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Science and Society

Acid Rain
cid rain is a general term used to de- BOX TABLE 20.1 emissions that result in a precipitation pH
Ascribe any acidic substances, wet or of 4.0 to 4.5. Unfortunately, the area of New
dry, that fall from the atmosphere. Wet The approximate pH of some England and adjacent Canada downwind
acidic deposition could be in the form of common acidic substances of major acid rain sources has granite bed-
rain, but snow, sleet, and fog could also be rock, which means that the effects of acid
Substance pH (or pH Range)
involved. Dry acidic deposition could in- rain will not be moderated as they would in
clude gases, dust, or any solid particles that the West or Midwest. This region is the geo-
Hydrochloric acid (4%) 0
settle out of the atmosphere to produce an graphic center of the acid rain problem in
Gastric (stomach)
acid condition. North America. A solution to the problem
solution 1.6–1.8
Pure, unpolluted rain is naturally is being sought by (1) using fuels other than
Lemon juice 2.2–2.4
acidic. Carbon dioxide in the atmosphere fossil fuels when possible and (2) reducing
Vinegar 2.4–3.4
is absorbed by rainfall, forming carbonic the thousands of tons of sulfur and nitrogen
Carbonated soft drinks 2.0–4.0
acid (H 2 CO 3 ). Carbonic acid lowers the pH oxides that are dumped into the atmosphere
of pure rainfall to a range of 5.6 to 6.2. De- Grapefruit 3.0–3.2 each day when fossil fuels are used.
caying vegetation in local areas can provide Oranges 3.2–3.6
more CO 2 , making the pH even lower. A pH Acid rain 4.0–5.5
range of 4.5 to 5.0, for example, has been Tomatoes 4.2–4.4
QUESTIONS TO DISCUSS
measured in rainfall of the Amazon jungle. Potatoes 5.7–5.8
Human-produced exhaust emissions of sul- Natural rainwater 5.6–6.2 Discuss with your group the following
fur and nitrogen oxides can lower the pH Milk 6.3–6.7 questions concerning acid rain:
of rainfall even more, to a range of 4.0 to
Pure water 7.0 1. Should fossil fuel use be taxed to cut
5.5. This is the pH range of acid rain (Box
the source of acid rain and fund solu-
Table 20.1).
tions? Give reasons with your answer.
The sulfur and nitrogen oxides that pro-
duce acid rain come from exhaust emissions Chemical weathering by acid rain also can 2. Electric utilities are required to
of industries and electric utilities that burn cause deterioration of buildings and other remove sulfur dioxide from power
fossil fuels and of cars, trucks, and buses. The structures. plant exhaust according to the best
oxides are the raw materials of acid rain and The type of rocks making up the local technology that was available when
are not themselves acidic. They react with landscape can either moderate or aggravate the plant was constructed. Should
other atmospheric chemicals to form sulfates the problems of acid rain. Limestone and they retrofit all plants with more
and nitrates, which combine with water vapor the soils of arid climates tend to neutralize expensive technology to reduce the
to form sulfuric acid and nitric acid. These acid, while waters in granite rocks and soils amount released even more? What if
are the chemicals of concern in acid rain. cannot neutralize acid and tend already to doing so would increase your electric
Acid rain falls on the land, bodies of be somewhat acidic. bill by 50 percent? Would you still
water, forests, crops, buildings, and people, Although natural phenomena, such as support further reductions in the
so the concerns about acid rain center on volcanoes, contribute acids to the atmo- amount of sulfur dioxide released?
its environmental impact on lakes, for- sphere, human-produced emissions of sul- 3. What are the advantages and dis -
est, crops, materials, and human health. fur and nitrogen oxides from burning advantages of a total ban on the use
Acid rain accelerates chemical weathering, fossil fuels are the primary cause of acid of fossil fuels?
leaches essential nutrients from the soil, and rain. The heavily industrialized part of the 4. Brainstorm with your group to see
acidifies lakes and streams. All of these pro- United States, from the Midwest through how many solutions you can think of
cesses affect plants, animals, and microbes. New England, releases sulfur and nitrogen to stop acid rain damage.

Deflation, after the Latin meaning “to blow away,” is the longed drought, dust storms, and general economic disaster for
widespread picking up of loose materials from the surface. farmers in the area is known as the Dust Bowl episode.
Deflation is naturally most active where winds are unobstructed The most common wind-blown deposits are (1) dunes and
and the materials are exposed and not protected by vegetation. (2) loess. A dune is a low mound or ridge of sand or other sedi-
These conditions are often found on deserts, beaches, and un- ments. Dunes form when sediment-bearing wind encounters an
planted farmland between crops. During the 1930s, many farm- obstacle that reduces the wind velocity. With a slower velocity,
ers in the Plains states replaced the native grassland vegetation the wind cannot carry as large a load, so sediments are deposited
when they established farms. A series of drought years occurred on the surface. This creates a larger windbreak, which results in a
and the crops died, leaving the soil exposed. Unusually strong growing obstacle, a dune. Once formed, a dune tends to migrate,
winds eroded the unprotected surface, removing and transport- particularly if the winds blow predominantly from one direction.
ing hundreds of millions of tons of soil. This period of pro- Dunes are commonly found in semiarid areas or near beaches.

20-13 CHAPTER 20 Shaping Earth’s Surface 513