Unit 2.4 Resources Flashcards
Why can the incoming radiation from the sun pass straight through the Earth’s atmosphere?
It is relatively unaffected by the gases in the Earth’s atmosphere
Where does Earth receive most of its energy from?
The Sun, in the form of electromagnetic radiation
Once the radiation has passed through to the Earth’s surface, what happens to it?
- Most is absorbed by the Earth’s surface, warming it
- Some is released back into the atmosphere as longer-wave infrared radiation
What happens to the infrared radiation that is emitted by the Earth’s surface?
Most goes back into space
But certain gases in the atmosphere absorb some of this infrared radiation:
- It is then re-emitted as energy
- Some passes back towards the Earth
- This traps much of the heat in the lower atmosphere
What is the greenhouse effect?
The process in which the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and the planet’s surface
Why does the greenhouse effect maintain a steady temperature?
It creates an equilibrium:
- The Earth’s surface and atmospheric gases absorbs energy at the same rate as it radiates energy
What are the 3 most abundant greenhouse gases?
Water vapour
Carbon dioxide
Methane
Where does the water vapour in the atmosphere come from?
From evaporation of lakes and oceans
Where does the carbon dioxide in the atmosphere come from?
Volcanic eruptions
Respiration of animals
Burning or decay of organic matter, such as plants
Where does the methane in the atmosphere come from?
Emitted during the production of coal, natural gas and oil
A product of rotting organic waste in landfill sites
Released from certain animals as a by-product of digestion
How do gases absorb radiation?
- Certain bonds absorb infrared radiation (such as O-H, or C-H)
- This causes the molecule to vibrate
- Eventually, the vibrating molecule emits of this energy in the form of radiation
- This can then be absorbed by another greenhouse gas molecule or at the Earth’s surface
What does the greenhouse effect of a gas depend on?
- Its concentration in the atmosphere
- Its ability to absorb infrared radiation
What effects is global warming having?
- Rivers overflow due to excessively heavy rainfall and melting glaciers. In other areas, drought-like conditions lead to water shortages
- In some regions, longer growing seasons improve crop yields, whereas others experience drought and disease resulting in disastrous harvests
- Storms and hurricanes are becoming more extreme
- Sea ice in the Arctic is melting faster each year. There are fears that the Gulf Stream current may be shut off, leading to severe winters in Northern Europe
- Increasing temps expand the water in the oceans. Together with extra water from melting land ice, sea levels are rising.
Why is carbon capture and storage (CCS) useful?
It is an immediate strategy to get rid of waste carbon dioxide gas
How does CCS do?
- It captures carbon dioxide from power stations and stores it away safely, instead of it being released into the atmosphere.
- The Earth has many safe, stable areas in which we can store gases that we don’t want
How does CCS work?
A decarbonised fuel will be produced by reforming natural gas into a mixture of H2 and CO2:
CH4 + 2H2O ———> CO2 + 4H2
The CO2 will then be separated and piped offshore to an oilfield which is nearing the end of its productive life.
How else could carbon be stored?
In stable minerals:
- CO2 would be trapped by converting it into a carbonate rock
- It is reacted with metal oxides to produce stable carbonates
What is the troposphere?
The lowest layer of the Earth’s atmosphere, extending from the Earth’s surface up to about 7km (above the poles) and to about 20km (above the tropics)
How is ozone bad for the environment?
Ozone near to the Earth’s surface in the troposphere is an air pollutant with harmful effects on the respiratory systems of animals
How is ozone good for the environment?
Ozone in the upper atmosphere in the stratosphere protects living organisms by preventing harmful ultraviolet light from reaching the Earth’s surface
What is the stratosphere?
The second layer of the Earth’s atmosphere, containing the ‘ozone layer’, about 10km to 50km above the Earth’s surface
Where is the ozone layer found?
In the stratosphere, about 10-50km above the Earth’s surface
What does the ozone layer filter out?
- Ultraviolet radiation from the Sun has wavelengths in the range 270-400nm
- The ozone layer filters out the shorter wavelengths (less than 320nm)
Why is the ozone layer at a higher temperature than other parts of the upper atmosphere?
- It converts the shorter wavelengths of UV radiation into heat
- This heat is released into the ozone layer, warming it
What are the 3 different types of UV radiation?
- UV-a (320-400nm)
- UV-b (280-320nm)
- UV-c (200-280nm)
What is the effect of UV-a radiation?
- Reaches the Earth’s surface
- It has less energy than the shorter wavelengths and is not as damaging
- Doesn’t cause us too much concern
What is the effect if UV-b radiation?
Although ozone screens out most UV-b, some does reach the Earth’s surface:
- Can cause sunburn
- Can sometimes cause genetic damage
- This can result in skin cancer, if exposure to UV-b is prolonged
What effect does UV-c have?
None - it is entirely screened out by the ozone layer
How is ozone formed?
- O2 molecules absorb UV radiation with a wavelength of less than 240nm (high-energy radiation)
- This breaks the O2 molecule into 2 oxygen atoms
- The O atoms then react with O2 molecules to form ozone molecules, O3
- This process generates heat
- The heat is absorbed by air molecules in the stratosphere, raising the temperature
How does the ozone layer work?
- The ozone molecules formed absorb UV with wavelengths between 240 and 310 nm
- This converts O3 molecules back to O2 molecules and O atoms
- Chemically, this is the reverse of the reaction that forms ozone
- The atomic oxygen, O, produced immediately reacts with other O2 molecules to reform ozone
- And so the cycle continues
- In this way, the chemical energy released when O and O2 combine is converted into heat energy
- The overall effect is to convert penetrating UV radiation into heat, without any net loss of ozone
- This cycle keeps the ozone layer in a stable balance
- A natural steady rate is reached in which ozone is being formed at the same rate as it is being broken down
- It is this process that protects living organisms from the harmful effects of high-energy UV radiation
How is ozone removed?
When an oxygen atom and an ozone molecule combine, they form 2 O2 molecules
Why is the removal rate of ozone slow?
- The concentration of O atoms is very low
- But human activity can affect this balance
What is the Ozone Depletion Potential (ODP) of a substance?
The relative amount of breakdown to the ozone layer caused by the substance
What effect can the introduction of new compounds into the environment have?
It can lead to ozone loss and disruption of the natural equilibrium
Where have most of the chlorine radicals in the stratosphere come from?
- They are generated by human activity
- They have mainly come from chlorofluorocarbons, CFCs
How are CFCs broken down?
- They are very stable
- So they can only be broken down by the extremely energetic UV radiation found above most of the ozone layer
- Initiation step: a C-Cl bond is broken when UV radiation strikes a CFC molecule, producing a chlorine radical, Cl•
- Propagation step 1: the chlorine radical is extremely reactive, so it can react with an O3 molecule, breaking it apart and destroying the ozone, producing ClO• and O2
- Propagation step 2: The ClO• then reacts with an oxygen atom, to produce another chlorine radical and O2
- This chlorine radical is free to attack another ozone molecule
- So the 2 propagation steps repeat in a cycle many thousands of times
What atmospheric pollutants does the internal combustion engine in a modern car emit?
- Carbon monoxide
- Oxides of nitrogen
- Unburnt hydrocarbons
Why is carbon monoxide pollution bad for humans?
- Carbon monoxide can bind strongly to haemoglobin in the blood, reducing the amount of oxygen supplied to tissues and organs
- The heart and brain are severely affected
How is carbon monoxide released into the atmosphere?
From the incomplete combustion of hydrocarbons and other organic compounds
How are oxides of nitrogen produced in the internal combustion engine?
- During the burning of fuels, air is drawn intro the cylinder along with the fuel
- The fuel is burned in the presence of oxygen, generating energy
- Nitrogen oxides are also produced during this high-temperature process, because some of the nitrogen from the air is oxidised by the oxygen
- 2 oxides of nitrogen are produced: nitrogen monoxide and nitrogen dioxide
What effect does nitrogen dioxide have on the environment?
- It can be converted into nitric acid, a contributor to acid rain
- It can react with unburnt hydrocarbons to form low-level ozone
- The mechanism leading to ozone formation involves radicals
- Low-level ozone is a serious pollutant, causing breathing difficulties and increasing susceptibility to infections
What provides the energy for the reaction of unburnt hydrocarbons and nitrogen dioxide to produce low-level ozone?
Sunlight
Why does the concentration of low-level ozone build up on humid sunny days?
The still air contains large quantities of hydrocarbons and oxides of nitrogen
What is the catalytic converter made from?
- It is made from platinum, rhodium and palladium
- It is supported on a honeycomb mesh
- The honeycomb arrangement provides a large surface area
How does the catalytic converter work?
- Hot exhaust gases pass over the catalytic surface and the harmful gases are converted into less harmful products
- These are then released into the atmosphere
What are the 2 different types of catalytic converters?
Oxidation catalyst
3-way catalyst
Why is an oxidation catalyst used?
- It is used on diesel engines
- Decreases emissions of carbon monoxide and unburnt hydrocarbons
- It can also remove particulate matter and nitrogen oxides, when combined with complex filter systems
