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Greenhouse Gases and the Greenhouse Effect

Key Concepts

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Greenhouse Gases

Sources of greenhouse gases, the length of time they exist in the atmosphere, and the percentage of emissions they represent are shown in the table below:

Gas Name
(Symbol)
Common Sources Sinks Atmospheric
Lifetime
(years)
%
Emissions
carbon dioxide

(CO2)

(i) combustion of fossil fuels
(ii) deforestation
(iii) gas flaring
(iv) cement production
(i) photosynthesis
(ii) ocean surface
5 to 200 60

methane

(CH4)

(i) landfills
(ii) production and distribution of natural gas and petroleum
(iii) fermentation from digestive system of livestock
(iv) rice cultivation
(v) natural wetlands
(vi) combustion of fossil fuels
(i) reaction with tropospheric hydroxyl (OH)
(ii) removal by soils
12 20

nitrous oxide

(N2O)

(i) combustion of fossil fuels
(ii) fertilizers
(iii) manure
(iv) nylon production
(v) biological sources in oceans and soils
(i) removal by soils
(ii) stratospheric photolysis
114 6

hydrofluorocarbons

(HFCs)

(i) aerosol propellants
(ii) refrigeration gases
(iii) foam-blowing agents
(iv) solvents
(v) fire retardants
(vi) aluminium smelting
(vii) semiconductor production
(i) CFCs, HCFCs removal by stratospheric photolysis
(ii) HCFC, HFC reaction with tropospheric hydroxyl (OH)
2 to 50,000 (dependent on compound) < 14%

perfluorocarbons

(PFCs)

(i) aluminium production
(ii) semiconductor production
  > 10,000 < 1%

sulfur hexafluoride

(SF6)

(i) electrical transmission and distribution systems
(ii) circuit breakers
(iii) magnesium production
  3,200 < 1%

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The Greenhouse Gas Effect

Greenhouse gases in the earth's atmosphere absorb infrared radiation from the ground.

This radiation (heat) is re-emitted in all directions. Heat radiated back towards the earth's surface leads to the warming of the surface.

Using data from ice cores and other sources, scientists have been able to determine the temperature variation and carbon dioxide concentrations on earth over time:

Since 1950, temperature variations have been observed that can not be explained solely on the basis of the presence of natural greenhouse gases.

Scientists have modeled this unusual temperature variation to take into account man-made sources of greenhouse gases and have found that this may explain the temperature variations being observed.

During the 21st century, the earth is likely to experience:

Suggestions for combatting global warming have been:

Finding alternatives to these greenhouse gases in chemical and industrial processes has led to the development of a new branch of chemistry called Green Chemistry.

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