Global Stratospheric Ozone Reduction - Air Pollution and Global Warming: History, Science, and Solutions - page 258

locations, such as northern Europe, CM is as common
as is SCC.
Susceptibility to skin cancer depends on a combina-
tion of skin pigmentation and exposure. For people with
sensitive skin, it is not necessary to be exposed to UV-B
overalifetime for a person to develop skin cancer. Skin
cancer rates usually increase from high latitudes (from
the poles) to lower latitudes (to the Equator).

and pigment contents (Hader et al., 1998). Because
these microorganisms are near the bottom of the food
chain, their deaths affect higher organisms. Algae and
sea grasses, which cannot avoid exposure to the sun, are
also susceptible to UV-B damage.
Animals are susceptible to several of the same UV-B
hazards as humans. SCCs have been found in cats, dogs,
sheep, goats, horses, and cattle, usually on unprotected
skin, such as eyelids, noses, ears, and tails (Hargis,
1981; Teifke and Lohr, 1996; Mendez et al., 1997).
Cataracts and skin lesions have been found in fish
(Mayer, 1992).
UV damage to crops varies with species and the
crop's ability to adapt. UV-B affects the DNA in some
crops and the rate of photosynthesis in others. For many
crops, UV-B changes lifecycle timing, plant form, and
production of plant chemicals (Caldwell et al., 1998).
For others, it makes them more susceptible to dis-
ease and attack by insects. Crop yields of some plants
are affected by enhanced UV-B, but those of others
are not.

11.9.1.2. Effects on Eyes
The cornea ,which covers the iris and the lens, is the tis-
sue most susceptible to UV-B damage to the eye. Little
UV-B radiation penetrates past the lens to the vitreous
humor or the retina, the tissues behind the lens. The most
common eye problem associated with UV-B exposure
is photokeratitis or snow blindness ,aninflammation
or reddening of the eyeball. Other symptoms include a
feeling of severe pain, tearing, avoidance of light, and
twitching (Longstreth et al., 1998). These symptoms are
prevalent not only among skiers, but also among people
who spend time at the beach or other outdoor locations
with highly reflective surfaces.
From a public cost perspective, the most expensive
eye-related disease associated with UV-B radiation is
cataract ,adegenerative loss in the transparency, thus
cloudiness, of the lens (Figure 11.19b) that frequently
leads to blindness unless the damaged lens is removed.
Worldwide, cataract is the leading cause of blindness.
More severe, but less widespread, eye-related dis-
eases are squamous-cell carcinoma, which affects the
cornea, and ocular melanoma ,which affects the iris
and related tissues.

11.9.3. Effects on the Global Carbon
and Nitrogen Cycles
Changes in UV-B radiation affect the global carbon and
nitrogen cycles. UV-B damages phytoplankton, reduc-
ing their consumption of CO 2 (g) by photosynthesis.
UV-B also enhances photodegradation (breakdown by
light) of dead plant material, causing the release of more
CO 2 (g) back to the air. UV-B enhances the release of
carbon monoxide gas [CO(g)] from charred vegetation
(Zepp et al., 1998). It also affects the rate of nitrogen
fixation by cyanobacteria (Hader et al., 1998).

11.9.1.3. Effects on the Immune System
Human skin contains numerous cells to fight infection
that are produced by the immune system. Enhanced
UV-B radiation has been linked to suppression of these
cells, reducing resistance to certain tumors and infec-
tions. Suppressed immune responses to UV-B have been
reported for herpes, tuberculosis, leprosy, trichinella,
candidiasis, leishmaniasis, listeriosis, and Lyme disease
(Longstreth et al., 1998).

11.9.4. Effects on Tropospheric Ozone
Increases in UV-B radiation increase photolysis rates
of gases such as ozone, nitrogen dioxide, formalde-
hyde, hydrogen peroxide, acetaldehyde, and acetone.
Increases in photolysis rates of nitrogen dioxide,
formaldehyde, and acetaldehyde increase rates of free-
tropospheric ozone formation (Tang et al., 1998).
Whereas reductions in stratospheric ozone increase
UV-B penetration to the background troposphere,
increases in aerosol concentrations in urban air can
either decrease or increase UV-B penetration to the sur-
face. Absorption of UV-B by aerosol particles reduces
UV-B penetration within and below the particles,
depressing ozone formation in polluted air (Section
7.1.3.3). Scattering by aerosol particles increase UV-
B, causing the opposite effect.

11.9.2. Effects on Microorganisms,
Animals, and Plants
Increases in UV-B radiation affect microorganisms, ani-
mals, and plants in a variety of ways. Phytoplankton,
which live on the surfaces of the oceans, are suscep-
tible to slowed growth, reproductive problems, and
changes in photosynthetic energy-harvesting enzymes