2) Vertical Structure
4) Atmospheric Issues
Lecture Objectives and Content
In this lecture we: (i) described the composition of the atmosphere, (ii) examined the
vertical structure of the atmosphere in terms of temperature, (iii) reviewed the function
of some atmospheric components, and (iv) identified environmental atmospheric issues
with a focus on pollution. These notes are not complete, your must supplement these
notes with your readings. Use these notes as a guide to focus your study.
This lecture reviews materials covered in Chapter 3 of Geosystems. Read the section
Atmospheric Composition, Temperature, and Function (2nd Edition pages 64 - 70, 3rd
Edition pages 62 - 69) and the materials under Variable Atmospheric Components (2nd
Edition pages 70 - 86, 3rd edition pages 69 - 80). In the notes below, the figure numbers
in bold refer to the 3rd edition, if the figure number in the second edition is different, it is
given in unbolded text).
The Atmosphere is the gaseous envelope that surrounds the Earth, it is a mixture of
gases and suspended liquids and solids. Aerosols are liquids and solids (but not water
or ice), that are suspended in the atmosphere.
The atmosphere is composed of a mixture of gases and suspended liquids and solids.
Some of the gaseous components have accumulated in the atmosphere as a result of
volcanic activity while oxygen has accumulated from biological processes. The
character of the atmosphere has changed from Earth’s early history. The early
atmosphere had constituents such as methane, carbon dioxide, sulphur dioxide, water
vapour, and hydrogen sulphide. The composition of the modern atmosphere is much
different. The main gases of the modern atmosphere and their concentrations are listed in
Table 3.1 (Table 3.2 in 2nd ed). These gases may be divided into Nonvariable and
Variable Gases. For the nonvariable gases (nitrogen, oxygen, argon, neon, krypton, helium) the
concentrations are relative stable over time and space. The variable gases (water vapour,
carbon dioxide, methane, CFCs, ozone) are those that can experience relatively large
changes in their concentration either over time or across space.
The concentrations of these gases is relatively stable over long periods.
• exists as primarily as N 2
• very stable gas
• enters into reactions only when abundant energy is supplied:
- by lightning,
- within an internal combustion engine (produces oxides of nitrogen: smog
- when nitrogen fixing bacteria in the soil zone produce ammonia.
• exists primarily as O 2 but also occurs as O3 (ozone) in very low concentrations
• oxygen is used for respiration by organisms, oxygen is produced by photosynthesis
• oxygen in the lower atmosphere has it origin in photosynthesis over billions of years
• it is a highly reactive gas, will form oxides with other materials (e.g. iron oxide)
The inert gases Argon, Neon, Helium, Krypton are very stable and do not enter into
chemical reactions in the atmosphere.
These gases constitute a small percentage of the total volume and mass of the
atmosphere, but they can experience spatial and temporal variations in their
Carbon Dioxide (CO 2)
• gas is essential to photosynthesis
• it is the mobile carbon in the Earth-atmospheric system
• concentrations fluctuate naturally (carbon dioxide is more soluble in cold water,
atmospheric concentrations tend to be lower during periods of continental
• in recent decades concentrations have increased from 280 ppm (~1850) to current
concentrations of 395 ppm. This increase is attributed to anthropogenic sources,
largely fossil fuel combustion. • one of the key greenhouse gases.
Water Vapour (H 2O)
• concentrations in the atmosphere are highly variable (~0.1 to 4.0 %) and are higher
in lower atmosphere
• water vapour has a short residence time in the atmosphere, it is rapidly cycled from
the oceans and land to the atmosphere
• another important greenhouse gas
Ozone (O 3)
• present in the stratosphere where it is produced from a photochemical reaction with
• stratospheric ozone is broken down by synthetic refrigerants such as CFCs
• also present near ground level where it is a component of photochemical smog
Methane (CH )
• produced from anaerobic decomposition and human industrial activities (rice
paddies, termites, cows, wetlands, natural gas production)
• occurs in low concentrations (1500 ppbv) but has experienced a doubling in the last
• an important greenhouse gas
• liquids and solids (excluding water and ice) that are temporarily suspended in the
• includes natural sources such as volcanic ash, dust, soot, sea salts, spores etc
• industrial activities also contribute particulate matter
• influence the energy balance of the Earth by increasing scatter back to space
2) Vertical Structure
From the base of the troposphere to the top of the atmosphere there is a reduction in
density (Figure 3.3a) and atmospheric pressure (Figure 3.3b). Density is mass per unit
volume, and pressure is a force applied per unit area.
Density = Mass/Volume
Pressure = Force/Area
Force = Mass*Acceleration (mg) = Weight Thus, the atmospheric pressure, at any point in the atmosphere, is si