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Environmental Chemistry Greenhouse effect, global warming,

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Presentation on theme: "Environmental Chemistry Greenhouse effect, global warming,"— Presentation transcript:

1 Environmental Chemistry Greenhouse effect, global warming,

2 Greenhouse effect Solar radiation being absorbed by Carbon Dioxide molecules and water vapors in the lower atmosphere. Covalent bond of molecules absorbs the solar radiation but also reflects it back to space.

3 List the main greenhouse gases and their sources, and discuss their relative effects. Water molecules are the main green house gas, but it does not affect global warming. Evaporation of Oceans and Lakes Carbon Dioxide- from burning fossil fuels. Raises Earth’s temperatures. Chlorofluorocarbons- 14% of global warming, from pollutants, refrigerants Methane- decay of organic matters

4 List the main greenhouse gases and their sources, and discuss their relative effects. Ozone O 3 – secondary pollutant in smog. Dinitrogen Oxide- fertilizer Sulfur hexafluoride- insulators in the electrical industry.

5 Discuss the influence of increasing amounts of greenhouse gases on the atmosphere. Earth’s temperature increases which results in changes of agricultural behavior such as crop yields Changes in environmental temperatures: fishes die... Rising sea levels from melting ice caps.

6 solar radiation spectrum


8 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 effect 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.

9 terms greenhouse effect greenhouse 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 WARMING global warming global warming = a gradual increase in planet-wide temperatures

10 Global warming: Global warming: evidence global temperatures since 1850s 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.

11 Global warming: Global warming: evidence

12 Global warming: Global warming: http// Thin slice of ice – gas bubbles are dark Ice core from 2874 m depth, 491 000 years old

13 Global warming: CO 2 emissions

14 Global warming: methane emissions

15 Global warming Trends in greenhouse gas emissions

16 Greenhouse gases

17 seasonal fluctuations of carbon dioxide The use (photosynthesis) and release (respiration) of carbon dioxide in the northern hemisphere (Mauna Loa) has a much greater impact on the global carbon dioxide concentration than the southern hemisphere because there is more land and therefore plants.

18 Greenhouse gases 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.

19 Atmospheric window

20 Global warming effects (1) An increase in temperature by almost 1.0 degree (world average) over last 100 years. The 10 warmest years have all occurred since 1998. World wide rise in sea levels resulting from partial melting of glaciers and polar ice caps and thermal expansion of water (as a result of heating). Changes in crop yields: some crops will grow better, other worse.

21 Global warming effects (2) Changes in distribution of commercial crops Changes in the distribution of pests and disease-carrying organisms e.g. malaria. More 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

22 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

23 greenhouse gas: CO 2 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.

24 greenhouse gases definition Greenhouse 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.

25 Greenhouse gases: H 2 O Sources: Human: combustion of hydrocarbons Natural: evaporation Relative effect: Least effective in trapping radiation but is most abundant.

26 Greenhouse gases: CH 4 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: Low abundance in atmosphere but it is more effective in absorbing infrared radiation, however, its atmospheric lifespan in the atmosphere is short.

27 Greenhouse gases: N 2 O Sources: Human: use of nitrogen based fertilizers Natural: bacterial action Relative effect: Very effective in absorbing radiation, fairly long atmospheric life.

28 Greenhouse gases: CFCs Sources: Human: refrigerators, air- conditioning, aerosols in spraying cans, foaming agents Natural: none!!!! Relative effect: Very effective in absorbing radiation, long atmospheric life but low abundance.

29 Greenhouse gases

30 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.

31 Ozone Depletion Ozone is the layer that protects Earth’s surface from harmful ultra-violet radiation

32 Ozone Depletion The Oxygen-Oxygen bond in Ozone is weaker to the double bond in O 2, The bonds in oxygen and ozone are both broken when they absorb enough UV radiation Ozone is depleted mainly by CFCs

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