atmosphere is
quite small, only about 3 parts per million. Furthermore, ozone is not a
durable or static constituent of the atmosphere. It is constantly created,
destroyed, and recreated by natural processes, so that the amount of ozone