What Type of Gases Strongly Absorb Outgoing Longwave Radiation and Re-emit It Again as Heat
In 1827, Joseph Fourier, a French mathematician and physicist, wondered why Earth'due south boilerplate temperature is approximately xv°C (59°F). He reasoned that there must be some type of remainder between the incoming energy and the outgoing free energy to maintain this adequately constant temperature. His calculations indicated that World should actually be much colder (-xviii°C or 0°F).
To have an average temperature of fifteen°C (59°F), Fourier knew that at that place had to be another process occurring in the atmosphere –– something similar to the way a greenhouse retains heat. A greenhouse's glass enclosure allows visible lite to enter and be absorbed by the plants and soil. The plants and soil then emit the absorbed heat energy as infrared radiation. The glass of the greenhouse then absorbs that infrared radiation, emitting some of information technology back into the greenhouse and thus keeping the greenhouse warm even when the temperature outside is lower.
Because the 2 processes are similar, the name "greenhouse effect" was coined to draw Fourier's explanation. Yet, function of a greenhouse's warmth results from the physical barrier of the glass, which prevents the warmer air from flowing outward. So despite the fact that the atmospheric greenhouse upshot has some processes in common with an actual greenhouse, the overall mechanisms driving the greenhouse consequence are unlike and more complex.
Greenhouse Gases
Y'all take already learned that Earth's atmosphere is composed primarily of nitrogen and oxygen. These gases are transparent to incoming solar radiation. They are likewise transparent to approachable infrared radiations, which means that they practice not absorb or emit solar or infrared radiations. However, there are other gases in Earth's atmosphere that practise absorb infrared radiation. These gases are known equally greenhouse gases. Beneath are the most important greenhouse gases that influence Earth'due south climate organisation.
Water vapor (Water) is the strongest greenhouse gas, and the concentration of this gas is largely controlled by the temperature of the atmosphere. As air becomes warmer, it tin hold more moisture or water vapor. When the air becomes saturated (or holds every bit much moisture as the air tin can at that temperature), the excess moisture volition condense into cloud aerosol. And if these aerosol are large enough, they will autumn as atmospheric precipitation.
Carbon dioxide (CO2) is also an important greenhouse gas. Information technology has a long lifetime in Earth's temper. Carbon dioxide strongly absorbs energy with a wavelength of fifteen μm (micrometers). This makes carbon dioxide a adept absorber of wavelengths falling in the infrared radiation region of the spectrum.
Carbon dioxide constantly moves into and out of the temper through 4 major processes: photosynthesis, respiration, organic decomposition or disuse, and combustion or the called-for of organic material. You will learn more about carbon dioxide and the carbon cycle in Module 4.
Methane (CH4) is 30 times stronger than carbon dioxide every bit an cushion of infrared radiation. Methane, all the same, is present in smaller concentrations than carbon dioxide, and then its internet contribution to the greenhouse effect is not every bit large. Methyl hydride is besides relatively curt-lived (lasting approximately 8 years) in the atmosphere. Methane is produced when bacteria decompose organic plant and animate being thing in such places equally wetlands (e.g., marshes, mudflats, flooded rice fields), sewage treatment plants, landfills, and the guts of cattle and termites. Scientists are concerned most the concentration of methane increasing in regions where the Arctic and alpine permafrost is thawing and releasing methane as it warms.
Halocarbons are composed of carbon, chlorine, fluorine, and hydrogen. They include chlorofluorocarbons (CFCs), which are human being-made gases commonly used in refrigerators and air conditioners. Concentrations of Chlorofluorocarbon gases in the temper are the highest of whatever of the halocarbons, and they tin can absorb more infrared radiation than any other greenhouse gas. The impact of one molecule of a Cfc gas is equivalent to ten,000 molecules of carbon dioxide.
Nitrous oxide (N2O), a relatively long-lived gas, has increased in atmospheric concentration due mainly to agriculture. Nitrate (NO3-) and ammonia (NH4+) are used as fertilizers. Bacteria convert a small amount of this nitrate and ammonia into the form of nitrous oxide. Internal combustion engines as well produce nitrous oxide.
Ozone (O3) is also a relatively pocket-size greenhouse gas because it is found in relatively low concentrations in the troposphere (the everyman layer of the temper). In the troposphere, it is produced by a combination of pollutants — mostly hydrocarbons and nitrogen oxide compounds.
In the 1860s, John Tyndall, an Irish scientist who was fascinated by the growth and formation of glaciers, wanted to examination his ideas explaining how Earth maintained a fairly constant temperature. He began a serial of experiments to measure the amount of radiant heat (infrared radiation) that certain gases could absorb and transmit. Tyndall found that water vapor and carbon dioxide were good absorbers and emitters of infrared radiation.
The relative importance of a greenhouse gas depends on its affluence in Earth's atmosphere and how much the gas can absorb specific wavelengths of energy.
An constructive absorber of infrared radiation has a broader absorption profile, which means that it tin can blot a wider spectrum of wavelengths. Water vapor and carbon dioxide tin can absorb radiation wavelengths in the range of 4 μm to 80 μm, except those between viii μm and 12 μm. Ozone tin can absorb wavelengths between 9 μm and ten μm, but as you take learned, it is institute in low concentrations. The dominicus'south ultraviolet wavelengths are strongly absorbed past ozone in the stratosphere.
How the Greenhouse Effect Works
The sun's visible wavelengths of radiation pass easily through the temper and reach Earth. Approximately 51% of this sunlight is absorbed at Globe'due south surface past the country, water, and vegetation. Some of this energy is emitted back from the Earth'south surface in the class of infrared radiation.
Water vapor, carbon dioxide, methane, and other trace gases in Earth'south atmosphere absorb the longer wavelengths of outgoing infrared radiation from Earth's surface. These gases so emit the infrared radiation in all directions, both outward toward space and down toward Globe. This process creates a second source of radiation to warm to surface – visible radiations from the sun and infrared radiation from the atmosphere – which causes World to exist warmer than it otherwise would be. This process is known as the natural greenhouse result and keeps Globe's boilerplate global temperature at approximately 15°C (59°F).
I. The sun's visible wavelengths of radiation laissez passer easily through the atmosphere and attain Earth. Approximately 51% of this sunlight is absorbed at Globe's surface by the land, h2o, and vegetation.
II. Some of this energy is emitted from Globe's surface back into infinite in the form of infrared radiation.
III. Much of this infrared radiation does not reach space, all the same, because information technology is captivated by greenhouse gases in atmosphere, and is and so emitted every bit infrared radiation back toward the Earth's surface. This process is known as the greenhouse upshot.
If the concentration of greenhouse gases increases, and so more infrared radiation will exist absorbed and emitted back toward Globe's surface, creating an enhanced or amplified greenhouse issue.
 | |
| Certain human activities emit boosted greenhouse gases to the atmosphere and increase the amount of heat that gets absorbed before escaping to space, thus enhancing the greenhouse upshot and amplifying the warming of the earth. | |
When averaged over the class of a yr, the corporeality of incoming solar radiation received from the sun has balanced the corporeality of outgoing energy emitted from Globe. This equilibrium is called Earth's energy or radiations balance. Relatively pocket-sized changes in the amounts of greenhouse gases in Earth's atmosphere can profoundly alter that balance between incoming and outgoing radiations. Earth then warms or cools in order to restore the radiative residue at the top of the atmosphere.
Source: http://www.ces.fau.edu/nasa/module-2/how-greenhouse-effect-works.php
0 Response to "What Type of Gases Strongly Absorb Outgoing Longwave Radiation and Re-emit It Again as Heat"
Post a Comment