the solar radiation reaching the
upper stratosphere.

The mechanism for the production of ozone is the absorption by oxygen
molecules (O2) of relatively short-wavelength ultraviolet light. The
oxygen molecule separates into two atoms of free oxygen, which
immediately unite with other oxygen molecules on the surfaces of
particles in the upper atmosphere. It is this union which forms ozone,
or O3. The heat released by the ozone-forming process is the reason
for the curious increase with altitude of the temperature of the
stratosphere (the base of which is about 36,000 feet above the earth's
surface).

While the natural chemical reaction produces about 4,500 tons of ozone
per second in the stratosphere, this is offset by other natural
chemical reactions which break down the ozone. By far the most
significant involves nitric oxide (NO) which breaks ozone (O3) into
molecules. This effect was discovered only in the last few years in
studies of the environmental problems which might be encountered if
large fleets of supersonic transport aircraft operate routinely in the
lower stratosphere. According to a report by Dr. Harold S. Johnston,
University of California at Berkeley--prepared for the Department of
Transportation's Climatic Impact Assessment Program--it now appears
that the NO reaction is normally responsible for 50 to 70 percent of
the destruction of ozone.

In the natural environment, there is a variety of means for the
production of NO and its transport into the stratosphere. Soil
bacteria produce nitrous oxide (N2O) which enters the lower atmosphere
and slowly diffuses into the stratosphere, where it reacts with free
oxygen (O) to form two NO molecules. Another mechanism for NO
production in the lower atmosphere may be lightning discharges, and
while NO is quickly washed out of the lower atmosphere by rain, some of
it may reach the stratosphere. Additional amounts of NO are produced
directly in the stratosphere by cosmic rays from the sun and
interstellar sources.

It is because of this catalytic role which nitric oxide plays in the
destruction of ozone that it is important to consider the effects of
high-yield nuclear explosions on the ozone layer. The nuclear fireball
and the air entrained within it are subjected to great heat, followed
by relatively rapid cooling. These conditions are ideal for the
production of tremendous amounts of NO from the air. It has been
estimated that as much as 5,000