Page 493 - Environment: The Science Behind the Stories

to buffer themselves against acid deposition. This also means
that once calcium or similar ions are leached from a soil, the
soil becomes more sensitive to acidification.
Besides altering natural ecosystems, acid precipitation
damages crops, erodes stone buildings, corrodes cars, and
erases the writing from tombstones. Ancient cathedrals in
Europe, monuments in Washington, D.C., temples in Asia,
and stone statues in London are experiencing billions of dol-
lars of damage as their features dissolve away (Figure 17.30).
Because the pollutants leading to acid deposition can
travel long distances, their effects may be felt far from their
sources. For instance, much of the pollution from power
plants and factories in Pennsylvania, Ohio, and Illinois falls
out in states to their east, including New York, Vermont, and
New Hampshire, as well as in regions of Canada to the north.
As a result, regions of greatest acidification tend to be down-
wind from heavily industrialized source areas of pollution.

We are addressing acid deposition
Figure 17.29 Acid deposition killed these trees on Mount
Mitchell in North Carolina. The emissions trading program for sulfur dioxide established
by the Clean Air Act of 1990 has helped us address acid depo-
over 1000 times more acidic than normal rainwater) has envel- sition. The economic incentives created by this cap-and-trade
oped forests for extended periods, killing trees (Figure 17.29). program have encouraged polluters to invest in technologies
When acidic water runs off from land, it affects streams, such as scrubbers (p. 479) and to devise other ways to become
rivers, and lakes. Thousands of lakes in Canada, Scandinavia, cleaner and more efficient. As a result, SO emissions across
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the United States, and elsewhere have lost their fish because the United States have fallen by 67%, and the program is now
acid precipitation leaches aluminum ions out of soil and rock preventing the emission of 10 million tons of SO per year
2
and into waterways, where they damage the gills of fish and (see Figure 7.16, p. 201). The EPA has calculated that the pro-
disrupt their salt balance, water balance, breathing, and cir- gram’s economic benefits outweigh its costs by 40 to 1.
culation. Terrestrial animals are affected, too; populations As a result of declining SO emissions, average sulfate
2
of snails and other invertebrates typically decline, and this loads in precipitation across the eastern United States were
reduces the food supply for birds. 51% lower in 2008–2010 than in 1989–1991. Emissions
The severity of all these effects depends not only on the of NO also have been lowered significantly, thanks to the
X
pH of the deposition, but also on the acid-neutralizing capacity emissions-trading program, and wet nitrogen deposition
of the soil, rock, or water that receives the acidic input. Sub- declined between these periods as well. As a result, air and
strates differ naturally in their chemistry and pH, and regions water quality has improved throughout the eastern United
with more alkaline soil, rock, or water have a greater capacity States (Figure 17.31).

(a) Before acid rain damage (b) After acid rain damage

Figure 17.30 Acid deposition corrodes statues and buildings. Shown is an Egyptian obelisk known as
492 Cleopatra’s Needle, in Central Park, New York City, (a) before and (b) after the onset of significant acid deposition.

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