4. Contents Review of pH Definition of acid rain
Pollutants that create acid rain:
a. sulfur dioxide
b. nitrogen oxide
c. ammonia
IV. Acid rain ecosystem impacts
V. Other impacts
VI. Legislation and technology
VII. Trends over time

5. I. Review of pH
pH is a measure of the activity of hydrogen ions (H+) in a solution.
pH is shorthand: pH = -log10 [H+]
- a small p is used in place of writing -log10
- H represents the concentration of hydrogen ions ([H+])
Acid Rain 101

6. 1.Review of pH Water is converted into hydrogen and hydroxyl ions.
H2O  H OH-
water hydrogen ion hydroxyl ion
When the activity of these ions is equal, water is neither acidic or alkaline and is said to be neutral, represented by a pH value of 7.
When the activity of hydrogen ions is greater, a solution is said to be acidic and is represented by a range of pH values from 0-6.
When the activity of hydroxyl ions is greater, a solution is said to b alkaline and is represented by a range of pH values from 7-14.

7. 1.Review of pH
Because pH is a logarithmic function, there are tenfold differences between each pH value.
Examples:
- A pH value of 6 is ten times more acidic than a pH value of 7.
- A pH value of 5 is one hundred times more acidic than a pH value of 7.

8. 1.Review of pH
In 1997, the pH of wet deposition at HBEF was 4.2; today it is 4.5.
From Acid Rain Revisited, page 5

9. II. Definition of Acid Rain
pH levels found in precipitation
Acid rain
Average pH of rain at Hubbard Brook Experimental Forest in 2007
< 5.2
4.5
Acid Rain 101

10. Acid rain isn’t just RAIN-
2. Definition of Acid Rain
Acid rain isn’t just RAIN-
It includes everything that falls from the atmosphere (with a pH < 5.2):
- Wet precipitation (rain, snow, etc.)
- Dry dust and gases (dry deposition)
- Clouds and fog
The terms “acid deposition” and “acid precipitation” are more descriptive, but “acid rain” is widely used and accepted.

11. III. Pollutants that Cause Acid Rain
What creates acid rain?
- sulfur dioxide
- nitrogen oxides
- ammonia
Acid Rain 101

12. 3. Pollutants that cause acid rain
Sulfur dioxide, emitted mainly from combustion of coal and oil in factories and powerplants.

13. Chemical reactions: sulfur dioxide
3. Pollutants that cause acid rain
Chemical reactions: sulfur dioxide
Coal and oil contain sulfur. When burned in factories and powerplants, the sulfur combines with oxygen in the air and is emitted from smokestacks and chimneys.
S + O2  SO2 (sulfur dioxide)
Processes found in chemical and petroleum
industries also release sulfur into the air.

14. 3. Pollutants that cause acid rain
Chemical reactions: sulfur dioxide
SO H2O → H2SO4
sulfur dioxide water → sulfuric acid
H2SO4 ↔ H HSO4- ↔ 2H SO42-
sulfuric acid ↔ hydrogen ions + sulfate
Sulfur dioxide reacts with water in the atmosphere to create sulfuric acid, which dissociates into sulfate and hydrogen ions.
Hydrogen ions make a solution acidic.

15. 3. Pollutants that cause acid rain Nitrogen oxides from
electric utilities
automobiles
Lightening (to a much smaller degree)

16. 3. Pollutants that cause acid rain
Major sources of Nitrogen oxides:
Transportation
≈ 54% nationally
- Uses nitrogen found in atmosphere
Electric Utilities
≈ 30% nationally
- Use nitrogen found in coal and oil
The high temperature of the internal combustion engine- used in autos, airplanes, electric utility boilers, etc releases energy that causes a reaction between nitrogen and oxygen.
Acid Rain 101

17. Nitrogen oxides 3. Pollutants that cause acid rain
Energy + N2 + O2  2NO
Energy + 2NO + O2  2NO2
The transportation sector (cars, trucks, etc..,) is the leading source of nitrogen oxides in the atmosphere.
Electricity generation, which still largely relies on combustion, is the second leading source.
The energy released by the lightning also creates a reaction between oxygen and nitrogen, so it is a natural source of nitrogen oxides to the atmosphere.

18. Chemical reactions: nitrogen oxides
3. Pollutants that cause acid rain
Chemical reactions: nitrogen oxides
NOx H2O → HNO3
nitrogen oxides water → nitric acid
HNO ↔ H NO3-
nitric acid ↔ hydrogen ion + nitrate
Nitrogen oxides react with water in the atmosphere to create nitric acid, which dissociates into nitrate and hydrogen ions.
Hydrogen ions make a solution acidic.

19. 3. Pollutants that cause acid rain
Ammonia (NH3) is produced mainly through agriculture:
livestock and poultry
manure
fertilizer application

20. Chemical reactions: Ammonia
3. Pollutants that cause acid rain
Chemical reactions: Ammonia
Ammonia gas reacts with sulfuric and nitric acids to form ammonium aerosols.
Example: NH NO3-  NH4NO3
ammonium nitrate ammonium nitrate
When aerosols are deposited to the ground they react with oxygen in a process called nitrification.
NH4NO O2  2H NO H2O
ammonium nitrate oxygen hydrogen ions nitrate water
This process releases H+ ions, which lowers the pH (creates more acidic conditions).

21. From emissions to acid deposition:
From Acid Rain Revisited, pg. 4

22. IV. Acid rain ecosystem impacts
1. Acid rain causes increased
loss of base cations from soil
this causes
Decrease in acid neutralizing capacity (ANC) of soils
(reduced ability to buffer the incoming acids)
Lower fertility of soils
(base cations are nutrients necessary for tree growth)
Acid Rain 101

23. How does acid rain affect soils?
4.a. Impacts on terrestrial ecosystems
2. Inorganic aluminum is dissolved from minerals and accumulates in the soil.
this causes
The presence of dissolved inorganic aluminum in soil is harmful to plants as it can damage root tips and affect the way plants take up nutrients.
Dissolved inorganic aluminum is also
toxic to animals that
live in the soil
such as frogs,
salamanders and larval
stages of insects.

24. 4.a. Impacts on terrestrial ecosystems
From Acid Rain Revisited, pg. 10

25. Is it a big problem in terrestrial ecosystems?
4.a. Impacts on terrestrial ecosystems
Is it a big problem in terrestrial ecosystems?
It depends on the soil of the ecosystem. Soils with limestone bedrock, for example, are able to buffer incoming acids. Soils with a low acid neutralizing capacity (ANC), such as granitic bedrock, are not and are called acid-sensitive soils.

26. Changes in the calcium cycle at the Hubbard Brook Experimental Forest between 1950-1995
The amount of available calcium in the soil at the HBEF appears to have declined more than 50 percent between the years 1950 – 1995.
From Acid Rain Revisited, pg. 10

27. 4.b. Impacts on aquatic ecosystems
1. Chemical effects on aquatic systems
Inorganic aluminum dissolves out of minerals at acidic pH levels, and is toxic to living things.
Inorganic aluminum is 1,000 times more soluble in water with a pH of 4.6 than in water with a pH of 5.6.

28. 4.b. Impacts on aquatic ecosystems
1. Chemical effects on aquatic systems
It can reduce the acid neutralizing capacity of water.
Acidic waters are defined as having an ANC of less than zero (i.e., no buffering capacity in the water).
Acid Rain 101

29. 4.b. Impacts on aquatic ecosystems
2. Biological effects:
Animals all along the food chain are affected: zooplankton, invertebrates and fish can be harmed.
Aluminum clogs fish gills by forming lesions that obstruct a fish’s ability to take oxygen from water.

30. From http://www.epa.gov/acidrain/effects/surface_water.html
4.b. Impacts on aquatic ecosystems
2. Biological effects on animals:
Different organisms can tolerate different pH levels. For example, frogs are the only organisms included on this chart that can tolerate a pH of 4.0.
From

31. 4.b. Impacts on aquatic ecosystems
≈ 8% of lakes in Adirondacks
≈ 15% of lakes in New England
and
≈ 8.5% of streams in the northern Appalachian Plateau
are considered acidic, which means ANC is less than zero.
Acid Rain 101

32. V. Other Impacts from acid rain
Causes damage to certain building materials, historical monuments, ancient statues and gravestones.
Sulfuric acid in the rain chemically reacts with calcium compounds in the stones (limestone, sandstone, marble and granite) to create gypsum, which then flakes off.
Acid Rain 101

33. 5. Other impacts from acid rain
Causes an increased rate of oxidation for iron.
Visibility is reduced by sulfate and nitrate in the atmosphere.

34. What has been done to remedy the problem of acid rain?
VI. Legislation and technology
What has been done to remedy the problem of acid rain?
In the past 30 years, the U.S. Congress has enacted several laws to promote clean air. Two important laws were the Clean Air Act of 1970 and the Clean Air Act Amendments of 1990.
Acid Rain 101

35. 6. Legislation and technology The Clean Air Act of 1970
Was not written to reduce acid rain, but to reduce pollutants in the air in general.
Identified six major pollutants as harmful to human health and environment:
Carbon monoxide
Sulfur dioxide
Ozone
Nitrogen dioxide
Lead
Particulate matter*
* With size of particle less than or equal to 10 micrometers

36. Title IV of the Clean Air Act Amendments of 1990
6. Legislation and technology
Title IV of the Clean Air Act Amendments of 1990
Targeted the emissions of electric utilities, which accounted for 70% of sulfur and 30% of nitrogen emissions.
Goals:
- reduce SO2 by 10 million tons, or 40%
- reduce NOx by 2 million tons, or 10%
compared to 1980 levels

37. Some strategies used to reduce sulfur and nitrogen oxides emissions:
6. Legislation and technology
Some strategies used to reduce sulfur and nitrogen oxides emissions:
‘cap,’ or limit, the amount of SO2 that can be emitted by electric utilities
use of trade allowances for SO2
use of catalytic converters in automobiles

38. Some strategies used to reduce sulfur and nitrogen oxides emissions:
6. Legislation and technology
Some strategies used to reduce sulfur and nitrogen oxides emissions:
use of ‘clean coal technology’ (use of low sulfur coal in factories and electric utility plants)
Installation of scrubbers in smokestacks

39. How do scrubbers work?
Generally, a scrubber is tower equipped with a fan that extracts gases from the power plant into the tower.
A limestone slurry is injected into tower to mix with these gases.
Calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from scrubber.
A type of scrubber called ‘Counter Current Packed Tower’, sold by Ceilcote Air Pollution Control

40. How do catalytic converters work?
Catalytic converters treat exhaust before it leaves the car and remove a lot of the pollution.
US car manufacturers were required to reduce the amount of emissions coming from vehicles by installing catalytic converters.

41. To date there is no legislation to:
6. Legislation and technology
To date there is no legislation to:
‘cap’ NOx emissions from electric utilities, which will likely increase as electric generation from power plants increases
set standards for ammonia emissions.
Have the CAA and CAAA helped to reduce SO2 and NOx pollution?

42. Change in SO2 emissions in the U.S. over time
VI. Legislation and technology
Change in SO2 emissions in the U.S. over time
Total SO2 emissions (US)
1940: 20 million tons
1970: 28 million tons
2002: 19 million tons
SO2 emissions from utilities (US)
1980: million tons
2002: million tons
Acid Rain 101

43. 6. Trends over time
Sulfate
1994
2005

44. 6. Trends over time
Concentration of Sulfate in Precipitation at the Hubbard Brook Experimental Forest
Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.

45. Change in NOx emissions in the U.S. over time
6. Trends over time
Change in NOx emissions in the U.S. over time
NOx emissions from utilities (US)
1990: 5.5 million tons
2001: 4.7 million tons
Acid Rain 101

46. 6. Trends over time
Nitrate
1994
2005

47. 6. Trends over time
Concentration of Nitrate in Precipitation at the Hubbard Brook Experimental Forest
Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.

48. 6. Trends over time
Ammonium
1994
2005

49. 6. Trends over time
Concentration of Ammonium in Precipitation at the Hubbard Brook Experimental Forest
Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.

50. 6. Trends over time
Have reductions in SO2 and NOX affected the acidity, or pH of precipitation?

51. 6. Trends over time
Acidity (pH)
1994
2005

52. 6. Trends over time
pH of Stream Water and Precipitation at the Hubbard Brook Experimental Forest
Note: An increase in pH indicates a decrease in acidity.
Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.

53. Overall… 6. Trends over time
Sulfur dioxide regulation has been fairly successful. However, emissions remain high compared to background (pre-industrial) conditions.
Although emissions of NOx and ammonia have not been fully addressed, nitrogen deposition has declined significantly over the past decade as electric utility regulations take effect.

54. A complex, tricky problem…
6. Trends over time
A complex, tricky problem…
Sulfur and nitrogen compounds can travel thousands of kilometers from their original source, therefore
Air pollution crosses state and national boundaries. (ie: Pollutants from power plants in Michigan or New Jersey can travel to the forests of New Hampshire and Vermont.)
Taller smokestacks have improved air quality in industrialized areas, but now pollutants are blown great distances by wind and affect much larger areas.

55. Clean Air Interstate Rule
6. Trends over time
Clean Air Interstate Rule
Designed to reduce air pollution that moves across state boundaries
Will cap SO2 and NOx emissions across 28 eastern states and the District of Columbia.
When fully implemented…
-will reduce SOx by 70% from 2003 levels
-will reduce NOx by 60% from 2003 levels

56. States Covered by Clean Air Interstate Rule
6. Trends over time
States covered by Clean Air Interstate Rule
From

57. World-wide 6. Trends over time
Acid rain is a substantial problem wherever there is concentrated industry, particularly in
-People’s Republic of China
-Eastern Europe
-Russia
A number of international treaties dealing with the long-range transport of atmospheric pollutants have been signed.
Sulfur Emissions Reduction Protocol
Convention on Long-Range Transboundary Air Pollution

58. The Hubbard Brook Acid Rain Story
For more information on the role of the Hubbard Brook Ecosystem Study in acid rain research, please view the next slideshow.
The Hubbard Brook Acid Rain Story
Part 1: The Discovery