What is meant by Acid Rain by yantingting

VIEWS: 12 PAGES: 58

									               Contents
I.   Review of pH
II.  Definition of acid rain
III. 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
                 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
 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.
 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.
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
                II. Definition of Acid Rain

      pH levels found in precipitation

      Acid rain                       < 5.2

      Average pH of rain at            4.5
      Hubbard Brook
      Experimental Forest in
      2007


Acid Rain 101
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.
     III. Pollutants that Cause Acid Rain

           What creates acid rain?
     - sulfur dioxide     - nitrogen oxides
                          - ammonia




Acid Rain 101
 3. Pollutants that cause acid rain
•Sulfur dioxide, emitted
mainly from combustion of
coal and oil in factories and
powerplants.




                                  www.FreeFoto.com
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)   http://en.wikipedia.org/wiki/Image:Gavin_Plant.JPG



• Processes found in chemical and petroleum
  industries also release sulfur into the air.
  3. Pollutants that cause acid rain
    Chemical reactions: sulfur dioxide
      SO2 +          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.
3. Pollutants that cause acid rain
        Nitrogen oxides from




  electric utilities                                    automobiles




                                                               www.FreeFoto.com
                Lightening (to a much smaller degree)
 3. Pollutants that cause acid rain
 Major sources of Nitrogen oxides:

Transportation                  Electric Utilities
  ≈ 54% nationally                 ≈ 30% nationally
  - Uses nitrogen found in         - Use nitrogen found
      atmosphere                       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
 3. Pollutants that cause acid rain
              Nitrogen oxides
             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.
 3. Pollutants that cause acid rain
   Chemical reactions: nitrogen oxides

     NOx            +     H2O → HNO3
     nitrogen oxides +    water    →   nitric acid

     HNO3           ↔       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.
  3. Pollutants that cause acid rain


Ammonia (NH3) is
produced mainly
through agriculture:
• livestock and poultry
• manure
• fertilizer application
                             www.FreeFoto.com
  3. Pollutants that cause acid rain
        Chemical reactions: Ammonia
• Ammonia gas reacts with sulfuric and nitric acids
  to form ammonium aerosols.
  Example:   NH4+    +   NO3-               NH4NO3
         ammonium        nitrate            ammonium nitrate

• When aerosols are deposited to the ground they
  react with oxygen in a process called nitrification.
  NH4NO3    +        2O2    2H+ +             2NO3- + H2O
  ammonium nitrate   oxygen hydrogen ions      nitrate water


• This process releases H+ ions, which lowers the
  pH (creates more acidic conditions).
From emissions to acid deposition:




              From Acid Rain Revisited, pg. 4
        IV. Acid rain ecosystem impacts

             1. Acid rain causes increased
             loss of base cations from soil
                             this causes




Decrease in acid neutralizing              Lower fertility of soils
  capacity (ANC) of soils                  (base cations are nutrients
  (reduced ability to buffer the           necessary for tree growth)
        incoming acids)

 Acid Rain 101
 4.a. Impacts on terrestrial ecosystems
 How does acid rain affect soils?
    2. Inorganic aluminum is dissolved from
      minerals and accumulates in the soil.

                              this causes


The presence of                             Dissolved inorganic
dissolved inorganic                         aluminum is also
aluminum in soil is                         toxic to animals that
harmful to plants as it can                 live in the soil
damage root tips and                        such as frogs,
affect the way plants take                  salamanders and larval
up nutrients.                               stages of insects.
4.a. Impacts on terrestrial ecosystems




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



Is it a big problem
    in terrestrial
   ecosystems?

                                                   www.FreeFoto.com



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.
 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
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.
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
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          www.FreeFoto.com

  from water.
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 http://www.epa.gov/acidrain/effects/surface_water.html
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
                    Acid than
              is less Rain 101 zero.
             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.
www.Free.Foto.com


                        Acid Rain 101
5. Other impacts from acid rain
  • Causes an                  • Visibility is reduced by
  increased rate of              sulfate and nitrate in
  oxidation for iron.            the atmosphere.




            www.FreeFoto,com                 www.FreeFoto.com
           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
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
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
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
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
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           A type of scrubber
limestone produces pH-neutral        called ‘Counter Current
                                     Packed Tower’, sold by
calcium sulfate that is physically   Ceilcote Air Pollution
removed from scrubber.               Control
 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.
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?
     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: 17.5 million tons
 •2002: 10.3 million tons
                       Acid Rain 101
6. Trends over time

             Sulfate




      1994             2005
6. Trends over time
  Concentration of Sulfate in Precipitation
 at the Hubbard Brook Experimental Forest
                             100

                                      Sulfate
                              80
     Concentration (µeq/L)




                              60



                              40



                              20



                               0
                               1960   1965   1970   1975   1980   1985   1990   1995   2000     2005      2010

                                                             Water Year
  Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.
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
6. Trends over time

             Nitrate




      1994             2005
6. Trends over time
   Concentration of Nitrate in Precipitation
  at the Hubbard Brook Experimental Forest
                              50

                                      Nitrate
                              40
      Concentration (µeq/L)




                              30



                              20



                              10



                               0
                               1960   1965   1970   1975   1980   1985   1990   1995   2000   2005   2010

                                                             Water Year
    Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.
6. Trends over time

           Ammonium




      1994            2005
6. Trends over time
 Concentration of Ammonium in Precipitation
 at the Hubbard Brook Experimental Forest
                              50

                                      Ammonium
                              40
      Concentration (µeq/L)




                              30



                              20



                              10



                               0
                               1960   1965   1970   1975   1980   1985   1990   1995   2000   2005   2010

                                                             Water Year
   Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.
6. Trends over time


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

          Acidity (pH)




      1994               2005
6. Trends over time
      pH of Stream Water and Precipitation
   at the Hubbard Brook Experimental Forest
              5.2

                        Streamwater pH
              5.0

              4.8
                                                           1984 (slope of line becomes significant)
              4.6
         pH




              4.4
                        Precipitation pH
              4.2

              4.0

              3.8
                 1960     1965     1970    1975     1980     1985    1990     1995      2000     2005   2010

                                                       Water Year
    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.
6. Trends over time

                Overall…
• 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.
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.
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
6. Trends over time
 States covered by Clean Air Interstate Rule




                                From www.epa.gov
6. Trends over time
                  World-wide
 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
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

								
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