Ultraviolet Radiation

Characteristics of Ultraviolet Radiation

UV rays are just beyond visible light at shorter wavelengths than the last visible ray, which is violet. Ultraviolet rays are part of the electromagnetic spectrum that can reach a high enough level on earth to be harmful to plants, animals and humans.

http://nas.nasa.gov/About/Education/Ozone/radiation.html

The amount of UV radiation reaching the earth varies depending on the directness of the sun’s rays, time of day, time of year, the location’s latitude, cloud cover, and the amount of dust, haze and pollution in the air.

Wavelength

There are three categories of UV radiation: UV-A, UV-B and UV-C. UV-A rays have a wavelength of 320-420 nanometers (nm). UV-B rays have a wavelength of 280-320 nm, and UV-C rays have a wavelength of less than 280 nm.

Effects of UV Radiation

UV-C radiation is filtered out by ozone in the stratosphere. Only a small amount reaches the earth’s surface.

UV-B radiation poses a threat to life on earth even though some of it is filtered out by ozone in the stratosphere. UV-B radiation is capable of causing harm at the molecular level. The cumulative exposure of UV-B radiation may cause sunburn, cataracts, suppressed immune systems, premature aging including; wrinkles and skin discolorations as well as skin cancer.

The most common areas of the body to develop skin cancer are on the face or neck, ears, forearms or hands. There are three main types of skin cancer; basal cell carcinoma, squamous cell carcinoma, and malignant melanomas.

ABCDs of Melanoma

Asymmetry: One half of the growth doesn't match the other half.
Border irregularity: The edges of the growth are ragged, notched, or blurred.
Color: The pigmentation of the growth is not uniform. Shades of tan, brown, and black are present. Dashes of red, white, and blue also may appear.
Diameter: Any growth greater than 6 millimeters (about the size of a pencil eraser) is cause for concern. http://www.epa.gov/sunwise/stayheal.html

UV-A radiation causes us less harm compared to the shorter wavelengths. Although, it can cause sunburn and cataracts. UV-A radiation can benefit humans by synthesizing vitamin D in the body.

Protection from UV Radiation

UV radiation levels are highest at the middle of the day. Clouds and ozone have an affect on UV levels, but are not significant enough protection. Humans can protect themselves by avoiding exposure to the sun around noon, wearing sunscreen and sunglasses with UV protection.

Facts and Figures

• There has been an 1,800 percent rise in malignant melanoma since 1930.
• One American dies of skin cancer every hour.
• One in five Americans develops skin cancer.
• People get 80 percent of their lifetime sun exposure by the age of 18.
  http://www.epa.gov/sunwise/stayheal.html
  

References

http://www.epa.gov
http://www.nasa.gov/home/index.html