UNIT 4 LESSON 9 – CHEMISTRY OF THE ATMOSPHERE
The Proportions of Different Gasses in the Atmosphere
For 200 million years, the proportions of different gasses in the atmosphere have been much the same as they are today:
~4/5 (80%) nitrogen
~1/5 (20%) oxygen
Small proportions of various other gasses, i.e. CO2, H2O (g) and noble gasses.
The symbol “∼” means around/approximately.
The Earth’s Early Atmosphere
Evidence is limited because of the time scale of 4.6 billion years and theories have changed and developed over time.
One theory suggests that during the first billion years of the Earth’s existence;
There was intense volcanic activity that released gasses that formed the early atmosphere.
At the start of this period, the atmosphere may have been like the atmospheres of Mars and Venus today: mainly CO2 with little or no O2 (g).
Volcanoes also produced nitrogen (N2) which gradually built up in the atmosphere & there may have been small proportions of methane (CH4) and ammonia (NH3).
Water vapor condensed to form the oceans.
CO2 dissolved in the water and carbonates were precipitated producing sediments, and reducing the amount of CO2 in the atmosphere.
This theory is the only theory of the early atmosphere you need to know.
How Oxygen Increased
Algae & plants produce the O2 that is now in the atmosphere by photosynthesis.
6CO2 + 6H2O → C6H12O6 + 6O2
carbon dioxide + water –(light) → glucose + oxygen
Algae first produced oxygen about 2.7 billion years ago and soon after this oxygen appeared in the atmosphere.
Over the next billion years, plants evolved and the % oxygen gradually increased to a level that enabled animals to evolve.
How Carbon Dioxide Decreased
Algae and plants decreased the % CO2 in the atmosphere by photosynthesis.
CO2 was also decreased by the formation of sedimentary rocks that contain carbon (e.g. limestone and coal) and by the production of fossil fuels from the remains of dead plants and animals when they decayed.
Greenhouse Gasses
Maintain temperatures on Earth high enough to support life.
Include: water vapor, CO2 & CH4
The greenhouse gas effect:
Electromagnetic radiation at most wavelengths (both long and short) from the sun passes through the Earth’s atmosphere.
The Earth absorbs some radiation and thus warms up (essential for life on Earth). But some heat is radiated from the Earth as infrared radiation.
Some of this IR radiation is absorbed by greenhouse gasses in the atmosphere.
The atmosphere warms up leading to the greenhouse effect and global warming.
Human Activities Which Contribute to an Increase in Greenhouse Gases in the Atmosphere
Activities increase levels of CO2 & CH4
Examples of human activities that contributes in the increase of greenhouse gasses include:
Driving (CO2)
Consuming electricity (CO2)
Raising livestock (cows – CH4)
Decay of organic waste in landfill sites (CH4)
Based on peer-reviewed evidence, many scientists believe that human activities will cause the temperature of the Earth’s atmosphere to increase at the surface and that this will result in global climate change.
But, it is difficult to model such complex systems as global climate change.
This leads to simplified models, speculation and opinions presented in the media that may be based on only parts of the evidence and which may be biased.
Global Climate Change
An increase in average global temperature is a major cause of climate change.
There are several potential effects of global climate change, including:
Extinction of species
Rising sea levels due to the melting of polar ice caps
Migration → people will move from areas suffering drought/flooding
Decrease in crop yield for all major world crops
The Carbon Footprint and Its Reduction
Carbon footprint - the total amount of CO2 and other greenhouse gasses emitted over the full life cycle of a product, service, or event.
It can be reduced by reducing emissions of carbon dioxide and methane e.g. by using less electricity (so using less fossil fuels or using an alternative source of electricity), by reducing the amount of travel or transportation (of either goods or people), and by planting more trees.
However, action may be limited because it’s more difficult, can be more expensive, and planting trees takes away land that could be used to grow crops.
Atmospheric Pollutants from Fuels
Combustion of fuels is a major source of atmospheric pollutants.
Most fuels (including coal) contain carbon and/or hydrogen and may also contain some sulfur.
The gasses released into the atmosphere when a fuel burns may include carbon dioxide, water (vapor), carbon monoxide, and oxides of nitrogen (which are formed at high temperatures). Solid particles and unburned hydrocarbons may also be released, forming particulates in the atmosphere.
If there’s not enough oxygen, some of the fuel doesn’t burn – this is partial/incomplete combustion. Here, solid particles of soot (carbon), carbon monoxide, and unburnt fuel are released.
The combustion of hydrocarbons releases energy. During combustion, the carbon and hydrogen in the fuels are oxidized to form carbon dioxide and water .
Properties and Effects of Atmospheric Pollutants
Carbon monoxide: toxic gas that is colorless and odorless so not easy to detect.
Sulfur dioxide and oxides of nitrogen: cause acid rain and respiratory problems in humans.
Particulates: cause global dimming and human health problems.
The Proportions of Different Gasses in the Atmosphere
For 200 million years, the proportions of different gasses in the atmosphere have been much the same as they are today:
~4/5 (80%) nitrogen
~1/5 (20%) oxygen
Small proportions of various other gasses, i.e. CO2, H2O (g) and noble gasses.
The symbol “∼” means around/approximately.
The Earth’s Early Atmosphere
Evidence is limited because of the time scale of 4.6 billion years and theories have changed and developed over time.
One theory suggests that during the first billion years of the Earth’s existence;
There was intense volcanic activity that released gasses that formed the early atmosphere.
At the start of this period, the atmosphere may have been like the atmospheres of Mars and Venus today: mainly CO2 with little or no O2 (g).
Volcanoes also produced nitrogen (N2) which gradually built up in the atmosphere & there may have been small proportions of methane (CH4) and ammonia (NH3).
Water vapor condensed to form the oceans.
CO2 dissolved in the water and carbonates were precipitated producing sediments, and reducing the amount of CO2 in the atmosphere.
This theory is the only theory of the early atmosphere you need to know.
How Oxygen Increased
Algae & plants produce the O2 that is now in the atmosphere by photosynthesis.
6CO2 + 6H2O → C6H12O6 + 6O2
carbon dioxide + water –(light) → glucose + oxygen
Algae first produced oxygen about 2.7 billion years ago and soon after this oxygen appeared in the atmosphere.
Over the next billion years, plants evolved and the % oxygen gradually increased to a level that enabled animals to evolve.
How Carbon Dioxide Decreased
Algae and plants decreased the % CO2 in the atmosphere by photosynthesis.
CO2 was also decreased by the formation of sedimentary rocks that contain carbon (e.g. limestone and coal) and by the production of fossil fuels from the remains of dead plants and animals when they decayed.
Greenhouse Gasses
Maintain temperatures on Earth high enough to support life.
Include: water vapor, CO2 & CH4
The greenhouse gas effect:
Electromagnetic radiation at most wavelengths (both long and short) from the sun passes through the Earth’s atmosphere.
The Earth absorbs some radiation and thus warms up (essential for life on Earth). But some heat is radiated from the Earth as infrared radiation.
Some of this IR radiation is absorbed by greenhouse gasses in the atmosphere.
The atmosphere warms up leading to the greenhouse effect and global warming.
Human Activities Which Contribute to an Increase in Greenhouse Gases in the Atmosphere
Activities increase levels of CO2 & CH4
Examples of human activities that contributes in the increase of greenhouse gasses include:
Driving (CO2)
Consuming electricity (CO2)
Raising livestock (cows – CH4)
Decay of organic waste in landfill sites (CH4)
Based on peer-reviewed evidence, many scientists believe that human activities will cause the temperature of the Earth’s atmosphere to increase at the surface and that this will result in global climate change.
But, it is difficult to model such complex systems as global climate change.
This leads to simplified models, speculation and opinions presented in the media that may be based on only parts of the evidence and which may be biased.
Global Climate Change
An increase in average global temperature is a major cause of climate change.
There are several potential effects of global climate change, including:
Extinction of species
Rising sea levels due to the melting of polar ice caps
Migration → people will move from areas suffering drought/flooding
Decrease in crop yield for all major world crops
The Carbon Footprint and Its Reduction
Carbon footprint - the total amount of CO2 and other greenhouse gasses emitted over the full life cycle of a product, service, or event.
It can be reduced by reducing emissions of carbon dioxide and methane e.g. by using less electricity (so using less fossil fuels or using an alternative source of electricity), by reducing the amount of travel or transportation (of either goods or people), and by planting more trees.
However, action may be limited because it’s more difficult, can be more expensive, and planting trees takes away land that could be used to grow crops.
Atmospheric Pollutants from Fuels
Combustion of fuels is a major source of atmospheric pollutants.
Most fuels (including coal) contain carbon and/or hydrogen and may also contain some sulfur.
The gasses released into the atmosphere when a fuel burns may include carbon dioxide, water (vapor), carbon monoxide, and oxides of nitrogen (which are formed at high temperatures). Solid particles and unburned hydrocarbons may also be released, forming particulates in the atmosphere.
If there’s not enough oxygen, some of the fuel doesn’t burn – this is partial/incomplete combustion. Here, solid particles of soot (carbon), carbon monoxide, and unburnt fuel are released.
The combustion of hydrocarbons releases energy. During combustion, the carbon and hydrogen in the fuels are oxidized to form carbon dioxide and water .
Properties and Effects of Atmospheric Pollutants
Carbon monoxide: toxic gas that is colorless and odorless so not easy to detect.
Sulfur dioxide and oxides of nitrogen: cause acid rain and respiratory problems in humans.
Particulates: cause global dimming and human health problems.
