The OZONE

Ground Level Ozone

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

Stratospheric Ozone

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.

Latitude.
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 equatorial regions.

Altitude.
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.

Weather conditions.
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 than Antarctica.