Download - Environmental Chemistry
Environmental Chemistry
greenhouse effect,
global warming,
Greenhouse effect
Describe the greenhouse effect. List the main greenhouse gases and their
sources, and discuss their relative effects. Discuss the influence of increasing
amounts of greenhouse gases on the atmosphere.
Greenhouse effectGreenhouse effect
Natural greenhouse effect: absorption of infrared radiation by natural greenhouse gases (CO2 and H2O vapour) in the atmosphere warming the earth – if not surface would be 30K cooler.
Anthropogenic greenhouse effect: caused by gases emitted by human activities.
solar radiation spectrumsolar radiation spectrum
Greenhouse Analogy: Energy from the sun in the form of some ultraviolet and visible light (short wavelength) passes through the glass of the greenhouse. As the light strikes various surfaces in the greenhouse they are heated. These surfaces in turn re-radiate the heat in the form of infrared radiation (long wavelength). However, the IR radiation is blocked from escaping by the glass. IR is not able to pass through the glass, hence the greenhouse air heats up fairly dramatically.
natural greenhouse effectnatural greenhouse effecthttp://www.elmhurst.edu/~chm/vchembook/globalwarmA5.htmlhttp://www.elmhurst.edu/~chm/vchembook/globalwarmA5.html
The greenhouse gases have the same property as the glass towards the IR radiation. Think of the greenhouse gases acting as an invisible glass shield around the earth.
terminologyterminology greenhouse effectgreenhouse effect = the absorbing of some
of the infra-red radiation radiated from the Earth in the atmosphere which is then reradiated back to Earth; this results in…
global warmingglobal warming = a gradual increase in planet-wide temperatures
Global warming:Global warming: evidence global temperatures since 1850shttp://www.ncdc.noaa.gov/oa/climate/research/anomalies/anomalies.html
What can the mean global temperature anomaly be used for? This product is a global-scale climate diagnostic tool and provides a big picture overview of average global temperatures compared to a reference value.
Global warming:Global warming: evidence http://en.wikipedia.org/wiki/Image:Instrumental_Temperature_Record.png
Global warming:Global warming: http//pubs.acs.org/cen/news/83/i48/8348notw1.html
Thin slice of ice – gas bubbles are dark
Ice core from 2874 m depth, 491 000 years old
Global warming: COGlobal warming: CO22 emissions emissionshttp://www.eia.doe.gov/oiaf/1605/ggccebro/chapter1.htmlhttp://www.eia.doe.gov/oiaf/1605/ggccebro/chapter1.html
Global warming: Global warming: methane emissionsmethane emissions
Global warmingGlobal warmingTrends in greenhouse gas emissionsTrends in greenhouse gas emissions
Greenhouse gasesGreenhouse gaseshttp://www.elmhurst.edu/~chm/vchembook/globalwarmA5.htmlhttp://www.elmhurst.edu/~chm/vchembook/globalwarmA5.html
seasonal fluctuations of carbon dioxide
seasonal fluctuations of carbon dioxide
The cyclic change is caused by the seasonal variation of the growth of vegetation from the Northern Hemisphere. Starting in May the growth of plants and trees uses carbon dioxide, so the concentration decreases a little bit. Starting in October, November the growth ceases, thus causing the carbon dioxide to increase.
(from http://www.elmhurst.edu/~chm/vchembook/globalwarmA3.html)
Greenhouse gasesGreenhouse gaseshttp://www.atmosphere.mpg.de/enid/253.htmlhttp://www.atmosphere.mpg.de/enid/253.html
Water vapour absorbs most wavelengths of the infra-red radiation emitted by the Earth's surface, trapping it as heat. At some wavelengths, however, the absorption is weak or close to zero allowing infra-red radiation to escape into space. Other greenhouse gases absorb infra-red radiation at these wavelengths and reduce the amount of heat lost into space.
Atmospheric windowhttp://en.wikipedia.org/wiki/Atmospheric_window
Global warming effects (1)
World wide rise in sea levels resulting from: Partial melting of glaciers and polar ice caps Thermal expansion of water (as a result of
heating).
Changes in crop yields: some crops will grow better, other worse.
Global warming effects (2)
Changes in distribution of commercial crops Changes in the distribution of pests and disease-
carrying organisms e.g. malaria. More severe weather conditions:
floods in particular of coastal areas; more severe storms e.g. monsoon floods in Pakistan 2010
More severe droughts e.g. 2010 worst drought in Amazon
greenhouse gases definitionGreenhouse gases are gases that: allow visible light and UV radiation (short-
wavelength/high frequency) to pass through them but (because of the nature of their covalent bonds
in their molecules) absorb the infrared radiation (longer-wavelength radiation) of the same frequency as the one the Earth converts the energy from the Sun into and
reradiates this infrared radiation back to the Earth.
greenhouse effect their ability to absorb heat or infrared radiation in the
atmospheric window or not the number of different ranges of wavelength they absorb is
caused by the molecules having different types of bonds; each type absorbs at its own frequency;
the intensity of the absorption e.g. methane has 4 C-H bonds which means it can absorb more at a certain frequency!
the abundance of the chemical the lifespan of the chemical
Greenhouse factor
Compares ability of a greenhouse gas to absorb IR to the same amount of carbon dioxide which has a factor of 1.
Example: greenhouse factor of methane is 30 which means it absorbs as much as 30 molecules of carbon dioxide or 1 molecule of methane absorbs 30 times more as 1 molecule of carbon dioxide.
greenhouse gas: CO2
Sources: Human: burning fossil fuels and wood, forest fires,
burning waste Natural: respiration, decay of organic matter, natural
forest fires
Relative effect: Most important greenhouse gas (50% contribution) because of its great abundance (second largest after water vapour) and the large range of wavelengths over which it absorbs IR.
Greenhouse gases: H2O
Sources: Human: combustion of hydrocarbons Natural: evaporation
Relative effect: 0.1 - Least effective in trapping radiation but is most abundant.
Greenhouse gases: CH4
Sources: Human: cattle farming, rice paddies (wet soil means any
organic matter in it is decomposed without oxygen) , petroleum and natural gas production.
Natural: digestive tracts of ruminants, cattle, bogs or marshes, bacterial fermentation – when organic matter is decomposed anaerobically, methane gas is produced.
Relative effect: 30 - Low abundance in atmosphere but it is more effective in absorbing infrared radiation, however, its atmospheric lifespan in the atmosphere is short.
Greenhouse gases: N2O
Sources: Human: use of nitrogen based fertilizers Natural: bacterial action
Relative effect: 150 - Very effective in absorbing radiation, fairly long atmospheric life.
Greenhouse gases: CFCs Sources:
Human: refrigerators, air- conditioning, aerosols in spraying cans, foaming agents
Natural: none!!!!
Relative effect: 10 000 – 25 000 - Very effective in absorbing radiation, long atmospheric life but low abundance.
Greenhouse gases: SF6
Human source: electrical insulators
Greenhouse effect: 24 000
Greenhouse gases
Effects of particulates particulates scatters and reflect the incoming sunlight
(visible and UV) so that less solar radiation enters the atmosphere;
particulates also cause a lowering of the temperature as they provide condensation nuclei around which water particles condense to form clouds reducing solar heating;
volcanic eruptions and large forest fires greatly increase the amount of particulates.