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The greenhouse effect

The greenhouse effect is the process in which the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and the planet's surface.

Without greenhouse gasses, out planet would be covered in ice with an average temperature of 35˚C less than it is at present. The temperature of the earth is more influenced by the greenhouse effect than it is by our proximity to the Sun.

The earth receives most of it's energy in the form of electromagnetic radiation from the Sun. Incoming radiation is largely unaffected by the gases in the Earth's atmosphere: they pass straight through it.

  • Some solar energy is absorbed by the Earth's surface 
  • Some is released back into the atsmosphere
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Greenhouse gases

COis produced naturally by many natural processes:

  • volcanic eruptions
  • respiration of animals
  • burning or decay of organic matter, such as plants

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
  • Trapped in ice-like structures called clathrates. They contain 3000 times as much methane as is in the atmosphere.   
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How do gases absorb radiation

Gases can absorb radiation, causing the molecule to vibrate, Eventually, the vibrating molecule releases some of this energy in the form of radiation.

The greenhouse effect of a gas depends not only on its concentration in the atmosphere but also on its ability to absorb infrared radiation.

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Alternative fuels



  • wind turbines
  • tidal power
  • solar panels
  • nuclear plants

Each have their own drawbacks, for example wind turbines are noisy.

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Carbon capture and storage

CCS captures carbon dioxide from power stations and stores it away safely. It is considered as an immediate strategy to get rid of waste carbon dioxide.

Carbon dioxide can be store:

  • In porous rocks
  • In empty oil fields
  • In carbonates --> CaO(s)+ CO2(g) à CaCO3(s)

The UK can store a lot CO2 of because there are many old oil and gas fields which are nearing the end of their productive life. It is estimated that that the UK has other porous rocks capable of storing up to 500 years worth of COproduction.

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Ozone

Ozone is a molecule consisting of three oxygen atoms. It can be bad or good.

  • Bad: ozone near to the Earth's surface in the trophosphere is an air pollutant with harmful effects on the respiratory system of animals.
  • Good: ozone in the upper atmosphere in the stratosphere protects living organisms by preventing harmful UV from reaching the Earth's surface.  
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The ozone-oxygen cycle - UV radiation

Ozone is continuously being formed and broken down in the stratosphere by the action of UV. There are three types of UV radiation:

  • UV - a; reaches the Earth's surface. It doesn't cause much concern.
  • UV - b; can cause sunburn and genetic damage, which can result in skin cancer. 
  • UV - c; is entirely screened out by the ozone layer 

If the ozone layer were to decrease in thickness, then more UV-b could reach the Earth's surface which the result of an increase in cases of skin cancer.

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The ozone-oxygen cycle - formation of ozone

O2 + (radiation<240nm) > 2O

O2 + O > O3 + heat  

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The ozone-oxygen cycle - how the ozone layer works

O3 + (radiation<310nm) O2 + O

O2 + O > O3 + heat  

This is an equilibrium reaction.

O2 + O ßà O3 

where ßà represents an equilibrium   

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The ozone-oxygen cycle - Removal of ozone

O3 + O > 2O2

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The ozone layer - ozone depletion

The Ozone Depletion Potential (OPD) of a substance is the relative amount of breakdown to the ozone layer caused by the substance.  

The OPD for trichlorofluoromethane, CFCl3, is 1.0. Other substances are compared to it. 

Once CFCs, like trichlorofluoromethane, reach the ozone layer, they are broken into free radicals by powerful UV radiation

Draw the free radical substitution reaction for CFCl3.

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The ozone layer - regulation

Apparent benefits may be offset by unexpected and detrimental side effects. For example, CFCs have had an extremely negative impact on the ozone layer. Since this discovery was made , governments around the World have set about introducing protocol, such as the Montreal Protocol, to reduce the damage already done to the environment.

The Montreal Protocol;

  • CFCs - zero production by 2000
  • Tetrachloromethane - zero production by 2000
  • Halons - phased out by 2000
  • 1,1,1 - trichloroethane - zero by 2005
  • HCFCs and HFCs - to replace CFCs in 15% of applications
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Controlling air pollutants - the internal combusti

CO

  • A poisonous gas emitted into the atmosphere from the incomplete combustion of hydrocarbons
  • The majority of CO comes from traffic pollution
  • They can exist for about one month in the environment before being oxidised to CO2.  
  • For humans, CO can have serious health implications as CO makes oxygen compete for active sites on haemoglobin, reducing oxygen transport.
  • Symptoms for CO poisoning include reduces manual dexterity, disturbed vision, tiredness and an inability to perform complex tasks 
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Controlling air pollutants - the internal combusti

NO

  • In a combustion engine, fuel is burnt in the presence of oxygen, generating NO.
  • Nitrogen oxide and nitrogen dioxide are produced during this reaction.
  • They decrease ozone levels or are converted into nitric acid, which makes up acid rain
  • They are respiratory irritants and affect asthmatic
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Controlling air pollutants - the internal combusti

Unburnt hydrocarbons

Benzene and buta -1,3 - diene are found in unburnt fuels. They are know human carcinogens

They are broken down in the low atmosphere by sunlight. This mechanism involves radicals

Low level ozone is very serious because it can cause breathing difficulties on humid sunny days. This is particularly common in urban areas. 

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Controlling air pollutants - the internal combusti

The catalytic converter

  • All cars since 1993 have been fitted with a catalytic converter. 
  • They are usually made from platinum and supported on a honeycomb mesh.
  • In petrol engines, CO combines with NO forming non-toxic nitrogen and CO2
  • 2NO(g) + 2CO(g) à N2(g) + 2CO2(g) 



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Controlling air pollutants - the internal combusti

The catalyst provides a surface on which the reaction takes place.

  • The CO and NO diffuse over the catalytic surface. Some molecules are held to the surface by adsorption
  • Temporary bonds form between the gas molecules and the catalytic surface.
  • These bonds hold the molecules in the correct place for them to react together.
  • N2(g) + 2CO2(g) are desorbed from the surface
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CO2

Carbon dioxide has a number of uses;

  • in beer
  • as a solvent
  • decaf coffee
  • beer
  • dry cleaning
  • toxic waste treatment
  • chemical synthesis
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