Acid rainfall

The term acid rain was first used in 1872 by Robert Angus Smith, an English chemist and climatologist. He used the term to describe the acidic precipitation that fell on Manchester, England, at the start of the Industrial Revolution. Although neutral water has a pH of 7, rainwater becomes naturally acidified from dissolved carbon dioxide, a normal component of the atmosphere. The carbon dioxide, whose solubihty in water at room temperature is 3.4 g/L reacts reversibly with water to form a solution of the weak acid carbonic acid. 

At equilibrium, the pH of rainfall saturated with CO2 from the air is 5.6. Any precipitation with a pH below 5.6 is considered to be acid rain. 

As you have seen, NO2, SO2, and SO3 can both react with water in the atmosphere to produce acids NO2 produces nitric acid (HNO3) and nitrous acid (HNO2) SO3 and SO2 produce sulfuric acid (H2SO ) and sulfurous acid (H2SO3). When conditions are favorable, water droplets carrying these acids precipitate as rain or snow with a low pH. Ice core samples taken in Greenland and dating back to 1900 contain sulfate (SO ) and nitrate (NO ) ions. This indicates that at least from 1900 onward, acid rain has been commonplace. 

The extent of the problems with acid rain can be seen in dead (fishless) ponds and lakes, dying or dead forests, and crumbling buildings. For the most part, dead lakes are still picturesque, but no fish can live in the acidified water. Lake trout and yellow perch die at pH values below 5.0, and smaU-mouth bass die at pH values below 6.0. Mussels die when the pH is below 6.5. 

FIGURE 11.2 Air pollution can cause acid rain to fall far from where the pollutants are generated. 

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Huchinson T.C., Whilby L.M. The effects of acid rainfall and heavy metals particulates on a boreal forest ecosystem near the Sudbury smelting region of Canada. Water Air Soil Pollut 1977 7 421 438. 

Coke does not offer the same potential environmental issues as other petroleum products (Chapter 10 and above). It is used predominantly as a refinery fuel unless other uses for the production of a high-grade coke or carbon are desired. In the former case, the constituents of the coke that will release environmentally harmful gases such as nitrogen oxides, sulfur oxides, and particulate matter should be known. In addition, stockpiling coke on a site where it awaits use or transportation can lead to leachates as a result of rainfall (or acid rainfall) which are highly detrimental. In such a case, application of the toxicity characteristic leaching procedure... 

Figure 6-7 pH of various substances. [From Chem. Eng. News. 14 September 1981.] The most acidic rainfall (Box 15-1) is a stronger acid than lemon juice. The most acidic natural waters known are mine waters, with total dissolved metal concentrations of 200 g/L and sulfate concentrations of 760 g/L The pH of this water, -3.6, does not mean that [H ] = 103- M ... 

Between 1980 and 1990, j mm of the thickness of the external stone walls of St. Paul s Cathedral in London was dissolved by acidic rainfall. A comer of the building facing a power station dissolved at 10 times the rate of the rest of the building until the station was closed. The power station and other industries that burn coal emit S02, which is a majoi source of acid rain (described in Box 15-1). Loss of heavy industry and laws limiting emissions decreased atmospheric S02 from as high as 100 ppb in the 1970s to 10 ppb in 2000. Correspondingly, only mm of St. Paul s external stone disappeared between 1990 and 2000. 2... 

Synthetic acid rain samples have been allowed to percolate through pieces of coquina, the material of construction at Castillo de San Marcos National Monument, St. Augustine, Florida. Chemical analyses of the solutions are used to determine the extent of dissolution of the coqiuna, a limestone material, by acid rain. Because of the location of the Castillo on the Atlantic coast, the effect of salt spray on weathering of coquina appears to be as significant as the influence of acid rainfall. 

To illustrate the effect of ionic strength on degradation of calcium carbonate we have calculated the solubility of calcium carbonate in deionized water, acid at pH = 4.0 and acid rain at pH = 4.0 with an ionic strength of 7.2 x 10 in the absence of CO2. The results of these calculations are shown in Table 2 and are plotted in Figure 3. These data show that the ionic strength contribution of sea spray and other atmospheric sources are as significant as the neutralization reaction with acid at pH = 4.0 in the degradation of coquina by acid rainfall. 

Biological acid production (bicarbonate leaching) Excess base uptake by roots =1.1 Acid rainfall (rainwater pH = 4.3-4.4) = 0.67 KCl-exchangeable acidity = 100-275 Total titratable acidity = 500-800... 

The pH of the acid rainfall is raised by contact with the hardwood canopy, but not by contact with the conifers. 

One of the most acidic rainfalls ever recorded occurred in West Virginia. The pH of the rain was about 3. Approximately how much more concentrated is the hydronium ion in this acid rain than that in rain with a pH of 5 ... 

Most of the limestone used in agriculture is applied directly to the soil. Smaller amounts are used as a filler and conditioner in fertiliser formulations. It is also used in animal feeds, and as poultry grit. Furthermore, limestone is increasingly being employed to combat the adverse effects of acid rainfall. 

Liming of lakes or streams is the only large scale measure available to counter some of the adverse effects of acid rainfall. It will need to be continued until the emission of acid gases is substantially reduced. 

Leaves of pin oak showed a different sequence of steps in leaf injury from that seen in other plant species. Initially, injury began with collapse of adaxial epidermal cells. Initial lesions consisted of approximately one to six collapsed epidermal cells which resulted in a slight depression on the leaf surface. At this stage, all cells in the mesophyll layers, and the abaxial epidermis were unaffected. After several more simulated acid rainfalls larger lesions, with increased surface area and depth, developed from smaller lesions. These lesions encompassed five to fifteen collapsed epidermal cells. Penetration of acidic solutions into the mesophyll tissues resulted in collapse of epidermal and underlying palisade parenchyma cells. 

Acid rainfall treatments above the pH of 4.0 have not usually shown significant effects on soils in the limited time frame of experiments conducted thus far. 

You will also see that some pollutants (sulfur oxides and nitrogen oxides) have a major impact on our environment as primary contributors to acid rainfall. You will need some knowledge of water chemistry and of the pH scale to fully appreciate this problem, so we will defer that discussion until Chapter 11. 

Water dissolves all kinds of substances and reacts chemically with many of the atmospheric pollutants we ve encountered in earlier chapters. Several nitrogen oxides and sulfur oxides react readily with water in the atmosphere to produce acidic rainfall that can have a very negative impact on our environment and on many building materials. Dissolved substances in liquid water can include natural minerals and chemicals, manmade fertilizers and pesticides, gasoline and fuel additives, toxic chemicals of all types, and even unused antibiotics that people have flushed down the toilet. To minimize environmental damage and to ensure a safe and adequate water supply, we must limit all types of pollution. We must control both the amount of pollution and the types of pollution to which we subject our water supply because what we ve got is all there is. The water must be used, reused, and used s ain, over and over, in a never-ending cycle. If it becomes polluted, we will have to clean it up. 

What is acid rainfall, and what are some of its effects ... 

How does acid rainfall differ from other forms of water pollution ... 

Acid rain dams es trees in several ways. It disturbs the stomata (openings) in tree leaves and causes increased transpiration and a water deficit in the tree. The surface structures of the bark and the leaves can also be destroyed by the acid. Acid rainfall can acidify the soil, damaging fine root hairs and thus diminishing nutrient and water uptake. In addition, acid rain dissolves minerals that are insoluble in groundwater and surface waters of normal pH, and many of these minerals contain metal ions toxic to plant life. For example, acid rain dissolves aluminum hydroxide in the soil, allowing aluminum ions (Al ) to be taken up by the roots of plants, where they have toxic effects. 

Acid rainfall is rainfall that is more acidic than pH 5.6. Nitrogen oxides and sulfur oxides emitted by combustion processes produce nitric acid and sulfuric and sulfurous acids, which are the main contributors to acid rainfall. 

Chapter 11 is a new chapter including material from Chapters 5, 15, and 16 of the previous edition. The focus is on water, its unique properties and its importance for life, acid rainfall and water pollution, and water purification. There is a significantly expanded discussion illustrating the uniqueness of water by comparing it with several compounds of comparable size and molecular weight. The issue of water shortage problems worldwide is discussed. 

Limestone is made from CaC03. Acid rainfall (e.g., containing HCl) initiates the formation of a water-soluble CaCl2 salt and carbonic acid, which falls apart giving H2O and CO2 ... 

Figure 8-2 pH values of various substances. The most acidic rainfall in the United States is more acidic than lemon juice. 

Most acidic rainfall recorded in U.S. at Wheeling, WV - Battery acid... 

Determine your location on the map in Figure 14.20. What is the pH of rain where you live What is the [H3O+] 90. Identify the area of the United States with the most acidic rainfall on the map in Figure 14.20. What is the pH of the rain What is the [H30 ] ... 

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