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