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Acid Rain

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Title: Acid Rain


1
  • Acid Rain

2
Origins of Acid Rain
3
Unpolluted Rainwater
  • Pure water has a pH of 7.0 (neutral)
  • Natural, unpolluted rainwater actually has a pH
    of approximately 5.6
  • The slight, natural acidity of rainwater results
    from the presence of carbon dioxide (CO2) within
    the atmosphere due to the carbon cycle.
  • Once within the atmosphere, the CO2 vapor
    dissolves within the condensed water droplets
    within clouds and forms carbonic acid (H2CO3), a
    weak acid, which dissociates forming the
    hydronium ion (H) and makes the solution
    slightly acidic.

4
Calculation of pH of Unpolluted Rainwater
  • If we know the concentration of CO2 within the
    atmosphere, we can calculate the pH of natural,
    unpolluted rainwater.
  • According to NASA, the current concentration of
    carbon dioxide within the troposphere is
    approximately 380 ppmv.
  • Henrys Law Constant (Hx)- describes the
    distribution of a species between the gaseous and
    aqueous forms due simply to the physical
    solubility of the gas. In effect, it is the
    equilibrium constant for the following
    expression
  • Where PX is the partial pressure of the gas.
    Henrys Law Constants are in ( M atm-1 ).
  • For the equilibrium between gaseous and aqueous
    CO2, Henrys Law Constant would be
  • ppmv parts per million volume

5
Calculation of pH of Unpolluted Rainwater (cont.)
  • To find the partial pressure of the CO2, we use
    the following equation
  • For approximation purposes, we will assume that
    the total pressure is 1 atm (atmospheric pressure
    at sea level) since we are dealing solely with
    the troposphere and the change in atmospheric
    pressure as you increase in altitude within the
    atmosphere will be relatively small.
  • From literature values of Henrys Law Constant,
    we know that
  • Thus, since we know both the partial pressure and
    Henrys Law Constant for CO2, we can solve for
    the concentration of dissolved CO2.

6
Calculation of pH of Unpolluted Rainwater (cont.)
  • For estimation purposes, we can assume that
  • Now that we know the concentration of carbonic
    acid we can use ICE to determine the pH of
    unpolluted rain.
  • Since the second dissociation constant is very
    small in comparison to the first dissociation, in
    estimating the pH of unpolluted rainwater, we
    will discard the second dissolution as having a
    negligible effect on the overall pH. In order to
    determine the pH of unpolluted rainwater, we will
    use the first dissociation constant and ICE.

7
Calculation of pH of Unpolluted Rainwater (cont.)
8
Reasons for Concern
  • Rainwater with increased acidity is often dubbed
    by the popular term acid rain. Scientifically
    we refer to this as acid deposition.
  • Over the past three decades (starting in Europe
    and in particular the Scandinavian countries)
    scientists have observed rain, clouds, and fogs
    with much higher acidities (decreased pH) than
    the natural unpolluted pH of 5.6.
  • Currently, rain with pH values of approximately
    4.5 is very common worldwide.
  • Even more disturbing, clouds with a pH in the
    mid-2 range and fogs with a pH as low as 1.69
    were observed in 1983 and 1993 respectively by
    researchers (Pitts 295).
  • Although 5.6 to 4.5 seems like a small increase
    in acidity, remember that the pH scale is a
    logarithmic scale. Thus, although the pH changes
    by 1.1, the hydrogen ion concentration increases
    by a factor of .

9
Weighted Mean pH of Rain for 2004 Compiled by the
National Atmospheric Deposition Program
10
Overview of Causes
  • Historically, the major acids believed to
    contribute to acid deposition within the
    troposphere have been sulfuric acid (H2SO4) and
    nitric acid (HNO3), which are formed from the
    oxidation of sulfur dioxide (SO2) and oxides of
    nitrogen respectively. Increased levels of sulfur
    dioxide and oxides of nitrogen within the
    troposphere are a direct result of industrial
    combustion.
  • Recently, researchers have been investigating the
    role of organic acids and nitrous acid (HNO2) in
    the formation of acid rain. However, since these
    are new factors (their contributions to the
    overall acidity of rain have not yet been well
    established) and only weak acids (they can only
    contribute a small amount to the acidity of
    rainwater) we will focus on sulfuric acid and
    nitric acid as the main causes of acid
    deposition.

11
Emission of Sulfur Dioxide
  • Sources of Sulfur Dioxide Emissions
  • Natural Sources
  • Volcanic Activity produces SO2
  • Biological Decay produce dimethyl sulfide which
    is later oxidized to SO2 in the atmosphere
  • Anthropogenic (Man-made) Sources
  • High temperature combustion of sulfur containing
    fossil fuels for industrial processes, the
    generation of electricity, and fuel consumption
    (such as that in cars and airplanes).

12
Oxidation of Sulfur Dioxide to an Acid (Gas Phase)
  • 2 main ways with which sulfur dioxide (SO2) is
    oxidized to an acid within the atmosphere
    oxidation in the gas phase and oxidation in the
    aqueous phase
  • Oxidation in the Gas Phase
  • Sulfuric Acid (H2SO4) is a diprotic strong
    acid.

13
Oxidation of Sulfur Dioxide to an Acid (Aqueous
Phase)
  • Oxidation in Aqueous Phase
  • The bisulfite ion (HSO3-) is then oxidized within
    the cloud by the following oxidizing agents to
    form the bisulfate ion (HSO4-), which is the
    product resulting from the first dissociation of
    sulfuric acid.
  • Ozone (O3)
  • Oxygen Gas
  • (Catalyzed by Fe3, Mn2)
  • Hydrogen Peroxide
  • The bisulfate ion can then dissociate

14
Emission of Oxides of Nitrogen
  • Sources of Oxides of Nitrogen
  • NOx (NO NO2)
  • Natural Sources
  • Lightning
  • Biomass combustion (forest fires)
  • Biological Processes
  • Anthropogenic (Man-made) Sources
  • High temperature combustion processes (industrial
    activity, the generation of electricity, and fuel
    consumption), NO is the majority of the product
    (a small amount of NO2 is produced as well)

15
Formation of Nitric Acid
  • Formation of NO2 from NO
  • Reaction with hydroperoxy
  • Reaction with alkyl peroxy
  • Formation of Nitric Acid from NO2
  • Dissociation of Nitric Acid

16
Neutralization by Ammonia
  • Ammonia (NH3) is the only gaseous base present
    within the atmosphere in significant
    concentrations, and thus plays an important part
    in neutralizing atmospheric acids.
  • Sources of Ammonia
  • Livestock waste
  • Fertilizers
  • Industrial processes
  • Natural processes within the soil
  • Burning of agricultural waste
  • Vehicles equipped with 3-way catalysts
  • Neutralization

17
Environmental Effects of Acid Rain
18
Effects of the Acid RainEcosystem
  • Food Pyramid
  • As acid rain moves to the water shield, aluminum
    is released from soils into the streams
  • As pH gets lower, the aluminum level increases
  • Maintaining Osmoregulation is key to survive

19
Forest system
  • the buffering capacity of the soil may neutralize
    some or all of the acidity that had fallen to the
    forest floor
  • more thicker the soil is more resistance to the
    acid rain
  • vital nutrients get neutralize by the acid rain
  • It is same thing for the other plants as well

20
Neutralization of Aluminum
  • Al(OH)3 H2SO4 ? Al(SO4)2 H2CO3
  • Sulfuric acid reacts with the aluminum hydroxide
  • Aluminum gets released from the soil particles in
    this reaction

21
Human Health
  • acid rain feels, tastes, and looks like clean
    rain
  • Sulfur Dioxide Nitric Oxide ? a mixture of very
    tiny liquids and soil particles
  • By inhaling aerosols, it enter through the lungs
    and are easily retained
  • Affect through what we eat

22
Effect of the buildings
  • Damaging buildings that is made up of limestone
    and marble
  • CaCO3(s) 2H(aq) Ca2(aq) CO2(g) H2O
  • Lose details
  • calcium ion and forms gypsum crust over the
    marble or limestone
  • Ca2 SO42- 2H2O  CaSO4  2H2O

23
Original Damaged
24
  • Ways to Counteract

25
Reducing SO2 Emission
  • Scrubbers
  • ex. Wet Scrubbers
  • CaCO3 SO2 H2O O2 -gt CaSO3 CaSO4 CO2
    H2O
  • Fluidized Bed Combustion (FBC)
  • Contains limestone that gets reduced into the
    fuel
  • The heat removed by the flue gas leaves
  • waste solids get disposed

26
  • Up to 95 reduction of SO2

27
SO2 emissions
  • Burning natural gas- creates less SO2 than
    burning coal
  • Using coal containing less sulfur
  • High-sulfur coal- covered with sea water
  • Low-sulfur coal- covered with fresh water

28
Reducing Nitrogen Oxide
  • Overfire Air
  • Transform a fraction of the total air into the
    combustion
  • It moves ammonia gas to the catalytic reaction
    chamber
  • 4NO 4NH3 O2 -gt 4N26H2O
  • 2NO2 4NH3 O2 -gt 3N2 6H2O
  • the safe nitrogen gets in the atmosphere

29
Nitrogen oxide to Nitrogen gas
  • It can be reduced by fitting catalytic converters
    in cars
  • can be done by combustion (substance combining
    with oxygen to release energy)
  • Nitrogen oxides burners reduce up to 30

30
Catalytic Converters
  • Reduction Catalyst
  • Convert NOx to Nitrogen and Oxygen
  • 2NO ? N2O2
  • 2NO2 ? N22O2
  • Oxidation Catalyst
  • 2CO O2 ? 2CO2
  • C5H12(hydrocarbon) 8O2 ? 5CO2 6H2O

31
Using Alternative Energy Source
  • electricity is not limited to fossil fuels
  • nuclear power
  • hydropower
  • wind energy
  • Geothermal energy
  • solar energy
  • Most widely used- nuclear and hydropower
  • For automobile
  • Natural gas powered vehicles
  • batter powered cars
  • Cheapest- Nuclear hydropower and coal

32
Restore a damaged environment
  • Lime can be added to lakes to reduce the acid in
    the lakes and streams
  • less in United States than Norway and Sweden
  • Benefits It reduces acid to prevent pollution
  • Disadvantages It only lasts for short amount of
    time and it has to be repeated in many times.

33
Liming in soil
  • Al3 H2O ----gt Al(OH)2 HAl(OH)2 H2O
    ----gt Al(OH)2 HAl(OH)2 H2O ----gt Al(OH)3
    H
  • Al3 hydrolyze (decompose by reacting with water)
    ----gt generates H
  • Adding lime to neutralize the H

34
Saras Sources
  • Finlayson-Pitts, Barbara and James N. Pitts, Jr.
    Chemistry of the Upper and Lower Atmosphere
    Theory, Experiments, and Applications. San Diego,
    CA Academic Press, 2000.
  • Chapter 2 Processes Linking NOx, SO2, NH3, and
    VOCs to Secondary Particle Formation. Complete
    Report Precursor Contributions to Ambient Fine
    Particulate Matter in Canada. 18 December 2002.
    Meteorological Service of Canada (MSC). 20 March
    2006.
  • lthttp//www.msc-smc.ec.gc.ca/saib/smog/pm_full/pm
    2_5_full_pg2_e.html2.0gt
  • Hydrogen Ion Concentration as pH from
    Measurements Made at the Field Laboratories,
    2004. Isopleth Maps. 2005. National Atmospheric
    Deposition Program (NADP). 20 March 2006.
    lthttp//nadp.sws.uiuc.edu/isopleths/maps2004/phfie
    ld.gifgt
  • Blasing, T.J. and Sonja Jones. Current
    Greenhouse Gas Concentrations. February 2005.
    Carbon Dioxide Information Analysis Center
    (CDIAC). 20 March 2006. lthttp//cdiac.ornl.gov/pns
    /current_ghg.htmlgt

35
Saras Sources (cont)
  • Characteristics of Gases. US Environmental
    Protection Agency. 1 March 2006. US Environmental
    Protection Agency (EPA). 20 March 2006.
    lthttp//www.epa.gov/eogapti1/module2/concentrate/c
    oncentrate.htmgt
  • Schnabel, Ronald R, et al. Acid Rain.
    AccessScience. 9 July 2001. McGraw-Hill
    Encyclopedia of Science and Technology Online. 20
    March 2006. lthttp//www.accessscience.com/server-j
    ava/Arknoid/science/AS/Encyclopedia/0/00/Est_00476
    0_frameset.html?qqqf780ae38-ea8a-4f29-8de7-8a9f
    998fcb6cgt

36
Janices Sources
  • Acid rain's effect on plants and wildlife. 2002.
    eSSORTMENT. 20 Mar. 2006
  • lthttp//ks.essortment.com/acidraineffect_rqmz.htm
    gt
  • Acid Rain. March 1st, 2006. Environmental
    Protection Agency. 18 Mar. 2006.
    lthttp//www.epa.gov/acidrain/gt
  • Acid Rain 21.02.2006. Environmental Science
    Published for everybody round the earth 18.Mar.
    2006 lthttp//www.atmosphere.mpg.de/enid/6320c8eb36
    c377e515d72b1c8dbd3612,0/basics/3__Acid_Rain_3v2.h
    tmlgt
  • Clean coal technologies IEA Clean Coal Centre
    18.Mar. 2006 lthttp//www.iea-coal.org.uk/content/d
    efault.asp?PageId87gt

37
Janices Sources (cont)
  • Kevin_McCue. January 27, 2003. Car Chemistry The
    Catalytic Converter. 17 Mar 2006.
    lthttp//www.chemistry.org/portal/a/c/s/1/feature_e
    nt.html?id9a4f4f92320b11d7f4a56ed9fe800100gt
  • SARN PHAMORNSUWANA. 1/15/99. CAUSES, EFFECTS, AND
    SOLUTIONS OF ACID RAIN. 21.Mar 2006
    lthttp//www.geocities.com/CapeCanaveral/Hall/9111/
    DOC.HTMLHUMANSgt
  • Robert Jacobson. Water No longer Taken For
    Granted. Texas Thomson Gale, 2006
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