Global Warming

Global Warming

the greenhouse effect
1. earth recieves most of its energy in the form of electromagnetic radiation from the sun. Mostly from the visible reigion of the spectrum, with small amounts from the infrared and ultraviolet regions
  1. The incoming radiation is realtively unaffected by the gases in the Earth's atmosphere, and passes straight through to the Earth's surface.
    1. Most infrared radiation emitted by the earth's surfaces goes back into space. However, certain gases in the atmosphere absorb some of this IR. It is then re-emitted as energy, with some passing back towards the Earth. This process effectively traps much of the heat in the lower atmosphere.
      1. In CO2, a linear molecule, the c-o bond absorbs IR causing the molecule to vibrate. Eventually the vibrating molecule emits some of this energy in the form of radiation. This can then be absorbed by another greenhouse gas molecule or at the Earth's surface. In H2O, the O-H bonds absorb IR, in methane, the C-H bonds absorb IR.
        The greenhouse effect of a gas depends not only on its concentration in the atmosphere, but also on its ability to absorb IR.
        The absorbtion-emission process keeps the heat close to the earth's surface.
2. natural process, keeping our planet at a temperature capable of supporting human life.
  1. Human activity is producing more greenhouse gases, which threaten to upset this fine natural balance, resulting in global warming.
3. creates an equilibrium. The earth's surface and atmospheric gases absorb energy at the same rate as it radiates energy, thus maintaining a steady temperature.
4. greenhouse gases
  1. occur naturally in the atmosphere. Water Vapour is the most abundant of them, with CO2 the next. CO2 is produced by; volcanic erruptions, respiration of animals. burning or decay of organic matter, such as plants. The third most abundant is methane, although present in smaller quantities than CO2, methane makes a greater contribution to the greenhouse effect than the same amount of CO2. Methane is: emitted during the production of coal, natural gas and oil; a product of rotting organic waste in landfill sites; released from certain animals, especially cows, as a by-product of digestion; also found in large quantities trapped in ice like structures under the cold northen seas (clathrates).
5. global warming potential
  1. related to the lifetime of a gas in the atmosphere, as well as the ability of the gas to absorb IR.
    1. some chloroflourocarbons (CFCs) are much more efficient at absorbing IR than CO2 but, since legislation banned the large-scale use of CFCs, their effect is diminishing.
  2. luckily the atmospheric concentrations of CFCs and other molecules with a high GWP have always been much lower than for CO2 and H2O
Climate Change
1. Solutions
  1. Alternative fuels
    1. wind turbines
    2. tidal power
    3. solar panels
    4. nuclear plants
  2. Carbon Capture and Storage
    1. captures CO2 from power stations and stores it away safely, instead of it being released into the atmosphere. It is an immediate strategy to get rid of waste CO2 gas.
    2. underground porous rocks can act as a sponge to store CO2 gas and keep it from leaking away
    3. old oil and gas fields are great natural containers for CO2 gas
    4. decarbonised fuels
      1. reduce carbon emissions by about 90%
      2. CH4 + 2H2O = CO2 + 4H2
        the remaining CO2 will then be seperated and piped offshore to an oilfield which is nearing the end of its productive life
        the hydrogen could be burnt as a truly clean fuel, and the CO2 could be captured and stored safely
      3. could be fitted into existing power stations and petrochemical plants.
    5. the UK alone can store an extortionate amount of CO2
    6. storage as carbonates (Mineral storage)
      1. CO2 is reacted with metal oxides to produce stable carbonates (carbonate rocks)
        CaO + CO2 = CaCO3 MgO + CO2 = MgCO3
      2. occurs naturally, for example limestone rocks. natural reaction is very slow and efforts to increase the rate are very energy intensive. More research is required if mineral storage is to become a viable form of CCS
ozone
1. the ozone layer
  1. good ozone
    1. in the stratosphere; protects living organisms by preventing harmful UV light from reaching the Earth's surface
  2. bad ozone
    1. in the troposphere; air pollutant wuth harmful effects on the respiratory system of animals.
  3. found in the stratosphere, filters out the shorter UV wavelengths (less than 320 nm). These shorter wavelengths would be very damaging to life.
    1. the ozone converts this UV radiation into heat and consequently, the ozone layer is at a higher temp than other parts of the upper atmosphere.
  4. the ozone-oxygen cycle
    1. ozone is continuously being formed and broken down in the stratosphere by the action of UV radiation which occurs in three types.
      1. UV-a (320-400nm)
        reaches the earth's surface, only 5% absorbed by ozone. less energy than shorter wavelengths and not as damaging, doesn't cause much concern.
      2. UV-b (280-320nm)
        95% absorbed, can cause sunburn and sometimes genetic damage, which can result in skin cancer, if exposure is prolonged
        although ozone screens out most of UV-b, some does reach the Earth's surface. Any decrease in the ozone layer would allow more UV-b to reach the surface and increase the genetic damage to living organisms.
      3. UV-c (200-280nm)
        100% absorbed, entirely screened out by the ozone layer.
    2. O2 + (radiation < 240nm) = 2O
      1. O2 + O = O3 + heat
        O3 + (radiation < 310nm) = O2 + O
        O2 + O = O3 + heat
        removal of ozone O3 + O = 2O2
        luckily for us, the removal rate is slow, since the concentration of O atoms is very low
2. Ozone depletion
  1. it is recognized that most chlorine radicals in the stratosphere are generated by human activity. This has upset the natural ozone-oxygen balance, leading to problems in maintaining the protective ozone layer. Chlorine radicals mainly come from CFCs which can take years to reach the reach the ozone layer.
    1. initiation: CFCl3 (UV) = Cl. + CFCl2.
      1. propogation: Cl. + O3 = ClO. + O2 ClO. + O = Cl. + O2
        overall: O3 + O = 2O2
    2. nitrogen oxide radicals from lightning and aircraft engines also destroy the ozone.
      1. propagation: NO. + O3 = NO2. + O2 NO2. + O = NO. + O2
        overall: O3 + O = 2O2
air pollution
1. internal combustion engine
  1. Carbon Monoxide
    1. poisonous gas, emitted due to incomplete combustion of hydrocarbons/organic compounds, mainly occurs from traffic pollution, mainly from urban areas. Exists from 1 month before is oxidised into CO2. serious health implications on humans.
  2. Oxides of Nitrogen
    1. air is drawn into the engine cylinder, some of the N from the air is oxidised by the oxygen under this high temp process. NO and NO2 are produced, the concentrations of which are higher in urban areas where traffic levels are high. NO2 forms low level ozone, and nitric acid, a contributor to acid rain, nitrogen oxides are respiratory irritants and effect asthmatics even in low levels.
  3. Unburnt Hydrocarbons
    1. volatile organic compounds are released, usually from unburnt fuels. Two compounds of particular concern are benzene and buta-1,3-diene, both of which are found in petrol in small quantities and are know human carcinogens. Once released into the atmosphere, the unburnt HC and NO2 react together to form low-level ozone, the energy of this reaction is provided by sunlight. the mechanism involves radicals. low-level ozone is a serious pollutant, causing breathing difficulties and increasing susceptibility to infections. Urban areas are more prone to low level ozone formation.
2. Infrared spec is currently being developed to monitor environmental pollution.
3. The catalytic converter
  1. oxidation catalyst
    1. used on diesel engines to to decrease emissions of CO and unburnt hydrocarbons. Combined with complex filter systems, they also remove particulate matter and nitrogen oxides.
      1. 2CO + O2 = 2CO2
        C12H26 + 18.5O2 = 12CO2 + 13H2O
  2. three-way catalyst
    1. fitted to petrol engines. In this system, NO reacts with CO to form the non-toxic gases N and CO2
      1. 2NO + 2CO = N2 + 2CO2
    2. provides a surface on which the reaction takes place.
      1. CO and NO molecules diffuse over the catalytic surface of the metal. Some of the molecules are held on to the metal surface by adsorption.
        Temporary bonds are formed between the catalytic surface and the gas molecules.
        These bonds hold the gas molecules in the right position on the metal surface, where they react together.
        After the reaction, the N2 and CO2 products are desorbed from the surface and diffuse away from the catalytic surface.
Green Chemistry
1. using renewable resources: plant based substances or solar energy instead of using finite resources such as fossil fuels, that will eventually run out.
2. companies will save money from not having to treat hazardous waste, or by using fewer chemicals or less energy.
3. preventing any waste in the first place, so that time and money is not spent on cleaning up later.
4. maximize atom economy.
5. Recycling and biodegradability: At the end of their use, materials should either be recycled, or easily broken down in the environment into harmless substances.

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