Atmospheric Composition & Function (HL IB ESS OLD COURSE - IGNORE)
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
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
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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