Chemistry of the atmosphere

Question 1

What is the atmosphere?

Answer 1

The layer of gases surrounding the Earth which is held in place by gravity

Question 2

Which gases make up the atmosphere?

Answer 2

• 78.09% (4/5) nitrogen
• 20.95% (1/5) oxygen
• <1% carbon dioxide, water vapour and noble gases (e.g. argon)

Question 3

How was the early atmosphere formed?

Answer 3

In the first billion years, the Earth was really dry due to intense volcanic activity which released loads of carbon dioxide, water vapour and nitrogen, alongside small amounts of methane and ammonia into the atmosphere.

Question 4

How did the atmosphere change with the formation of the oceans?

Answer 4

• Around a billion years later, the Earth began to cool which allowed the water vapour in the atmosphere to condense into liquid water, forming the oceans
• Lots of carbon dioxide in the atmosphere dissolved in the oceans, forming carbon precipitates that later became sediment on the seabed

Question 5

What is the disadvantage of theories about Earth’s early atmosphere?

Answer 5

• Evidence is limited due to the time scale of 4.6 billion years

Question 6

How did atmospheric carbon dioxide levels decrease?

Answer 6

• Around 2.7 billion years ago, algae and green plants started to photosynthesise over billions of years, which lowered carbon dioxide levels whilst building up oxygen levels
• This change in atmosphere allowed for more complex life to evolve

Question 7

What happened when the photosynthetic organisms died?

Answer 7

• They fell to the seabed and were buried in layers of sediment for billions of years
• This sediment compressed to form sedimentary rock and fossil fuels which trapped the carbon to stop it from getting back into the atmosphere
• Crude oil and natural gas were formed mainly from dead plankton
• Coal was formed from thick deposits of dead plant material
• Limestone was formed mainly from the calcium carbonate in the shells and skeletons of marine organisms

Question 8

What is the difference between weather and climate?

Answer 8

• Weather refers to short-term atmospheric conditions (e.g. sunny, rainy, windy)
• Climate describes the long-term weather conditions in a specific region (e.g. temperature, precipitation, wind)

Question 9

How does the greenhouse effect work?

Answer 9

• Short wavelength solar radiation from the sun passes through the atmosphere and hits the Earth
• Some of this energy is absorbed by the surface, but most is either re-emitted or reflected back towards space as long wavelength infrared radiation
• Only some of the energy reaches space, the rest of it is absorbed by greenhouse gases (e.g. carbon dioxide, methane, water vapour)
• These gases re-emit the energy, and this process of absorption and emission repeats over and over again
• This trapped energy maintains the temperatures high enough to support life

Question 10

Which human activities increase the amount of carbon dioxide in the atmosphere?

Answer 10

• Burning lots of fossil fuels releases the carbon that was trapped inside the fuel as carbon dioxide
• Deforestation means that there is less photosynthesis so the carbon dioxide is not being removed from the atmosphere

Question 11

Which human activities increase the amount of methane in the atmosphere?

Answer 11

• Increased demand for meat and dairy products means that there is an increased farming of animals who release lots of methane during digestion
• Methane is released when the huge amounts of landfill waste are decomposed by microorganisms

Question 12

What is the difference between global warming and climate change?

Answer 12

• Global warming refers to the overall increase in the Earth’s temperature, mainly due to the enhanced greenhouse effect; this is a cause of climate change
• Climate change refers to the large-scale effects on the climate (e.g. shifts in temperature, precipitation, wind); this is a consequence of global warming

Question 13

What are the consequences of global climate change?

Answer 13

• Extreme weather events (e.g. droughts, hurricanes, floods) will become more common and severe
• Sea levels rise due to the melting of ice caps and due to the fact that water expands when it is heated; this leads to seasonal flooding, and the submersion of islands and coastal towns
• Species perfectly adapted to their environment may become extinct as they will not be able to adapt to their new conditions or migrate fast enough
• Therefore, biodiversity is likely to fall dramatically

Question 14

What is a carbon footprint?

Answer 14

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

This estimate allows us to identify the most polluting activities so that we can reduce their emissions

Question 15

Why is it difficult to calculate a carbon footprint?

Answer 15

We have to take in account many things such as:
- How the raw materials are sourced
- The manufacturing process
- Total amount of fuel it will use over its lifetime
- Transporting the parts
- How it is disposed of

Question 16

How can we reduce our carbon footprints?

Answer 16

• Use renewable energy resources (e.g. wind, solar, nuclear) instead of fossil fuels
• Use more efficient manufacturing processes that use less energy and produce less waste
• Governments can introduce new laws and regulations, or tax companies based on the amount of greenhouse gases they emit
• Recycle products rather than disposing them into a landfill
• Carbon capture technology traps carbon and stores it deep underground

Question 17

Why is it difficult to reduce our carbon footprints?

Answer 17

• Renewable energy is often more expensive than fossil fuels
• Many of our existing products (e.g. cars) require fossil fuels which makes it really hard to switch
• Governments worry that the economy will suffer if they prioritise the environment which makes international agreements very difficult

Question 18

What is the word equation of incomplete combustion?

Answer 18

hydrocarbon + oxygen —> (carbon +) carbon monoxide + water

Question 19

When does incomplete combustion occur?

Answer 19

When hydrocarbons are burned in a limited supply of oxygen

Question 20

Why is incomplete combustion problematic?

Answer 20

• Carbon particulates (soot) damage our lungs and cause respiratory problems
• Soot also forms clouds of smog which reflect sunlight back to space; this contributes to global dimming
• Carbon monoxide is a toxic, colourless and odourless gas. It diffuses into our bloodstream and binds with haemoglobin permanently. Cells cannot get enough oxygen for respiration which causes symptoms such as fainting, coma or death

Question 21

How are nitrogen oxides and sulfur dioxide formed?

Answer 21

• Sulfur is an impurity in some fossil fuels so when we burn them, the sulfur is oxidised to form sulfur dioxide gas
• Nitrogen oxides are formed when nitrogen and oxygen from the air react together
• This doesn’t normally happen because it requires really high temperatures
• However, these temperatures are reached inside internal combustion engines like those of cars

Question 22

Why are nitrogen oxides and sulfur dioxide harmful?

Answer 22

• These pollutants damage our lungs and cause respiratory problems
• When these gases combine with water vapour, they dissolve to form dilute sulfuric acid or dilute nitric acid which then fall as acid rain
• Acid rain damages buildings and statues
• Acid rain also corrodes metals
• It also damages plants by making the soil more acidic