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Lecture 13

 

Conventional Hydrocarbons

 

•         Coal: 1037x1012 kg

•         Oil: 1033.1x109 bbl

•         Gas: 5141.6 TCF

 

•         Total: 4.02x1022J

•         World use today: 4.1x1020J/yr

•         In 2040: ~ 7.2x1020 J/yr

•         ΰ Hydrocarbons will last > 30 years

 

Thoughts on Hydrocarbons

 

•         World economy is based on use of hydrocarbons

•         Strong indications that conventional hydrocarbons will be available for the near future (30 years or more)

•         Addition of large resources possible by utilizing unconventional hydrocarbons

ΰ End of hydrocarbon dependence will not come due to lack of reserves

ΰ Environmental considerations need to drive the decision

 

Consequences of Hydrocarbon Use

•         Mining:

–        Disruption of surface

–        Mining accidents

–        Acid run off

•         Burning ΰ Main topic here

•         Life quality choices

–        Building of Roads

–        Sprawl

 

Consequences of combustion of fossil fuels

  1. Release of Greenhouse Gases  ΰ Inevitable
  2. Pollution

–        Acid Rain

–        Particulates

–        Toxic Metals

ΰ Removal possible

  1. Release of Waste Heat

ΰ Common to all energy production based on heat cycle

 

Origin of pollutants (Fig. 1)

 

Ozone

•         Ozone O3 is present in two locations

•         Stratosphere ΰ’Good ozone’

–        Prevents ultraviolet radiation from reaching the Earth’s surface

–        Interaction with pollutants (CFCs etc.) has decreased the presence of O3 ΰ Ozone hole

–        Depletion of stratospheric ozone not directly related to energy consumption

•         Tropospheric Ozone ΰ ‘Bad Ozone’

–        Ozone is a very strong oxidant ΰ causes damage to organic tissue

–        Contributes to smog ΰ breathing problems

–        Damages leaves etc.

–        Produced by interaction of sunlight with unburned hydrocarbons

 

Acid Rain

 

•         General term for precipitation with pH < 5.5

•         Natural acid rain related to volcanic eruptions

•         Anthropogenic acid rain caused by release of SO2 and NOxΰ fossil fuel burning and smeltering

 

Causes for acidity

 

•         Natural: CO2 + H2O ΰ H2CO3 ΰ H+ + HCO3-

                                                                                    ΰ H+ + CO3--

Carbonic Acid is a weak acid: 1 out of 1000 ionized

Carbonic acid is cause for pH < 7 in natural rain

ΰ    Range: 5.5<pH<7

ΰ    Basic ingredient for natural weathering

 

  • Anthropogenic:
  • Sulfuric Oxides:

S + O2 ΰ SO2

SO2 + ½ O2 ΰ SO3

SO3 + H2O ΰ H2SO4 ΰ sulfuric acid, very active

  • Nitric Oxides:

N + O2 ΰ NO2 ΰ formation fx of temperature

2NO2 + H2O + ½ O2 ΰ 2HNO3 ΰ nitric acid, very active

 

Distribution of acidity reflects production pattern and wind direction (Fig. 2)

 

Changes in releases of SO2 and NOx (Fig. 3)

 

Effects of Acid Rain

•         Direct:

–        Decrease in pH ΰ water becomes more acidicΰ organisms (e.g. fish) cannot tolerate pH < 5 ΰ decrease in fish population in lakes ΰ decrease in organisms ΰ increase in clarity of lake water ΰ deeper penetration of sunlight ΰ increase in bottom covering plants ΰ decrease in spawning areas

 

Changes in pH levels of Adirondack lakes (Fig. 4)

 

•         Indirect (more complicated chain of events, not so well understood)

–        Classification of pollutants

•         Nutrients (Ca; Mg; NH4; NO3)

•         Acids (H2SO4; HNO3; HCl)

•         Toxins (SO2; HF; heavy metals; organic compounds)

 

Possible chain of events

  1. Increased growth due to increased availability of nutrients
  2. Destabilization of soil

•         Leaching of Ca, Mg due to high acidity

•         Relative increase in Al concentration

•         Mobilization of Al (toxic) and heavy metals

  1. Damage to decomposers (bacteria) because of Al toxidity
  2. Internal acid production
  3. Fewer nutrients available, decrease in dissolved organic matter
  4. Warm, dry years increase acidity in deeper root system ΰ damage to plants

 

Buffering

•         Similar to weathering: Example

–        CaCO3 + H2SO4 ΰ H2CO3 + CaSO4

 

•         Reaction with minerals with high concentrations of Ca uses up H+, increases the pH, but also removes Ca from the cycle

–        Example: Limestone, made up mostly of CaCO3

 

Vulnerability to Acid Rain

•         Exchange of H+ for cations (Ca, Mg) increases pH, lowers acidity

•         Exchange is fx of rock solubility and concentration of Ca etc.

–        Igneous rock have low solubility, low Ca concentrations ΰ low buffering capacity

–        Sedimentary rocks have high Ca concentrations ΰ high buffering capacity

•         Difference between Adirondack Mountains and Rochester area

•         ‘Liming of Lakes’ used to increase pH

 

Distribution of vulnerable areas in North America (Fig. 5)