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.