Chemistry of the atmosphere

Evolution of the atmosphere

  • In the first billion years, the earth was very dry and had intense volcanic activity

    • This created lots of carbon dioxide, water vapour and nitrogen and smaller amounts of methane and ammonia

  • The early atmosphere was mainly carbon dioixde

  • Water vapour then condensed to form oceans, in which lots of carbon dissolved

    • This formed carbon precipitates and eventually sediments

  • 2.7 billion years ago algae began to appear slowly, and then evolved to create lots of green plants rapidly

    • These plants could photosynthesise - CO2 + H2O → C6H12O6 + O2

      • CO2 levels decreased as it was taken in

      • O2 levels increased as it was released (levels built up)

      • From this oxygen, more complex life forms evolved - animals

  • Plants can only hold small amounts of carbon in their bodies

    • When they died, they settled in the seabed and became buried by layers of sediment

    • Over millions of years, it compressed to form sedimentary rock, oil and gas with trapped carbon

      • This prevented the release of carbon into the atmosphere

    • The substance that was formed from dead matter depends on what organism was buried originally

      • Crude oil and gas - mainly from dead plankton

      • Coal - a sedimentary rock, mainly from dead plant material

      • Limestone - a sedimentary rock, from calcium carbonate (in shells and skeletons)

Greenhouse gases and climate change

  • Around the earth, there is a trapped layer of gases that form the atmosphere

    • These gases act as an insulating layer (a greenhouse)

      • It traps the perfect amount of the sun’s thermal energy so earth is a warm and stable temperature

  • Short wave length radiation is emitted from the sun, part of which is absorbed into the earth, but most is re-emitted/reflected back to space

    • This energy is re-emitted as long wave length radiation, some of which makes it back to space but most is absorbed by particles of gas in our atmosphere

    • After a short delay, energy is re-emitted again from the particles, either towards space or the earth

      • Most of this energy is absorbed by gas particles, and then re-emitted - this cycle repeats

      • This means the heat energy remains close to earth - maintains a warm and stable temperature

  • Carbon dioxide, methane and water vapour are all greenhouse gases

    • The warming they cause is called the greenhouse effect

  • Because humans are producing lots of these gases, their concentration is increasing

    • Increases the greenhouse effect, which leads to global warming

  • Carbon dioxide increase is caused by:

    • Deforestation - less photosynthesis to remove CO2

    • Burning fossil fuels - releases stored carbon

  • Methane increase is caused by:

    • Farm animal’s digestion

    • Huge amounts of waste - releases methane as it decomposes

  • There are lots of variables that add to global warming, so its difficult to predict what will happen

    • The impact it causes is called climate change

  • Climate change is the effect of global warming on long term weather patterns

    • Rare weather events are becoming more common and severe

      • Droughts, floods, hurricanes

    • Sea levels are rising due to ice melting into oceans

      • Water temperature is increasing which causes seasonal flooding and potential submersion of places

    • General effect on biodiversity as species might not adapt to new conditions fast enough

      • Some species may adapt or migrate, but its not common

Carbon footprints

  • A carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over something’s entire lifecycle

    • A product, service or event

  • The benefits to calculating carbon footprints are:

    • Can calculate if something is something is worth the cost of how environmentally damaging it is

    • Can identify the most polluting activities

  • The issues with calculating carbon footprints are:

    • It is hard to measure carbon footprint accurately

      • Have to take materials used and where they were sourced, the manufacturing process and it’s end disposal, as well as transport, etc.

    • It is only a rough estimate, but we can get an idea on what is best/worst

  • Reducing greenhouse gas emissions

    • Using renewable energy sources

    • More efficient manufacturing processes

      • Less energy use

      • Less waste (can decompose and release methane)

    • Governments

      • Can make new laws

      • Can tax companies for greenhouse gas emission

    • Carbon capture technology

      • Captures carbon dioxide from burning fossil fuels and it stores it underground

  • Currently, renewable energy is more expensive and everything is built on fossil fuels (cars, machinery, etc.)

  • Governments worry if they prioritise the environment that the economy may suffer and international agreements become difficult

Air pollution

  • Burning fossil fuels produce carbon dioxide and water, as well as releasing lots of energy

    • This only happens when pure hydrocarbons are burnt with plenty of oxygen - allows for complete combustion

    • This doesn’t always happen, and instead pollutants are produced (carbon monoxide, soot, sulphur dioxide, nitrogen oxides)

  • Hydrocarbon + excess oxygen → water = carbon dioxide

    • Complete combustion

  • When three isn’t enough oxygen present, incomplete combustion occurs

    • Carbon monoxide and particulates (solid carbon particles - soot) are formed

  • Particulate issues

    • If inhaled, it can damage lungs and cause respiratory problems

    • It can form dark clouds (smog), so sunlight is reflected back to space - less light on earth

      • This is called global dimming

  • Carbon monoxide issues

    • It is very dangerous

    • If it is breathed in, it diffuses into the blood stream and binds to haemoglobin

      • This means less oxygen can be carried, so less is transported around the body

      • It can lead to fainting, comas and death

    • It is colourless and odourless, so hard to detect

  • Some hydrocarbons that are burnt have impurities

    • For example, sulphur which gets oxidised when burnt to form sulphur dioxide (SO2)

  • When the oxygen formed reacts with nitrogen in the air, nitrogen oxide is formed

    • Only happens at very high temperatures, so unusual

    • Can happen in internal combustion engines (cars)

  • When sulphur dioxide and nitrate oxides are formed, they cause lots of issues

    • When breathed in, they can damage lungs and cause respiratory problems

    • As the gases mix with cloud, they dissolve to form dilute sulphuric acid or dilute nitric acid

      • This falls as acid rain

  • Acid rain issues

    • It corrodes metals

    • Damages buildings and statues

    • Damages plants - either direct contact or through soil becoming acidic (difficult to grow)

    • If in water (oceans, rivers), fish can ingest it and become ill

DONE!!!