Watch out for That Sun

Ultraviolet radiation (UV) is, at least to humans, an invisible part of sunlight. But as you well know from a sunny day at the beach, it's biologically very active. UV radiation can have severe effects on exposed skin and eyes, cause cancer, weaken immune systems, and affect plants, animals, and ecosystems.

One of the main biological impacts of UV radiation on plants is that it reduces their rate of photosynthesis, the process that plants use to trap carbon dioxide from the air to create sugars for food, releasing oxygen in the process. UV radiation with a short wavelength, called UV-B, is most effective at reducing the photosynthesis rate. This reduced photosynthesis rate can directly affect the plants' ability to grow. Because different species may vary in their sensitivity to UV radiation, this may eventually affect biodiversity and change the structure of an ecosystem.

Although UV radiation has always been present throughout the evolution of earth and life, research is showing that we are now exposed to higher levels of UV because of the thinning of the ozone layer. The ozone layer, a concentration of ozone molecules in the stratosphere, protects us from UV by filtering the sun's radiation. Ozone molecules in this layer are constantly being produced and broken down, but chemicals like halons and chlorofluorocarbons (CFCs) that are used in refrigerators and air conditioners accelerate the breakdown of ozone. As a result, the ozone layer is getting thinner, allowing more UV to reach the earth's surface.

Found this perfect definition of Ultraviolet Radiation:

The UV radiation spectrum can be divided into three bands: UVA, UVB, and UVC.8 Little UVC radiation reaches the earth because it is filtered out by the ozone layer. 8 UVC does not cause a person to tan; however, it may cause some erythema of the skin. 8 UVB penetrates superficially into the epidermis and is the principal cause of sunburn reactions.4, 7 UVB is the wavelength that is mostly associated with inducing skin cancer. 8 UVB has been reported to be responsible for causing more than 90 percent of basal and squamous cell cancers. 4, 7, 9

In contrast to the effects caused by UVB, UVA is responsible for causing a slow natural tan to develop. 8 UVA radiation penetrate more deeply to the dermis of the skin, which can alter the fibers of the skin. 3 UVA may also contribute to the cancer-causing potential of UVB radiation. 3 Sunscreen lotions are more effective in protecting against shorter ultraviolet wavelengths (UVB) than against longer wavelengths (UVA). 10

Definition comes from http://www.medterms.com

References
1. Satcher, D. “Skin Cancer”. Centers for Disease Control and Prevention. National Skin Cancer Prevention Education Program. 1997. [available at www.cdc.gov]
2. Hurwitz S. “The Sun and Sunscreen Protection: Recommendations for Children.” J Dermatol Surg Oncol 14(6):657-660, 1988.
3. “Don’t Let the Sun Spot You.” Centers for Disease Control and Prevention. Last reviewed May 2003. [available at www.cdc.gov]
4. Nicol NH. “What’s New With Sunscreens? Choices-Choices-Choices.” Pediatr Nurs. 15(4):417-418, 1989.
5. Lewis RM, Fischer RG. “Sunscreen Agents.” Pediatr Nurs. 13(3):200-201, 1987.
6. Council on Scientific Affairs. “Harmful Effects of Ultraviolet Radiation.” JAMA. 262(3):380-384, 1989.