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 effect Natural greenhouse effect: absorption of infrared radiation by natural greenhouse gases (CO 2 and H 2 O 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 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 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.

terminology 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 = a gradual increase in planet-wide temperatures

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.

Global warming: Global warming: evidence

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, years old

Global warming: CO 2 emissions

Global warming: methane emissions

Global warming Trends in greenhouse gas emissions

Greenhouse gases

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

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.

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 worst drought in Amazon

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.

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: 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.

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

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: 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: N 2 O Sources: Human: use of nitrogen based fertilizers Natural: bacterial action Relative effect: 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: – Very effective in absorbing radiation, long atmospheric life but low abundance.

Greenhouse gases: SF 6 Human source: electrical insulators Greenhouse effect:

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.