Chem

• Atmosphere


  • Temperature varies greatly with altitude
  • The profile makes a Z-shape from mesosphere to the ground

  
• Thermal Stratification of the Atmosphere


  1. Troposphere (0 – 15km)

  2. Stratosphere (15 – 50 km)

  3. Mesosphere (50 – 100 km)

  4. Thermosphere (above 100 km)

  
• Tropopause


  Upper limit of the troposphere, varies between 9 – 16 km depending on latitude and season

  
• Stratosphere


  Contains the stratospheric ozone layer, which (mostly) shields us from harmful UV light

  
• Ionosphere


  Above 60 km, where there is a significant concentration of ions and electrons
• Atmosphere pressure


  • Highest at the surface and decreases with height
  • Fluctuations in pressure are a driving force of weather

  
• Atmospheric composition


  • Lighter gases tend to rise to the top
  • Gases are measured in ppm volume (µL/L), which is directly proportional to mole fraction
• Near the Earth's surface, about 99% of the atmosphere is composed of nitrogen and oxygen
• Oxygen


  Has a much lower bond enthalpy than nitrogen, and is therefore more reactive
• Ultraviolet radiation


  Has enough energy to break chemical bonds

  
• Although the troposphere is made up almost entirely of nitrogen and oxygen, other gases present in relatively small amounts still have a profound effect on the troposphere
• Increasing levels of CO2 in the atmosphere


  Causing an increase in global temperatures
• Greenhouse gases


  • Carbon Dioxide
  • Methane
  • Nitrous Oxide
  • Ozone
  • Chlorofluorocarbons
• Photochemistry


  1. Photodissociation

  2. Photoionization
• Ozone


  • Absorbs much of the radiation between 240 and 310 nm
  • Forms from reaction of molecular oxygen with the oxygen atoms produced in the upper atmosphere by photodissociation (< 242 nm)

  
• Rowland and Molina (Nobel Prize, 1995) discovered that chlorine from chlorofluorocarbons (CFCs) may be depleting the supply of ozone in the upper atmosphere

  
• Chlorofluorocarbons (CFCs)


  • Used for years as aerosol propellants and refrigerants
  • Not water soluble and quite unreactive
• Ozone depletion by CFCs


  1. The C—Cl bond is easily broken when the molecule absorbs radiation with a wavelength between 190 and 225 nm

  2. The chlorine atoms formed react with ozone: Cl + O3 ⎯⎯→ ClO + O2

  
• In spite of the fact that the use of CFCs in now banned in over 100 countries, ozone depletion will continue for some time because of the tremendously unreactive nature of CFCs
• Primary air pollutants


  Released directly from planet's surface, e.g. dust, smoke particles, Nitrogen, Carbon
• Secondary air pollutants


  Formed when primary pollutants react or combine with one another, or basic elements
• Carbon Monoxide


  • Produced when organic materials are incompletely burned
  • Binds to hemoglobin in blood and makes the hemoglobin less able to carry oxygen
  • Most dangerous in enclosed spaces
• Carbon monoxide binds preferentially to the iron in red blood cells, exposure can lower O2 levels to the point of causing loss of consciousness and death
• Volatile Organic Compounds


  • Hydrocarbons - Group of organic compounds consisting of carbon and hydrogen
  • Evaporated from automobile fuel or remnants of fuel incompletely burned
• Particulates


  • Minute pieces of solid materials dispersed into the atmosphere (<10 microns), e.g. smoke, asbestos, dust, ash
  • Can accumulate in lungs and interfere with the ability of lungs to exchange gases
• Sulfur Dioxide (SO2)


  • Sulfur and oxygen compound produced when sulfur-containing fossil fuels are burned
  • Reacts with moisture in the air to form sulfuric acid
  • Primarily responsible for acid rain
• Acid rain


  Causes corrosion in building materials, reacting with calcium carbonate in marble and limestone
• Removing SO2


  Injecting powdered limestone which is converted to calcium oxide, CaO reacts with SO2 to form a precipitate of calcium sulfite
• Nitrogen Oxides (NOx)


  • Formed when combustion takes place in the air
  • Automobile exhaust is primary source
  • NOx is also a precursor to acid rain and photochemical smog
• Nitrogen Dioxide (NO2)


  • Forms from the oxidation of nitric oxide, NO, a component of car exhaust
  • Recognized as smog, that brownish gas that hangs above large cities
• Secondary air pollutants


  • Ozone (O3), PANs (Peroxyacetyl nitrate), Aldehydes
  • Formed by interaction between NOx and VOCs
• Photochemical smog


  • Brown-air smog formed when some primary pollutants react under the influence of sunlight, including NOx, O3, PANs
  • Corrosive, irritating

  
• Photochemical smog is common in urban areas of the west US: cars + sun + mountains
• Water Vapor and Carbon Dioxide

  
  

  • This blanketing effect is known as the “greenhouse effect ”.

  • Water vapor, with its high specific heat, is a major factor in this moderating effect.

  • But increasing levels ofCO2 in the atmosphere is causing an increase in global temperatures.
• Water Vapor and Carbon Dioxide

  
  

  • Gases in the atmosphere form an insulating blanket that causes the Earth’s thermal consistency.

  • Two of the most important such gases are carbon dioxide and water vapor.