Effects of Pollution on Visibility, Ultraviolet Radiation, and Colors in the Sky - Air Pollution and Global Warming: History, Science, and Solutions - page 154

Table 7.1. Wavelengths of absorption in the visible
and ultraviolet spectra by atmospheric gases

Chemical Absorption

Gas name formula wavelengths ( m)

Visible/Near-UV/Far-UV Absorbers
Ozone O 3 (g) < 0.35, 0.45-0.75

<

Nitrate radical NO 3 (g) 0.67

<

Nitrogen dioxide NO 2 (g) 0.71

Near-UV/Far-UV Absorbers
Formaldehyde

HCHO(g) < 0.36

Nitric acid HNO 3 (g) < 0.33

Far-UV Absorbers
Molecular oxygen O 2 (g) < 0.245

Carbon dioxide CO 2 (g) < 0.21

Water H 2 O(g) < 0.21

Molecular nitrogen N 2 (g) < 0.1

UV, ultraviolet.

gases that absorb visible or UV radiation. Of the gases,
all absorb UV, but only a few absorb visible radiation.
Gases that absorb visible or UV radiation are often, but
not always, photolyzed by this radiation into simpler
products.
The gases that affect UV radiation the most are
molecular oxygen [O 2 (g)], molecular nitrogen
[N 2 (g)], and ozone [O 3 (g)]. Oxygen absorbs wave-
lengths shorter than 0.245

Figure 7.1. Sir Isaac Newton (1642-1727). Edgar Fahs
Smith Collection, University of Pennsylvania Library.

is divided into wavelengths of Newton's primary col-
ors, blue (0.38-0.5 m), green (0.5-0.6 m), and red

(0.6-0.75 m).

When radiation passes through the Earth's atmo-
sphere, it is attenuated or redirected by absorption and
scattering by gases, aerosol particles, and hydrometeor
particles. These processes are discussed next.

m, and nitrogen absorbs

wavelengths shorter than 0.1 m. Oxygen and nitrogen

prevent nearly all solar wavelengths shorter than 0.245

m from reaching the troposphere.
In 1880, M. J. Chappuis found that ozone also
absorbed visible radiation between the wavelengths of
0.45

7.1.1. Gas Absorption
Absorption occurs when radiative energy (e.g., from
the sun or Earth) enters a substance and is converted
to internal energy, changing the temperature of the
substance. The substance then reradiates some of the
internal energy back to the air at a longer (thermal-IR)
wavelength, heating the air. Absorption removes radi-
ation from an incident beam, reducing the amount of
radiation received past the point of absorption. Next,
absorption by gases is discussed with respect to the
solar spectrum.

m. The absorption bands in this
wavelength region are now called Chappuis bands .
In 1881, Walter N. Hartley first suggested that ozone
waspresent in the upper atmosphere and hypothesized
that the reason that the Earth's surface received lit-
tle radiation shorter than 0.31

m and 0.75

mwas because ozone
also absorbs these wavelengths. The absorption bands
of ozone below 0.31

marenowcalled the Hart-
ley bands .In1916, English physicists Alfred Fowler
(1868-1940) and Robert John Strutt (1875-1947; the
son of Lord Baron Rayleigh) showed that ozone also
weakly absorbs wavelengths between 0.31

7.1.1.1. Gas Absorption at Ultraviolet and
Visible Wavelengths
Gases selectively absorb radiation in different portions
of the electromagnetic spectrum. Table 7.1 lists some

m and

0.35 m. The bands of absorption in this region are

now called the Huggins bands .Ozone absorption of
UV and solar radiation, followed by reemission of