C9: Chemistry of the atmosphere

Question 1

What are the approximate proportions of gases in Earth’s atmosphere today?

Answer 1

• 80%nitrogen
• 20% oxygen
• small proportions of other gases, including carbon dioxide, water vapour and noble gases.

Question 2

Theories about the Earth’s early atmosphere and how the atmosphere was formed have developed over time.

Why is evidence for the composition of the early atmosphere limited?

Answer 2

Because of the time scale of 4.6 billion years.

Question 3

Explain the theory which suggests the composition of Earth’s early atmosphere during the first billion years of its existence.

Answer 3

• intense volcanic activity released gases which formed the early atmosphere (CO₂ and nitrogen; possibly small proportions of methane and ammonia)
• volcanoes also produced water vapour that condensed to form the oceans
• the Earth’s atmosphere was like the atmospheres of Mars and Venus today, consisting of mainly carbon dioxide with little or no oxygen

Question 4

One theory suggests Earth’s early atmosphere may have consisted of mainly CO₂.

Now, there is much less CO₂ in the atmosphere; where does the theory suggest it went?

Answer 4

• When the oceans formed, carbon dioxide dissolved in the water.
• When algae and plants evolved, they decreased the percentage of CO₂ in the atmosphere by photosynthesis.
• Dissolved CO₂ went through a series of reactions to form carbonate precipitates. When marine organisms evolved, their shells and skeletons contained calcium carbonate.
• When they died, they fell to the seabed and were buried with sediment, becoming compressed over millions of years to form sedimentary rocks (limestone + coal), crude oil and natural gas.

Question 5

One theory suggests Earth’s early atmosphere may have consisted of mainly CO₂ and little or no oxygen gas.

Now, the atmosphere is approximately 20% oxygen; how does the theory suggest it appeared?

Answer 5

• Algae first produced oxygen, about 2.7 billion years ago, by photosynthesis:

carbon dioxide + water → glucose + oxygen

• Soon after this, oxygen appeared in the atmosphere.
• Over the next billion years, plants evolved.
• The percentage of oxygen gradually increased to a level that enabled animals to evolve.

Question 6

Explain how deposits of limestone, coal, crude oil and natural gas formed.

Answer 6

• When the oceans formed, carbon dioxide dissolved in the water.
• Dissolved CO₂ went through a series of reactions to form carbonate precipitates. When marine organisms evolved, their shells and skeletons contained calcium carbonate.
• When they died, they fell to the seabed and were buried with sediment, becoming compressed over millions of years to form sedimentary rocks (limestone + coal), crude oil and natural gas.

Question 7

What are greenhouse gases?

Answer 7

Gases which act as an insulating layer in Earth’s atmosphere, allowing Earth to be warm enough to support life.

Question 8

Name 3 greenhouse gases.

Answer 8

• water vapour
• carbon dioxide
• methane

Question 9

Explain the greenhouse effect.

Answer 9

• short-wavelength radiation from the Sun hits the Earth’s surface and is reradiated back out as long-wavelength radiation
• greenhouse gases in the atmosphere (including CO₂ and methane) absorb much of this and reradiate it in all directions, including back towards Earth
• this long-wavelength radiation is thermal radiation, so results in the heating of the Earth’s surface

Question 10

Explain how the greenhouse effect is related to global heating.

Answer 10

• greenhouse gases in the atmosphere absorb long-wavelength radiation that has been reradiated from the Earth’s surface, and reradiate it in all directions, including towards the earth - this is the greenhouse effect.
• the heat retained by the Earth should be in equilibrium with the heat it emits (so that the planet is at a constant temperature)
• but increasing levels of greenhouse gases have disrupted the balance, meaning earth is heating up - this is global heating.

Question 11

Name 2 human activities which increase the amount of methane in the atmosphere.

Answer 11

• agriculture: farm animals produce methane through digestive processes
• decomposition of waste (including agricultural) produces methane (as well as CO₂)

Question 12

Name 3 human activities which increase the amount of carbon dioxide in the atmosphere.

Answer 12

• deforestation
• burning fossil fuels
• creation of waste - its decomposition releases CO₂ (as well as methane)

Question 13

In what ways does deforestation increase the amount of carbon dioxide in the atmosphere?

Answer 13

• Removing vegetation means less CO₂ is removed from the atmosphere
• The combustion and decay of vegetation also releases CO₂
• Deforestation is done either to create space for crops (agricultural waste releases CO₂ and methane) or for farm animals (which release methane)

Question 14

Based on peer-reviewed evidence, many scientists believe that human activities cause the heating of the Earth’s surface, and that this results in global climate change.

Why is there misrepresentation and “skepticism”?

Answer 14

It is difficult to model global climate change, as it’s such a complex system.

This leads to simplified models, speculation, and potentially biased opinions presented in the media that may be based on only parts of the evidence.

Question 15

An increase in average global temperature is a major cause of climate change. Describe 5 potential effects of global climate change.

Answer 15

• sea level rise (caused by expansion of water and polar ice caps melting), leading to coastal erosion, increased flooding and loss of habitats.
• changes in rainfall patterns. Along with increased temperatures, this may affect the ability of some regions to produce food.
• increased frequency and severity of storms
• reduction in biodiversity (heating leads to changes in habitats)
• changes in animal migration patterns and distribution of species (due to rainfall and temperature changes)

Question 16

Define “carbon footprint”.

Answer 16

The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.

Question 17

Why is carbon footprint difficult to measure?

Answer 17

There are many different factors to consider - manufacturing, use, disposal - since carbon footprint is measured over something’s full life cycle.

Question 18

Describe 5 actions (8 total) that can be taken to reduce carbon dioxide and methane emissions.

Answer 18

• using renewable or nuclear energy, rather than fossil fuels
• using more efficient processes to cut emissions and reduce waste
• using a technology that captures CO₂ emitted by fossil fuel combustion, then storing it underground
• governments could tax individuals/corporations based on emissions
• governments could cap emissions and sell licences beyond that point
• individuals can walk/cycle/use public transport rather than drive
• individuals can reduce how often they use air travel
• individuals can save energy at home, e.g. turn down heating

Question 19

Why may governments not want to place taxes or caps to limit greenhouse gas emissions?

Answer 19

• Doing this could impact on economic growth, which could affect people’s wellbeing, especially in developing countries.
• It’s hard for international agreements to be made (and stuck to) as many governments are apprehensive to sacrifice their economic development if they think others won’t do the same.

Question 20

There exists technology which has the potential to reduce greenhouse gas emissions. Why is it limited?

Answer 20

• many technologies, such as carbon capture and storage, are still in developmental stages
• many renewable energy technologies are still expensive in comparison to unsustainable sources

Question 21

Why is cutting greenhouse gas emissions on the individual scale limited?

Answer 21

• some people don’t want to make sacrifices to their lifestyle
• there may not be enough education provided about why and how to make changes

Question 22

What is released into the atmosphere when fossil fuels are combusted completely?

Answer 22

• fossil fuels contain hydrocarbons
• during combustion, the hydrogen and carbon in these compounds are oxidised
• so carbon dioxide and water vapour are released into the atmosphere

Question 23

What is released into the atmosphere when fossil fuels are combusted incompletely?

Answer 23

• fossil fuels contain hydrocarbons
• incomplete combustion is where there is not enough oxygen for all of the fuel to burn
• when fossil fuels combust incompletely, particulates (small, solid particles, including soot (carbon) and unburned hydrocarbons) are released
• carbon monoxide is also released as well as carbon dioxide

Question 24

How is sulfur dioxide produced by burning fuels?

Answer 24

• fossil fuels such as coal contain sulphur impurities
• when they are burned, the sulfur becomes oxidised and is released into the atmosphere

Question 25

How are nitrogen oxides produced by burning fuels?

Answer 25

• the heat from combustion (e.g. in car engines) causes the air to become very hot
• this heat triggers nitrogen in the air to oxidise

Question 26

How is carbon monoxide dangerous?

Answer 26

• carbon monoxide is toxic, but odorless and colourless, so not easily detected
• it binds to haemoglobin in your blood (which is supposed to carry oxygen), meaning less oxygen is transported around the body
• a lack of oxygen to cells leads to fainting, comas and potentially death

Question 27

How are sulfur dioxide and oxides of nitrogen harmful?

Answer 27

• they cause respiratory problems in humans
• when they dissolve in water in clouds, acid rain falls
• acid rain kills plants, damages infrastructure and corrodes metal

Question 28

How are particulates harmful?

Answer 28

• when inhaled, they cause damage in the lungs, leading to respiratory problems
• particulates reflect sunlight back into space, causing global dimming