THE EFFECTS OF ACID RAIN

To date, the major adverse effects of acid rain include damage to lakes, streams, and forests degradation of soils leaching of toxic metals in the environment damage to man-made materials adverse respiratory effects in humans and degradation of air quality. It is very difficult to predict the future effects of acid rain on something as complex as an entire ecosystem. We do not know whether most of the effects that will occur have already taken place, or whether we have only seen the tip of the acid iceberg to come. 

During the past several decades, acid rain in eastern North America has caused sensitive lakes and streams to acidify, leading to the decline and death of fish and other aquatic life. The ex- 

To appreciate the pressure that acid rain has put on sensitive lakes and streams, compare the acidity of rain with the acidity of lake water. Healthy lakes normally have a pH around 5.6 and above. When a lake becomes as acidic as pH 5.0, adverse biological effects set in. At pH 4.5 or below, a lake is usually considered dead — incapable of supporting the rich variety of life found in healthy lakes. Yet precipitation in the eastern U.S. is several times more acidic still (average pH 4.3), and in the northeastern U.S. it is as acidic as pH 4.0. Thus if lakes and streams were simply huge puddles of rainwater, every lake east of the Mississippi River would be virtually devoid of life. What prevents this catastrophe is that acid rain is largely neutralized by the soils and rocks underlying most watersheds. The most common alkaline rocks are limestone and dolomite (calcium and magnesium carbonates), which are chemically similar to com-merical stomach antacids. 

However, large areas in the United States contain rocks that are poor buffers (such as granites, gneisses, and quartzites) and that give rise to poorly buffering soils. These areas include the northeastern U.S. parts of the Appalachians, Smoky Mountains and southern states the Boundary Waters Canoe Area in Minnesota, and parts of northern Wisconsin and parts of the Pacific Northwest and the Rocky Mountains. 

An alkalinity of 200 microequivalents per liter is arbitrarily taken as a cutoff for sensitivity to acid ram i If a body of water with this alkalinity is mixed with a roughly equal volume of acid 

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The effects of acid rain are particularly severe in areas where the bedrock is granite or other materials incapable of neutralizing H+ ions. As the concentration of acid builds up in a lake, aquatic life, from algae to brook trout, dies. The end product is a crystal-clear, totally sterile lake. 

The human impact on the environment affects many areas of our lives and future. One example is the effect of acid rain on biodiversity, the diversity of living things. In the prairies that extend across the heartlands of North America and Asia, native plants have evolved that can survive even nitrogen-poor soil and drought. By studying prairie plants, scientists hope to breed food plants that will be hardy sources of food in times of drought. However, acid rain is making some of these plants extinct. 

Explain how titration might be used to deter- 2. Explain how titration might be used for mine the effects of acid rain on the medical testing,... 

A trout fishery added limestone to their loch to combat the effects of acid rain. They managed to increase the pH of the water from 4 to 6. The concentration of H (aq)... 

A method sometimes used to counteract the effects of acid rain is the addition of a basic substance that wiii neutraiize the water s acidity, iime in the example shown here, to a body of water. (Martin Bond/Photo Researchers, inc.)... 

Higher pH of meltwater may act to lessen the effects of acid rain and snow. 

York and New England are devoid of fish due to the effects of acid rain. Indirect effects of the low pH values associated with acid rain also affect organisms. As noted in Table 13.1, one of the properties of an acid is the ability to dissolve certain metals. This has a profound effect on soil subjected to acid rain. Acid rain can mobilize metal ions such as aluminum, iron, and manganese in the basin surrounding a lake. This not only depletes the soil of these cations disrupting nutrient uptake in plants, but also introduces toxic metals into the aquatic system. 

The effects of acid rain can be seen in lakes and streams, in forests, and on all kinds of structures. The lowered pH kills fish eggs, fish, and many other organisms that live in lakes and streams. In forests, the acid can kill the leaves and needles of trees. It damages the soil by depleting it of nutrients, which stunts plant growth. Acid rain also eats away at the surfaces of buildings and other structures. Structures made of marble and other calcium-containing stone are particularly sensitive to acid rain. 

The two photographs in (a) show the same obelisk before and after the effects of acid rain, (b) Many forests downwind from heavily industrialized areas, such as in the northeastern United States and in Europe, have been noticeably hard-hit by acid rain. 

Money has been made available to solve the problem of acid rain. Attempts are being made to clean gases being released from power stations and to look into ways in which the effects of acid rain can be reversed. The table below and Figure 12.5 (p. 199) give some data about the emission of sulfur dioxide. 

In recent years, the effects of acid rain on lake water, heavy metals contaminated soils and structural materials have been widely discussed (1). Sulfur and nitrogen contained in fossil fuels are released into the atmosphere by combustion. Sulfur and nitrogen oxides dissolve in rain drops as bisulfite, sulfite and nitrite ions. These components are further oxidized into sulfate and nitrate ions. Since these species lower pH, it is important to accurately determine them in rain water. However, these ions are difficult to analyze because they rapidly oxidize in the presence of catalysts such as ferric and manganous ions. Light, temperature, and pH also affect the oxidation rate of S(IV). 

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. 

Mineral dissolution kinetics influence such phenomena as development of soil fertility, amelioration of the effects of acid rain, formation of karst, acid mine drainage, transport and sequestration of contaminants, sequestration of carbon dioxide at depth in the earth, ore deposition, and metamorphism. On a global basis, mineral weathering kinetics are also involved in the long-term sink for CO2 in the atmosphere ... 

The effect of acid rain on a stand of trees in the Great Smoky Mountains of the United States. 

We ve all heard about the ravages of acid rain. Resulting from toxic emissions in the environment, acid rain damages the leaves and needles on trees, reduces a tree s ability to withstand cold, drought, disease, and pests, and even inhibits or prevents plant reproduction. In an effort to stay alive and combat the acidity, tree roots pull important nutrients such as calcium and magnesium from the soil. These alkaline nutrients balance the effects of acid rain, but as they become depleted from the soil, the trees ability to survive is further strained. 

For an unusual connection with acid rain, browse to the Scientific American Web site and perform a search using the words acid rain. One of the hits should be an article on the effects of acid rain following the impact of a comet with Earth. How would the effects of such an impact compare with the effects from pollution that we have observed over the past few decades ... 

New and exciting chapter opening introductions, accompanied by applied photos, present a relevant example of one of the chapter topics. Examples include stalagmites and stalactites as an illustration of an equilibrium process (Chapter 9), the effects of acid rain (Chapter 16), and the oxidation/reduction properties of chlorophyll (Chapter 19). 

It is probably true to say that the term environmental chemistry has no precise definition. It means different things to different people. We are not about to offer a new definition. It is clear that environmental chemists are playing their part in the big environmental issues—stratospheric ozone (C) () depletion, global warming and the like. Similarly, the role of environmental chemistry in regional-scale and local problems—for example, the effects of acid rain or contamination of water resources—is well established. This brief discussion illustrates the clear link in our minds between environmental chemistry and human beings. For many people, environmental chemistry is implicitly linked to pollution . We hope this book demonstrates that such a view is limited and shows that environmental chemistry has a much wider scope. 

The effect of acid rain on mortars will depend on the particular mortar in consideration. The most susceptible mortars will be the lime-sand ones. The carbonated lime will be particularly attacked due to the small crystal size of the formed calcite (19,20). The resulting calcium sulfate can crystallize as gypsum [CaS0. 2H20] inducing mechanical stresses into the matrix of the mortar. 

There has been research that suggests that the growth of trees could be affected if acid rain has a long term acidifying effect on soils. The ultimate implication of the effects of this pollutant as it impacts tree growth will be in terras of tree productivity and wood quality. This could influence products such as paper and wood for furniture, blight our landscape and affect roofs, decks, telephone poles, and fences. Little work has been done on the effect of acid rain on wood products. However, work on wood chemistry indicates that acid rain has the potential and the characteristics needed to be a destructive force to these materials. 

The effect of acid rain on leaf litter should be viewed in conjunction with the effect of acid rain on the underlying soils. 

There was little research available in the literature on the effects of acid rain on wood products. Letters to various utility companies also indicated that there was little work done in this area. However, the available literature will be cited and integrated with current knowledge in the area of wood science. 

The research available to date presents a partial view of the impacts of acid rain on woody plants. Many of the impacts are still only potential impacts, as simulation studies versus field studies present a conflicting view. However, one thing appears quite clear - more research is needed. As many researchers have found, the effect of acid rain is not going to be one of simple cause and effect, but rather one of a multiple factor interaction. Thus, future work should be statistically designed to test the inter-action(s) rather than main effects. Work needs to be done over both the short and long term to assess injury. Basic physiological work across disciplines with the standardization of techniques used (e.g. one set type of simulator for all researchers to produce simulated acid rain) must be employed in order for different experimental results to be comparable. If we can discover how plants will react to given combinations of stresses, only then will we be able to propose an appropriate course of action. 

Nylon fibers are used extensively in outdoor textiles and as a result are subject to sunlight, varying temperatures and acid precipitation. The degradation of nylon by light, heat, humidity and air polluted with sulfur dioxide has been widely studied (8-13). However, little data is available on the effect of aqueous acid on nylon in the presence of heat, light and moisture (i.e. acid rain conditions). Therefore, the purpose of this work was to determine the effect of acid rain conditions on nylon. The synergistic effects of aqueous acid, light and heat on nylon were also examined. 

It is the intent of this paper to review some of the methodology and results of the NBS-BCL studies, and their relevance to the economic effects of acid rain. Since the effect of acid rain on materials would appear to be a form of corrosion (although affecting all materials, not only metals), the NBS corrosion study (1,2) will be the principal one discussed. 

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