Atmospheric Composition & Function (HL IB ESS OLD COURSE - IGNORE)

Revision Note

Atmospheric Composition & Function

  • The atmosphere forms the boundary between Earth and space

  • It is the outer limit of the biosphere

  • The atmosphere supports life on Earth

Atmospheric gases and their redistribution

  • The atmosphere is mainly composed of nitrogen (about 78%) and oxygen (about 21%)

    • These two gases make up the majority of the atmosphere and play vital roles in supporting life on Earth

  • The atmosphere contains smaller amounts of other gases, including:

    • Carbon dioxide

    • Argon

    • Water vapour

    • Various trace gases

  • Carbon dioxide, although present in relatively low concentrations (around 0.04%), is essential for:

    • Photosynthesis in plants

    • Maintaining the greenhouse effect

  • Argon is an inert gas that does not participate in chemical reactions but contributes to the overall composition of the atmosphere

  • Water vapour plays an important role in:

    • Photosynthesis in plants

    • The Earth's weather patterns

    • The formation of clouds and precipitation

  • Trace gases, such as methane, ozone, and nitrous oxide, are present in even smaller quantities

    • However, they still have significant impacts on climate and atmospheric chemistry

Pie chart showing Earth's atmosphere composition: 78% nitrogen, 21% oxygen, 0.96% other gases (mostly argon), and 0.04% carbon dioxide.
The gaseous composition of the Earth's atmosphere

Redistribution through physical processes

  • Gases in the atmosphere are moved around by various physical processes, including:

    • Wind: the main mover of gases, caused by differences in air pressure

    • Convection: warm air rises and cool air sinks, creating vertical movement

    • Diffusion: gases spread from areas of high concentration to areas of low concentration

    • Turbulence: irregular air flow caused by obstacles like mountains and buildings

    • Jet streams: fast-flowing, narrow air currents in the upper atmosphere

Atmospheric layers

  • Atmospheric stratification:

    • The atmosphere is divided into layers based on temperature changes

    • The key layers for living systems are the troposphere and the stratosphere

  • Troposphere:

    • The lowest layer, extending up to about 10 km from the Earth's surface

    • Weather phenomena, such as clouds, precipitation, and gas mixing, occur here

    • Contains the highest concentration of water vapour, carbon dioxide and other important trace gases

  • Stratosphere:

    • Located above the troposphere, extending from about 10 to 50 km above the Earth's surface

    • Contains the ozone layer, which absorbs and blocks most of the Sun's harmful ultraviolet (UV) radiation

  • Importance of inner layers:

    • Various reactions in the troposphere and stratosphere are vital for maintaining the balance of gases, regulating climate and supporting life

    • In the troposphere, chemical reactions involving pollutants, greenhouse gases and particles impact air quality and climate

    • In the stratosphere, chemical reactions involving ozone maintain the ozone layer and protect organisms on Earth from harmful UV radiation

Graph of Earth's atmospheric layers showing altitude, pressure, and temperature. Layers: Troposphere, Stratosphere (with ozone), Mesosphere, Thermosphere.
Approximate atmospheric temperatures and pressures up to an altitude of about 120 km—note the warmer temperatures in the troposphere, below the zone of maximum ozone concentration (in the stratosphere)

Differential heating and the tricellular model

  • Differential heating of the atmosphere:

    • The Sun heats the Earth and its atmosphere unevenly

    • The equator receives more direct sunlight, making it warmer

    • The poles receive less direct sunlight, making them cooler

    • This results in an effect known as the tricellular model of atmospheric circulation

      • This model explains how heat is distributed from the equator to the poles

Atmospheric Systems

  • The atmosphere is a highly dynamic system

    • It plays a crucial role in the Earth's climate and weather patterns

    • As with other systems, the atmospheric system is made up of storages, flows, inputs and outputs

  • Storages:

    • The atmosphere acts as a storage for gases

    • These gases are present in different concentrations

    • These concentrations can vary over time due to natural and human activities

    • This includes greenhouse gases like carbon dioxide and methane

      • These gases contribute to the greenhouse effect and influence the Earth's temperature

  • Flows:

    • Within the atmosphere, there are constant flows of gases and particles

    • These flows are driven by processes such as air currents, weather patterns and atmospheric circulation

    • These flows contribute to the movement and redistribution of gases and other substances within the atmosphere

  • Inputs:

    • The atmosphere receives inputs from various sources

    • Natural inputs include:

      • Gases emitted from volcanic eruptions

      • Gases emitted from plants and other living organisms

      • Dust particles from desert regions

    • Anthropogenic inputs, resulting from human activities, include:

      • Greenhouse gases (e.g. from fossil fuel combustion and livestock)

      • Air pollutants from industrial processes

      • Aerosols from combustion

Industrial facility at sunset with smoke billowing from a tall smokestack, silhouetted against a cloudy sky, and four additional smokestacks in the background.
Human activities such as emissions from industrial chimneys create inputs into atmospheric systems (Photo by Michal Pech on Unsplash)
  • Outputs:

    • Gases maybe be removed from atmospheric systems through natural processes like respiration and photosynthesis

    • Pollutants and aerosols can be removed from the atmosphere through, e.g. precipitation and dry deposition

  • Exchanges and interactions with other Earth systems:

    • The atmosphere interacts with other components of the Earth system

      • This includes the biosphere (plants, animals, and microorganisms), hydrosphere (oceans, lakes, and rivers), and lithosphere (landmasses and rocks)

    • It exchanges gases and particles with these systems through various mechanisms

      • E.g. the exchange of carbon dioxide occurs through photosynthesis by plants and respiration by organisms

    • These interactions involve the exchange of gases, energy and particles

      • This shapes climate patterns, weather events and overall Earth system dynamics

Examiner Tips and Tricks

You need to be familiar with the tricellular model of atmospheric circulation, as this is an important part of Topic 2.4 (Climate & Biomes).

You should recall how this model explains the behaviour of atmospheric systems and the distribution of precipitation and temperature at different latitudes.

It also explains how these factors influence the structure and relative productivity of different terrestrial biomes.

Go back and have a look at this revision note again if you need to revise it!

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