The Harmful Effects of Acid Rain

Buildings and statues constructed of marble are sensitive to the destructive action of acid rain. How can the same reactions that destroy marble be used to help reduce the harmful effects of acid rain pollution ... 

In some cases the effects of acid rain can be partly offset by the hardness of water. One can take as an example the harmful effect of acid rain on mollusks tests, less evident in lakes containing harder water. 

Identical net ionic reactions with sulfuric and nitric acids protect lakes bounded by limestone deposits from the harmful effects of acid rain. 

One of the harmful effects of acid rain is its reaction with structures made of limestone, which include marble structures, ancient ruins, and many famous statues (Fig. 8.19). Write the equation you would expect for the reaction between acid rain, which contains sulfuric acid, and limestone, solid calcium carbonate. Write a second equation with the same reactants, showing that the expected but unstable carbonic acid decomposes to carbon dioxide and water. 

One harmful effect of acid rain is the deterioration of structures and statues made of marble or limestone, both of which are essentially calcium carbonate. The reaction of calcium carbonate with sulfuric acid yields carbon dioxide, water, and calcium sulfate. Because calcium sulfate is marginally soluble in water, part of the object is washed away by the rain. Write a balanced chemical equation for the reaction of sulfuric acid with calcium carbonate. 

These acid rains caused the water of the lakes in Scotland to have pHs of 2.4 in the 1970s, that is an acidity similar to that of vinegar. A fifth of the Swedish lakes have lost a large portion of their fish, in particular trout which cannot survive in pHs lower than 5. The agricultural damage, the corrosion of the metals of buildings, the harmful effects on the respiratory systems must also be attributed to sulphur pollution. Thus the annual cost of the corrosion by acid rains in the USA has been estimated to be worth lO l US dollars. 

In turn, SO3 can react with water vapor in the atmosphere to produce H2SO4 mist, a component of acid rain. Also, the reaction of H2SO4 with airborne NH3 produces particles of (NH4)2S04- The details of the effect of low concentrations of SO2 and H2SO4 on the body are not well understood, but it is clear that these substances are respiratory irritants. Levels above 0.10 ppm are considered potentially harmful. 

The waste streams created by utility systems tend, on the whole, to be less environmentally harmful than process waste. Unfortunately, complacency would be misplaced. Even though utility waste tends to be less harmful than process waste, the quantities of utility waste tend to be larger than process waste. This sheer volume can then result in greater environmental impact than process waste. Gaseous combustion products contribute in various ways to the greenhouse effect, acid rain and can produce a direct health hazard because of the formation of smog. The aqueous waste generated by utility systems can also be a major problem if it is contaminated. 

Small amounts of some contaminants can be serious. When we burn coal, not only do we produce carbon dioxide, the major product, but we can liberate small amounts of mercury and larger amounts of sulfur dioxide. The mercury can form toxins that harm fish as well as humans, while sulfur dioxide can produce acid rain that destroys forests and water supplies. How can these contaminants be most effectively removed or dealt with And how can we generate the energy that we need without releasing such by-products ... 

Beneficial and Harmful Effects. At low levels, sulfur dioxide in the atmosphere is not harmful to crops, but damage can occur at excessive levels (305—309). Crops differ gready in their sensitivity. Forest damage attributed to acid rain is often cited but the observed symptoms seem to have multiple causes and the contribution of sulfur acids is unspecified. The sulfur in precipitation is, up to a point, beneficial to plant growth because sulfur is an essential nutrient. Lessening the sulfur content of the atmosphere requires that supplementary sulfur be provided in fertilizer to some crops some crops already require supplementary sulfur. Sulfur dioxide itself has been found useful in drip irrigation systems (310,311) and in calcareous soils (308). Small field generators have been developed for this purpose. 

Unpolluted rain is not harmful. However, many industrial and power plants burn coal and oU. The smoke produced may contain large quantities of sulfur oxides, suspended particles, and nitrogen oxides. Automobiles also contribute to the problem by emitting similar oxides. These chemicals react with water in the air to form acids, such as sulfuric acid. These acids reach the surface of Earth in fog, rain, snow, and dew. Acid rain can have a disastrous effect when it reaches bodies of water and waterways. But if a lake has a high limestone content, it is able to somewhat neutralize the acid. 

Acid rain is not a new phenomenon either in Asia or in other parts of the world. Acid rain was first reported in Europe in the 19th century (Ducros, 1854). Acid rain and its harmful effects have been extensively studied in the industrialized countries of Europe and North America over the last thirty years (Radojevic and Harrison, 1992). 

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