Chemistry of the Air

Question 1

How is infrared radiation absorbed in our atmosphere?

Answer 1

It is absorbed by the C=O, O-H and C-H bonds in water, carbon dioxide and methane. These absorptions contribute to global warming

Question 2

Greenhouse Effect of a gas

Answer 2

Determined by its atmospheric concentration and its ability to absorb infrared radiation

Question 3

How can chemists help control global warming?

Answer 3

• Providing evidence to governments to show global warming is happening and is an issue
• Investigating solutions to environmental problems
• Monitoring progress of governments reducing carbon emissions

Question 4

Solutions to greenhouse effect

Answer 4

• Using alternative fuels (e.g. wind power, nuclear etc)

- Carbon capture and storage

Question 5

CCS

Answer 5

Carbon capture and storage

• removal of waste carbon dioxide as a liquid injected deep in the oceans
• storage in deep geological formations/in old oil and gas fields: helps extracting last little bit of oil
• reacting with metal oxides to form stable carbonate minerals

Question 6

Kyoto protocol

Answer 6

An agreement that committed countries to reducing their carbon emissions by 5% by 2012. Unfortunately, the biggest emitters of carbon, the USA didn’t sign :(

Question 7

Ozone-oxygen cycle

Answer 7

Ozone is continuously broken down and reformed in the stratosphere by the action of ultraviolet radiation
O(3) + (radiation of < 310nm) -> O(2) + O
O(2) + O -> O(3) + heat
This way, harmful radiation is converted to heat, without losing ozone
O(2) + O O(3) : an equilibrium is reached

Question 8

Formation of ozone in the stratosphere

Answer 8

O(2) + (radiation < 240nm) -> 2O

O(2) + O -> O(3) + heat

Question 9

Why is ozone important

Answer 9

The constant formation and breaking down of the ozone layer converts UV radiation into heat. UV-c is completely absorbed by the ozone layer; 95% of UV-b is absorbed: UV-b causes sun burn and skin cancer - don’t want too much of this! Only 5% of UV-a is absorbed, but it is much less damaging! The ozone layer protects us from harmful effects of high-energy UV radiation

Question 10

Catalysing the breakdown of the ozone layer

Answer 10

R + O(3) -> RO + O(2)
RO + O -> R + O2
Overall: O(3) + O -> 2O(2)
As R is reproduced, it is essentially a catalyst
R could be Cl’ from CFCs or ‘NO from nitrogen oxides (from lighting and aircraft engines)

Question 11

How are CO, NO(x) and unburnt hydrocarbons formed in an internal combustion engine

Answer 11

• CO: incomplete combustion of hydrocarbons in the engine due to lack of oxygen
• NO(x): air is drawn into the cylinder along with the fuel. As the fuel is burnt in the presence of oxygen, and temperatures are very high NO(x) is produced as nitrogen is oxidised.
• Unburnt hydrocarbons: Volatile organic compounds are released from unburnt fuels

Question 12

Why are CO. NO(x) and unburnt hydrocarbons bad?

Answer 12

• CO: binds strongly to haemoglobin in blood, reducing its ability to carry oxygen. High levels can cause death from oxygen starvation
• NO(x): formation of low level ozone (see below). Also forms nitric acid when combines with water in atmosphere contributing to acid rain. NO(x) are respiratory irritants
• Unburnt hydrocarbons: react with nitrogen dioxide in the presence of sunlight, forming low level ozone. This causes breathing difficulties and increases susceptibility to infections

Question 13

How the catalyst in a catalytic converter functions

Answer 13

-CO and NO molecules diffuse over the catalytic surface of the metal. Some are held on by adsorption
-Temporary bonds form between the catalytic surface and the gas molecules
-The bonds hold the molecules in position as this reaction occurs:
2NO(g) + 2CO(g) -> N(2)(g) + 2CO(2)(g)
-The CO(2) and N(2) gases are then desorbed from the surface and diffuse away

Question 14

Monitoring air pollution

Answer 14

Infrared spectroscopy can be used to monitor air pollution. As certain frequencies of infrared will be absorbed by certain molecules as they contain certain bonds, the spectrum that is seen can be used to identify the presence of greenhouse gases and the levels they are found in in the atmosphere

Question 15

Why do we need to control global warming?

Answer 15

Due to global warming:

• Rivers overflow (melting glaciers and rainfall) and drought
• Longer growing seasons in some regions but drought and disease in others
• More extreme storms and hurricanes
• Sea ice is melting faster, potentially shutting off Gulf Stream, leading to severe winters in northern Europe and UK
• Water in oceans expands, so sea levels are rising, potentially flooding populated land