The ozone near the earth's surface is the result of photochemical reactions.
When too much ozone is produced at the surface and is mixed with other gases
and particles it forms what we know as smog. Clean surface air contains little
ozone; however, burning fuels by cars, factories and other sources increase
the ground level ozone, making breathing difficult and irritating eyes. Even
though ozone is toxic to humans and animals, it is an excellent sterilizer.
In fact, ozone is used as an oxidant to remove harmful bacteria and bad odors
from food and water
The stratospheric ozone is approximately 10-25 miles above the earth's surface
in the upper atmosphere (stratosphere). It forms when the sun reacts with natural
nitrogen compounds. Stratospheric ozone provides a permanent filter of the sun's
UVC rays but absorbs only some of its UVB rays and none of its UVA rays.
What affects the Ozone layer's effectiveness?
Time of day.
When the sun is highest in the sky, UV rays have the least distance to travel
through the ozone layer and the rest of the atmosphere and are therefore more
intense. It is particularly important to limit direct exposure to the sun during
midday, when UV levels are at their peak.
Time of year.
The sun's angle varies with the seasons - highest in summer, lower in winter.
UV radiation levels reaching the Earth's surface tend to be highest in the summer,
intermediate in spring and fall and lowest in winter. UV overexposure can occur
in the winter, however, where there is snow or ice, both of which reflect a
high percentage of UV rays.
The further away from the equator one travels, the lower the sun's angle in
the sky. This is why higher latitudes typically receive less UV radiation than
UV intensity increases significantly with altitude because there is less atmosphere
available to absorb the damaging rays. The combination of higher UV levels,
reflective snow, and high winds make mountain climbing particularly hard on
the skin. Special care should be taken to prevent UV exposure at high altitudes.
Cloud cover generally reduces UV levels, but to varying degrees. Low, thick
stratus clouds block the most UV radiation. High, wispy cirrus clouds let most
UV through. Certain weather conditions allow puffy, scattered cumulus clouds
to increase UV radiation through reflection from the sides of the clouds.
The Ozone Hole
Artificial chemicals (chlorofluorocarbons "CFC's"), such as dry-cleaning
and refrigeration chemicals, byproducts of manufacturing processes and nitrogen
fertilizers, are diminishing the ozone layer. The ozone hole is presently roughly
the size of Europe and is located over Antarctica. The hole reaches its minimum
concentrations around October of each year. Scientists suspect that the ozone
layer's location is related to the isolation of CFC's over Antarctica by the
Southern Hemisphere polar vortex.
There is an obvious correlation between the diminished ozone layer and rising
skin cancer rates. Skin cancer rates are increasing far more rapidly in the
far northern and far southern latitudes where the ozone depletion is greatest.
Several International Conventions on the Protection of the ozone layer have
produced agreements (Montreal Protocol) by 93 nations to phase out CFC's. Even
so, their presence in the atmosphere is expected to double in the next few decades
because the agreements allow these countries to continue to process CFC's for
a time in order to lessen the impact to the world economy. Also, CFC's released
in the '90's will continue to linger for years. Nevertheless, it is hoped that
the ozone layer will recover completely by the year 2060. More recently, another
area of reduced ozone was discovered over the Northern Hemisphere, presenting
a more dangerous threat to human life as this area is more heavily populated