Regional and Global Atmospheric Pollution Chapter 14

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Regional and Global Atmospheric Pollution
(Chapter 14)

• Global warming
• Ozone layer destruction
• Nuclear winter
• Acid rain ? Regional
• US-Canada, Sweden-Germany
• Photochemical smog ?Local
• Los Angles

Global
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Atmospheric Chemistry

• Stratospheric chemistry
• Ozone
• Tropospheric chemistry
• Photochemical smog
• Acid rain (precipitation)
• Other atmospheric pollution (PM, Pb, CO)

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I. Greenhouse Effect Global Warming

• Greenhouse effects
• The short-wave radiation of the sun is absorbed
  by the earth, heating it to a temperature of
  about 255oK. Because of the heat it absorbs, the
  earth re-radiates energy back into space in the
  form of long-wave radiation. In the atmosphere,
  however, are molecules that can absorb this
  re-radiated energy, converting it to heat. Being
  heated, the molecules can now also re-radiate the
  heat they absorb back into earth, producing
  perturbation differential temperature of 33K.
  This temperature differential is due to the
  greenhouse effect.

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Greenhouse Gases(Infrared-Absorbing Gases)

• CO2
• Burning of fossil fuel and burning of biomass
  after deforestation, and biomass biodegradation
• Responsible for about half of the atmospheric
  heat retained by trace gases
• Other trace gases
• CH4 (biogenic) CFCs (since 1930s) N2O
  (biogenic)
• On a molecule-for-molecule basis, these gases are
  more effective in trapping heat than CO2
• Water

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Concentration Change and Cause

• CO2
• Increased by 1 ppm/year 260 ppm (preindustrial
  level) to 360 ppm (present time)
• Source (deforestation) vs. sink (photosynthesis
  and ocean absorption)
• CH4
• Increased by 0.02 ppm/year 0.70 ppm
  (preindustrial level) to 1.8 ppm (present time)
• Anthropogenic sources direct leakage of natural
  gases, byproduct emission from coal mining and
  petroleum
• Biogenic sources bacterial activities in
  landfills, rice fields, and digestive tracts of
  ruminant animals

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Relative Contribution to Global Warming

• RIRF Relative Instantaneous Radiative Forcing
• GWP Global Warming Potential

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Index Used in Determining the Factors Influencing
Global Warming

• RIRF (Relative Instantaneous Radiative Forcing)
• RIRF is a measure of the ability of an
  incremental addition of a gas, in the present
  atmosphere, to increase the absorption of
  infrared radiation. The RIRF for CO2 is
  arbitrarily set at 1.
• GWP (Global Warming Potential)
• GWP f (concentration, absorptivity, residence
  time, etc). The GWP describe the long-term
  contribution of any gas by comparison to that of
  CO2.

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Relative Contribution of Gases toGlobal Warming
Potential (GWP)(Lashof and Ahuja, 1990, Nature,
344 (1990)529-31)
(a) In 1985 (b)
Throughout 1980s
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CFCs (CFC-11 and CFC-12)

• CFCs not only will cause ozone depletion, but
  also will contribute global warming
• Empirical equations to predict the
  equilibrium-incremental increase in temperature
  ?T caused by CFCs
• ?T (?Td/ln 2) ln CO2/CO20 0.057(N2O0.5
  - N2O00.5) 0.019 (CH40.5 - CH400.5)
  0.14 (CFC-11 - CFC-110) 0.16(CFC-12 -
  CFC-120
• where ?Td is the equilibrium-incremental change
  in temperature for a doubling in CO2
  concentration and the zero subscripts refer to
  the initial value of the parameter affected. The
  temperature is in degrees Celsius and the
  concentrations are in ppb.

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Prediction of Temperature Increase due to CFC

• Given ?Td (3oC) and the data in the table below
• Calculate the equilibrium-incremental increase in
  temperature from 1850 to 2075 (Answer 4.95oC)
• Calculate the equilibrium-incremental increase in
  temperature from 1985 to 2075 (Answer 3.76oC)

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Prediction of Global Warming

• The physics and chemistry of greenhouse are well
  understood, however, there is great difficulty in
  predicating global warming
• CO2 in 2050 will reach 600 ppm ?????
• A better understanding on the environmental
  chemistry of CO2 (I.e., fate, transport, and
  modeling of CO2 in the global environment) is
  needed

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II. Acid Rain

• Normal rain water in equilibrium with CO2 has a
  pH 5.7 (why?)
• Acid precipitation pH
• acid rain
• acid fog
• acid snow
• acid rime (frozen cloudwater which may condense
  on snowflake or exposed surfaces)

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Typical Values of Ion Concentrations in Acidic
Precipitation (pH 4.25)
H NH4 Ca2 Na Mg2 K
SO42- NO3- Cl-
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Concentrations of Major Constituents of Acid Fog
(pH 3.5) Near the Bay of Fundy, Canada
Cox et al. (1989), Water, Air, and Soil
Pollution, 48263-76
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Composition of Two Fresh Snow Samples
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Reactions Involved In Acid Formation

• Sulfuric acid formation
• SO2 OH ? HOSO2
• HOSO2 (hydrosulfurdioxide free radical)
• HOSO2 O2 ? SO3 HO2
• HO2 (hydroperoxyl free radical)
• SO3 H2O ? H2SO4
• HO2 NO ? NO2 OH
• Nitric acid formation
• OH NO2 ? HNO3

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Control of Anthropogenic Nitrogen and Sulfur
Emission

• Design of better combustion chambers
• more uniform complete combustion in
  fluidized-bed combustion
• Removal of sulfur dioxide from flue gas
• using hydrated lime slurry Ca(OH)2 or limestone
  slurry CaCO3 a process called desulfurization
• Ca(OH)2 SO2 ? CaSO3 H2O
• CaCO3 SO2 ? CaSO3 H2O
• CaSO3 1/2O2 2H2O ? CaSO42H2O
• Conversion of coal to gaseous and liquid forms

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III. Ozone Layer Destruction

• Scientists first expressed concern over the
  possible destruction of the ozone layer in the
  1970s
• CFCs banned by US EPA since 1979
• In 1985, an announcement was made that a big hole
  in stratosphere over Antarctica the size of the
  United States has been created due to ozone
  depletion mostly by CFCs

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Ozone Depletion

• Responsible species (X) X Cl, Br, OH, NO
• Reactions for ozone depletion
• X O3 ? O2 XO
• XO O ? X O2
• Dominant sources
• Chloride
• CH3Cl (natural origin)
• CFCs CFC-11 and CFC-12 are two most important,
  which have lifetime of 60 and 110 years,
  respectively
• CCl4 both natural and man-made origin
• Bromide
• used mostly in fire extinguishers
• OH, NO Diffused from troposphere

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Properties of Common CFCs
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CFCs and Substitutes

• Uses of CFCs
• Aerosol propellants, refrigerants, solvents,
  foamed plastics
• Substitutes (HCFCs) and their ozone depletion
  potential

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CFC Alternatives Their Uses Regulations