Which Wavelengths are Harmful

Radiation need not be feared, but it must be respected. —Karl Morgan

Okay. So we know what the ozone layer is, why it is important, and that we have caused it serious harm. Have climate scientists observed any effects so far on the biological world, particularly on humans? The answer is a resounding yes. The most dramatic effect is a marked increase in skin cancer. To understand why, we first need to say a few words about the spectrum of ultraviolet light we receive from the sun (figure 8.1).

Radiation with wavelengths shorter than 0.01 micrometers is termed either gamma rays or X-rays. Radiation with wavelengths between 0.01 and 0.4 micrometers is called ultraviolet radiation and is further subdivided

Figure 8.1

Electromagnetic spectrum of solar radiation. Most of the energy occurs in the wavelengths of visible light and the invisible near-infrared. Vision in animals and photosynthesis in plants are adapted to these wavelengths.

Figure 8.1

Electromagnetic spectrum of solar radiation. Most of the energy occurs in the wavelengths of visible light and the invisible near-infrared. Vision in animals and photosynthesis in plants are adapted to these wavelengths.

o oo into UV-C, UV-B, and UV-A, with UV-C having the shortest wavelength and UV-A the longest. Like gamma rays and X-rays, ultraviolet rays are invisible to our eyes. Longer wavelengths, between 0.4 and 0.7 micrometers, are the ones our eyes are programmed to see as colors. Radiation with wavelengths longer than 0.7 micrometers is termed either infrared, microwave, or radio and TV waves, depending on wavelength. Our eyes cannot see these wavelengths.

The shorter the wavelength the more energy it has and the greater potential it has to damage living tissues. Wavelengths shorter than 0.28 micrometers (UV-C, X-rays, and gamma rays) are completely blocked by the oxygen atoms that make up 21 percent of our air. We know that wavelengths longer than 0.4 micrometers are not damaging to our eyes because we are bombarded continuously for 100 years or more without ill-effects. It is the wavelengths between 0.28 and 0.32 micrometers that may have the potential to harm us. These are the wavelengths that used to be stopped almost completely by the 320 Dobson units of ozone molecules in the undamaged ozone layer. However, as the ozone layer thins, more UV-B and UV-A pass through the atmosphere. The percent of UV-B radiation that passes through the atmosphere increases by about 1.6 percent for each ten-unit drop in Dobson units.5 Not enough ozone molecules remain between 10 miles and 22 miles up to protect us effectively.

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