C1 (Chemistry): Air Quality

This section shows links to revision materials Chemistry C1 - Air Quality.

Overview of Module

The quality of air is becoming a major world concern. In this module candidates learn about the gases that make up the Earth’s atmosphere and how its composition has changed and is still changing.

Candidates explore environmental and health consequences of certain air pollutants, and options for improving air quality in the future, such as the use of catalytic converters. The emphasis is on health issues arising from burning fuels rather than on global issues such as climate change, which is covered in Module P2: Radiation and life.

Candidates learn about the chemical relationship between the burning of fossil fuels and the production of air pollutants. This module introduces molecular elements and compounds to illustrate chemical explanations.

By analysing their own and given data on concentrations of pollutants, candidates learn about the way in which scientists use data, and also that all data have certain limitations.

Chemistry

C1 - Air quality (click on the links below for general headings or look below for more detail on what you may be tested on) 

• Chemicals in the air,
• Chemical reactions and pollutants,
• Improving air quality

C1.1 Which chemicals make up air, and which ones are pollutants? How do I make sense of data about air pollution?

1. recall that the atmosphere (air) that surrounds the Earth is made up mainly of nitrogen, oxygen  and argon, plus small amounts of water vapour, carbon dioxide and other gases

2. understand that air is a mixture of different gases consisting of small molecules with large spaces between them

3. recall that the relative proportions of the main gases in the atmosphere are approximately 78% nitrogen, 21% oxygen and 1% argon

4. understand that other gases or particulates may be released into the atmosphere by human activity or by natural processes (e.g. volcanoes), and that these can affect air quality

5. understand how the Earth’s early atmosphere was probably formed by volcanic activity and consisted mainly of carbon dioxide and water vapour

6. understand that water vapour condensed to form the oceans when the Earth cooled

7. explain how the evolution of photosynthesising organisms added oxygen to, and removed carbon dioxide from, the atmosphere

8. explain how carbon dioxide was removed from the atmosphere by dissolving in the oceans and then forming sedimentary rocks, and by the formation of fossil fuels

9. understand how human activity has changed the composition of the atmosphere by adding:

• a. small amounts of carbon monoxide, nitrogen oxides and sulfur dioxide to the atmosphere
• b. extra carbon dioxide and small particles of solids (e.g. carbon) to the atmosphere

10. understand that some of these substances, called pollutants, are directly harmful to humans (e.g. carbon monoxide reduces the amount of oxygen that blood can carry), and that some are harmful to the environment and so cause harm to humans indirectly (e.g. sulfur dioxide causes 

acid rain).

C1.2 What chemical reactions produce air pollutants? What happens to these pollutants in the atmosphere?

 

1. recall that coal is mainly carbon

2. recall that petrol, diesel fuel and fuel oil are mainly compounds of hydrogen and carbon (hydrocarbons)

3. understand that, when fuels burn, atoms of carbon and/or hydrogen from the fuel combine with atoms of oxygen from the air to produce carbon dioxide and/or water (hydrogen oxide)

4. understand that a substance chemically combining with oxygen is an example of oxidation, that loss of oxygen is an example of reduction, and that combustion reactions therefore involve oxidation

5. understand that fuels burn more rapidly in pure oxygen than in air

6. recall that oxygen can be obtained from the atmosphere and can be used to support combustion (e.g. in oxy-fuel welding torches)

7. understand that in a chemical reaction the properties of the reactants and products are different

8. understand that atoms are rearranged during a chemical reaction

9. interpret representations of the rearrangement of atoms during a chemical reaction

10. understand that 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

11. understand how sulfur dioxide is produced if the fuel that is burned contains any sulfur

12. understand how burning fossil fuels in power stations and for transport pollutes the atmosphere with:

• a. carbon dioxide and sulfur dioxide
• b. carbon monoxide and particulate carbon (from incomplete burning)
• c. nitrogen oxides (from the reaction between atmospheric nitrogen and oxygen at the high temperatures inside engines)

13. relate the formulae for carbon dioxide CO₂ , carbon monoxide CO, sulfur dioxide SO₂, nitrogen monoxide NO, nitrogen dioxide NO₂ and water H2O to visual representations of their molecules

14. recall that nitrogen monoxide 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’)

15. understand that atmospheric pollutants cannot just disappear, they have to go somewhere:

• a. particulate carbon is deposited on surfaces, making them dirty
• b. sulfur dioxide and nitrogen dioxide react with water and oxygen to produce acid rain which is harmful to the environment
• c. carbon dioxide is used by plants in photosynthesis
• d. carbon dioxide dissolves in rain water and in sea water.

C1.3 What choices can we make personally, locally, nationally or globally to improve air quality?

1. understand how atmospheric pollution caused by power stations that burn fossil fuels can be reduced by:

• a. using less electricity
• b. removing sulfur from natural gas and fuel oil
• c. removing sulfur dioxide and particulates from the flue gases emitted by coal-burning power stations

2. understand how the acid gas sulfur dioxide is removed from flue gases by wet scrubbing:

• a. using an alkaline slurry e.g. a spray of calcium oxide and water
• b. using sea water
• NOTE: Candidates are not required to write word or symbol equations

3. understand that the only way of producing less carbon dioxide is to burn less fossil fuels

4. understand how atmospheric pollution caused by exhaust emissions from motor vehicles can be reduced by:

• a. burning less fuel, for example by having more efficient engines
• b. using low sulfur fuels
• c. 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)
• d. adjusting the balance between public and private transport
• e. having legal limits to exhaust emissions (which are enforced by the use of MOT tests)

5. understand the benefits and problems of using alternatives to fossil fuels for motor vehicles, limited to biofuels and electricity.