OCR 21st century C1

Atmosphere and AIr
1. The 15km thick atmosphere that surrounds the Earth is made up of 78% nitrogen, 21% oxygen and 1% argon
2. Air is made up of small molecules with large spaces inbetween them. Molecules are groups of atoms joined together
  1. Other gases such as sulfur dioxide, carbon monoxide/dioxide, nitrogen dioxide, water vapour or particulates may be released into the atmosphere by human activity such as burninf fossil fuels in power stations and for transport or by natural processes (e.g. volcanoes).
    1. Sulfur dioxide is formed when fuels containing sulfur compounds are burned. Sulfur dioxide reacts with water and oxygen in the air to produce acid rain. This removes sulfur dioxide from the air, but the acid rain corrodes buildings and kills plants.
    2. Nitrogen monoxide reacts in the atmosphere to form nitrogen dioxide.
      2. NO is formed during the combustion of fuels in air, and is subsequently oxidised to nitrogen dioxide NO2 (NO and NO2 are jointly referred to as ‘NOx’)
    3. Nitrogen dioxide also reacts with water and oxygen in the air to produce acid rain. Can cause breathing problems
      1. (from the reaction between atmospheric nitrogen and oxygen at the high temperatures inside engines)
    4. Carbon monoxide is produced when fuel is burned in an insufficient supply of oxygen. It is a poisonous gas that reduces the amount of oxygen the blood can carry
      1. Incomplete combustion
    5. Carbon dioxide dissolves in rain water and sea water. It is used by plants in photosynthesis. Excess levels of CO2 can give rise to global warming
    6. Deposited on surfaces, making them dirty. Can be breathed into the lungsand can worsen asthma and lung infections
4. Early Atmosphere
  1. Earth’s early atmosphere was probably formed by volcanic activity and consisted mainly of carbon dioxide and water vapour
    1. Water vapour condensed to form the oceans when the Earth cooled
      1. The evolution of photosynthesising organisms added oxygen to, and removed carbon dioxide from, the atmosphere
        carbon dioxide was removed from the atmosphere by dissolving in the oceans and then forming sedimentary rocks, and by the formation of fossil fuels
        human activity has small amounts of carbon monoxide, nitrogen oxides and sulfur dioxide to the atmosphere
        human activity has added extra carbon dioxide and small particles of solids (e.g. carbon) to the atmosphere
Production of Pollutants
1. Coal is mostly carbon and impurities
  2. combines with oxygen from the air to produce carbon dioxide
    1. These combustion reactions involve oxidation
2. petrol, diesel fuel and fuel oil are mainly compounds of hydrogen and carbon
  1. Hydrogen from the fuel combines with atoms of oxygen from the air to produce hydrogen oxide (water).
3. Fuels burn more rapidly in pure oxygen which can be obtained from the atmosphere
  1. can be used to support combustion (e.g. in oxy-fuel welding torches)
Reactions
1. during the course of a chemical reaction the numbers of atoms of each element must be the same in the products as in the reactants, thus conserving mass
2. understand that in a chemical reaction the properties of the reactants and products are different.
  1. understand that atoms are rearranged during a chemical reaction interpret representations of the rearrangement of atoms during a chemical reaction
Reducing Pollution
1. pollution caused by power stations that burn fossil fuels
  1. removing sulfur dioxide and particulates from the flue gases emitted by coal-burning power stations
    1. using sea water
      1. naturally alkaline
    2. Using an alkaline slurry e.g. a spray of calcium oxide and water
      1. When mixed with air and sprayed with the lurry, the sulfur dioxide in flue gases reacts and forms solid calcium sulphate. this solid is removed allowing clean gas to escape
        Waste gases from the furnace, containing particulates are passed into the electrostatic precipitator
        The particulates pass though a negatively cahrged metal grid and lose electrons picking up a negative charge
        They attract to the positive plate
        The particulates are removed and waste gases pass through
  2. removing sulfur from natural gas and fuel oil
  3. using less electricity
2. to produce less carbon dioxide, less fossil fuels need to be burnt
3. Vehicular pollution
  1. burning less fuel, for example by having more efficient engines
  2. using low sulfur fuels
  3. using catalytic converters (in which nitrogen monoxide is reduced to nitrogen by loss of oxygen, and carbon monoxide is oxidised to carbon dioxide by gain of oxygen)
  4. adjusting the balance between public and private transport
    1. having legal limits to exhaust emissions (which are enforced by the use of MOT tests)
4. Alternatives
  1. Biofuels
    1. Renewable source made from plant matter
      1. The growing of these crops requires CO2 which is released back into the atmosphere when the fuels burn.
        Crops are grown for fuel instead of food
        2-3% of fuel can be mixed into fuel without changing engines
5. Electric vehicles
  1. Don't produce waste gases
    1. Electricity comes from fossil fuel burning power stations
      1. Need regular and long recharging
Air Quality

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OCR 21st century C1

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	Created by Pritesh Patel about 8 years ago