C9 - Chemistry of the Atmosphere

For how long have the proportions of different gases in the atmosphere been much the same as they are today?

200 million years

What gases are in the atmosphere today?

1. 4/5ths nitrogen (78%)
2. 1/5th oxygen (21%)
3. small proportions of other gases including CO2, water vapour and noble gases like argon

Why is evidence for the early atmosphere limited?

Because of the time scale of 4.6 billion years

Describe one theory for the development of the atmosphere.

1. Intense volcanic activity - first billion years, produced gases including nitrogen which gradually built up.
2. Oceans - water vapour condensed to form oceans as the Earth cooled.
3. Atmosphere - mainly carbon dioxide, some nitrogen, a little methane and ammonia, no oxygen. Like Mars and Venus.
4. CO2 was reduced as it was dissolved in water and carbonates were precipitated producing sediments.

How did oxygen levels increase?

1. Algae and plants first produced oxygen through photosynthesis 2.7bn years ago.
2. Over the next billion years plants evolved and the percentage of oxygen increased until animals were able to evolve.

Photosynthesis equation

6CO2 + 6H2O -> C6H12O6 + 6O2 (water + carbon dioxide -> glucose + oxygen)

How did carbon dioxide levels decrease?

1. Algae and plants decreased the percentage by photosynthesis
2. Formation of sedimentary rocks and fossil fuels that contain carbon

How were deposits of coal formed?

Plants died and formed a layer of plant deposits which compressed in the absence of oxygen to form coal (a sedimentary rock)

How were deposits of limestone formed? (2)

1. Carbon is transferred to animal tissues including their skeletons and shells.
2. These built up at the bottom of the ocean. The pressure caused by being buried caused the deposits to form limestone.

How was crude oil and natural gas formed? (2)

1. Plankton were deposited in muds on the sea floor
2. They were covered and compressed by sediments that became layers of rock over millions of years to form crude oil and natural gas

'Locked up' carbon

Carbon which is trapped within the Earth's crust in rocks and fossil fuels

What do greenhouse gases in the atmosphere do?

Maintain temperature on Earth high enough to support life

Name 3 greenhouse gases

Water vapour, carbon dioxide and methane

Describe the greenhouse effect in terms of the interaction of short and long wavelength radiation with matter.

1. The Earth is heated by short wavelength radiation from the Sun (UV and visible light)
2. Some energy is reflected back into space.
3. Short wavelength radiation passes through the atmosphere as it does not interact very much with the gas molecules in the atmosphere
4. The energy is absorbed by the Earth
5. The Earth emits longer wavelength infrared radiation
6. This long wavelength radiation is absorbed by greenhouse gases and causes a temperature increase

What effect do some human activities have on the amounts of greenhouse gases in the atmosphere?

Increases it

What gases does this include?

Carbon dioxide and methane

Describe 2 human activities that increase carbon dioxide levels in the atmosphere

1. Burning fossil fuels e.g. coal for electricity, diesel to power cars, gas to heat homes
2. Deforestation - trees in rainforests which would normally absorb CO2 are being burned to provide land for cattle (burning also increases CO2)

Describe 2 human activities that increase methane levels in the atmosphere

1. Agriculture - flooded rice paddy fields; these grow in anaerobic conditions and produce methane
2. Cows - release methane when they pass wind, number of grazing cattle increase to provide food

Based on ... many scientists believe that...

Based on peer-reviewed evidence many scientists believe that human activities will cause the temperature of the Earth's atmosphere to increase at the surface and that this will result in global climate change.

What is our difficulty in understanding climate change and what does this lead to?

1. It is difficult to model such complex systems as climate change.
2. Leads to simplified models, speculation and opinions presented in the media that may be based only on parts of evidence and which may be biased

False claims of evidence

Claims based on poor evidence or bias

Uncertainties surrounding climate change

We cannot predict with certainty how much the temperature of the atmosphere will increase

A minority of scientists argue that...

...the rises observed are due to the natural variations that have always happened throughout the long history of earth

Scientists must work harder to...

...communicate the ideas of climate change to the general public

Describe a source of evidence for climate change

Ice cores which have gases trapped inside - these gases can be analysed to see how the atmosphere has change over time

What is a major cause of climate change?

An increase in average global temperatures

Describe 4 potential effects of climate change

1. Rising sea levels - due to melting ice caps and expansion of warmer oceans, could flood low-lying areas
2. Increasingly common extreme weather events - e.g. more frequent and severe storms
3. Changing distribution of rainfall - affects food-producing capacity of different regions
4. Changing distribution of wildlife - some species extinct, change in distribution of insect-borne diseases like malaria

Carbon footprint

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

How can the carbon footprint be reduced?

By reducing emissions of carbon dioxide and methane

Describe actions taken by governments to reduce carbon footprint

1. Carbon capture - deposit CO2 in an underground geological formation where it can be absorbed into porous rocks
2. Taxes - polluter pays a tax so there is an incentive to reduce CO2
3. Carbon offset - increase carbon sink through reforestation
4. Support the use of biofuels
5. Support renewable sources - e.g. wind and solar energy

Describe actions we can personally take to reduce our carbon footprint

1. Energy efficient homes - cavity wall insulation, low energy light bulbs, appliances switched off, double glazed windows, solar panels
2. Use cars less - take public transport which uses less CO2 per person
3. Higher efficiency cars - electric cars
4. Plant-based diets - less demand for beef so less cows producing methane

Describe problems with reducing the carbon footprint

1. Expensive - people reluctant to pay
2. Inconvenient - e.g. walking instead of driving
3. Scientific disagreements
4. People need information about climate change so that everyone can make a positive contribution

What is a major source of atmospheric pollutants?

The combustion of fuels

What do most fuels including coal contain?

Carbon and/or hydrogen, and may also contain some sulfur

What gases may be released into the atmosphere when a fuel is burned?

Carbon dioxide, water vapour, carbon monoxide, sulfur dioxide, and oxides of nitrogen

What may also be released into the atmosphere and what happens to them?

Solid particles and unburned hydrocarbons may be released that form particulates

Formation and effects of carbon monoxide

1. Formed during incomplete combustion (limited supply of oxygen)
2. A toxic gas which is not easily detected as it is colourless and odourless; bonds with haemoglobin and prevents red blood cells carrying oxygen

Formation and effects of soot (carbon particles)

1. Incomplete combustion
2. Cause global dimming as they travel into the atmosphere and reflect sunlight back into space. Also cause health problems in humans such as damaging lungs

Formation and effects of sulfur dioxide

1. Burning fossil fuels - reacts with oxygen
2. Dissolves in water to form sulfuric acid & acid rain which damages trees and kills animal and plant life in lakes, as well as attacking buildings. Also causes respiratory problems

Formation and effects of nitrogen oxides

1. Nitrogen and oxygen react at high temperatures (e.g.in car engines)
2. Nitrogen oxides dissolve in water to form acid rain as with sulfur dioxide. Also cause respiratory problems.

Formation and effects of carbon dioxide

1. Complete combustion of fossil fuels
2. Enhances greenhouse effect