Environmental Engineering Reference
In-Depth Information
TABLE 3.1
Names of Various Ranges of Wavelengths of Light and Their Biological Relevance
Name
Wavelength (m)
Biological relevance
10
4
-1
10
4
Radio
2
Little effect
10
4
-10
6
Infrared
Heats water, some bacteria can use near
infrared for photosynthesis
10
7
-5.7
10
7
Visible red-orange
7
(700-570 nm)
Visible, photosynthetically active, heats water
10
7
-4.9
10
7
Visible green
5.7
(570-490 nm)
Visible, photosynthetically active (some algae),
heats water
10
7
-4.0
10
7
Visible blue
4.9
(490-400 nm)
Visible, photosynthetically active, heats water
10
7
-3.2
10
7
Ultraviolet UVA
4.0
(400-320 nm)
Mutagenic, cell damage
10
7
-2.8
10
7
Ultraviolet UVB
3.2
(320-280 nm)
Mutagenic, cell damage
10
7
-2.0
10
7
Ultraviolet UVC
2.8
(280-200 nm)
Mutagenic, cell damage, not present at
significant levels in natural environments
10
8
-10
13
Extreme UV, X-rays,
Mutagenic, cell damage, not present at
gamma rays
significant levels in natural environments
The earth's atmosphere alters the intensity and composition of solar ir-
radiance that reaches aquatic systems. Some atmospheric components re-
move specific wavelengths of light (Fig. 3.4). Others, such as dust and
clouds, may scatter or absorb light less selectively. One of the most impor-
tant aspects of atmospheric influence on irradiance is the absorption of ul-
traviolet (UV) light by atmospheric ozone. Releases of chlorofluorocarbons
2.5
Outside atmosphere
At sea level
2.0
1.5
1.0
0.5
UV
Visible
Infrared
0.0
0.1
0.4
0.7
1.0
1.4
1.7
2.0
Wavelength (
μ
m)
FIGURE 3.4
Spectral energy distribution of solar radiation outside the earth's atmosphere
and inside the atmosphere at sea level. Note how the atmosphere changes the spectral distri-
bution of light (after U.S. Air Force, 1960).
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