Atmospheric Composition & Function (DP IB Environmental Systems & Societies (ESS))

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

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

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

• 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