1. Acid Deposition Lake Barkevatn in Norway used to have healthy stocks of trout and perch. As a result of acid rain, the trout stock died out in the mid-1970s and the perch stock at the beginning of the 1980s.

4. Unpolluted rain is itself slightly acidic with a pH level of about 5.6. Results from the dissolution of CO 2 (an acidic oxide) in water droplets CO 2 (g) + H 2 O(l) H 2 CO 3 (aq) H 2 CO 3 (aq) H + (aq) + HCO 3 - (aq) CO 2 (g) + H 2 O(l) H + (aq) + HCO 3 - (aq)

5. Acid Deposition The deposition of acids from the atmosphere in precipitation that falls as rain, sleet, snow, and particulates. Fog & dew can also be acidic. Mainly results from nitrogen oxides and sulfur oxides.

10. These graphs compare nitrate concentrations & pH levels in the Eastern US with less populated areas that have fewer coal-burning power plants.

11. Coal contains sulfur in the form of the mineral pyrite FeS 2 4 FeS 2 + 11 O 2 2 Fe 2 O 3 + 8 SO 2 A 1000 megawatt coal-fired electricity generating plant burns ~700 tons of coal per hr @4% S 56 tons SO 2 generated per hour 490,560 tons SO 2 per year

14. Other Sources of Sulfur Volcanoes Microbes & plants Smelters

15. Nonferrous smelting facilities are large point sources (individual sites emitting large amounts of a pollutant) of SO 2 Many useful metals such as copper & nickel occur in nature as sulfide ores. In these smelters, ores are reduced to free metals.

16. First step in the process is to remove the sulfur from the sulfide (roasting). The Smelting Process

19. Acid Rain Is Not a New Phenomenon First recognized by Robert Angus Smith in the mid-1800s in Great Britain In the 1950s Swedish scientists began to observe pH values of precipitation lower than 5.2. In the 1960s low pH values were discovered in the north Eastern U.S.

21. Isopleths of annual rainfall pH 1955-56 & 1965-66

22. Isopleths of annual rainfall pH 1972-73 & 1975-76

24. Note the increased concentration from west to east.

25. Inputs of NO x to Norway 1985-93

26. Inputs of SO x to Norway 1985-93

27. Effects of Acid Rain

29. Effects on Aquatic Life In late 1960s –fish populations were found to be declining in lakes in the Adirondack Mountains. –Fish populations were declining in lakes in Sweden & Norway –Salamander populations were declining rapidly in the northeastern U.S.

32. Precipitation pH Data for Dec. 23, 1997-Jan 20, 1998 New York State

33. Effects on Aquatic Life By 1970s in Adirondack Mountains –more than 50% of lakes >600 meters had pH<5 –90% of lakes contained no fish By 1990s in Sweden –14,000 lakes unable to support lake organisms sensitive to acidic conditions –2,200 lakes nearly lifeless

34. Neutralization & Acid-sensitivity Different rivers, lakes & soils are not equally affected by or sensitive to acid deposition. Natural water bodies may contain substances that buffer the pH. The buffering capacity is mainly determined by the amount of bicarbonate (HCO 3 - ) and carbonate (CO 3 2 -) in the water.

35. Natural Buffers If soils and the underlying rock are rich in calcium carbonate (limestone), then the deposited acids are partially neutralized. CaCO 3 + H 2 SO 4 Ca 2+ +SO 4 2- + HCO 3 - + H + This leads to a delay in the acidification of these aquatic systems.

36. Natural Buffers Natural waters underlain by rocks containing little CaCO 3 are more susceptible to acidification. –Adirondacks –Fennoscandinavian region Rocks rich in silicate minerals are abundant in these areas.

39. Human Intervention Sweden & Norway are carrying out a program to neutralize the acid in lakes by adding lime to the lakes. Stimulates the natural process involving the reaction of acid with carbonate. An expensive temporary cure. Analogous to taking antacid tablets to neutralize stomach acid!

40. Effects on Forest Ecosystems Forest damage has been extensive in Europe. In Germany, the 75% of the fir trees were found to be affected in 1983.

41. Declining Forests The crown density of the spruce at right is normal. The crown density of tree at left is lower

42. Declining Forests Leaves and needles can be damaged directly Trees damaged indirectly by loss of nutrients from the soil via leaching. –In very acidic conditions, Al becomes soluble & is released from soil –at high concentration it is toxic & damages roots

45. Destruction of Our History Both SO 2 and acid rain react with buildings, statues & monuments made of limestone & marble. Calcium carbonate is the chemical composition of these materials.

46. Reactions of CaCO 3 Calcium carbonate dissolves in acid rain CaCO 3 (s) + H + (aq) Ca 2+ (aq) + HCO 3 - (aq) Calcium carbonate reacts with SO 2 to form gypsum (CaSO 4.2H 2 O) which is also water soluble.

47. German sandstone statue from 1702 photographed in 1908 (left) & in 1969 (right).

48. Gargoyles