Download Greenhouse Effect - Southwest High School

Greenhouse Effect
Julia Porter, Celia Hallan, Andrew Vrabel Miles,
Gary DeFrance, and Amber Rose
What is the Greenhouse Effect?
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The greenhouse effect is a natural occurrence caused by Earth's atmosphere and the reflective
nature of Earth's surfaces.
The greenhouse effect determines how much solar energy reaches Earth, how much is
reflected away, and how much is trapped inside.
It is responsible for keeping Earth's surface temperature warm enough to support life.
Without the greenhouse effect, Earth's average surface temperature would be -18°C.
What Happens During the Greenhouse
Effect (Part 1)?
Earth's Atmospheric
"Window"
The transmissivity* of the
atmosphere varies based
on type of gas and the
wavelength of the
radiation. It has trouble
absorbing wavelengths of
350 to 750 nanometers.
Visible light waves
generally have
wavelengths from 400 to
750 nanometers, and so
are not absorbed.
Solar energy strikes
the atmosphere.
The radiation varies
in wavelength and
frequency.
Contains visible light, ultraviolet,
infrared, gamma rays,
X-rays,
and
more
1/3 of the energy is absorbed by the atmosphere.
Different gases absorb infrared and ultraviolet radiation of
different wavelengths and convert the energy to heat.
*Transmissivity is a measure of
how much atmospheric gases allow
radiation to pass through them.
1/3 of the
energy,
mostly in
the visible
spectrum,
reaches the
Earth
1/3 of the
energy is
reflected
away and
lost to
space.
What Happens During the Greenhouse
Effect (Part 2)?
Heat waves
are infrared,
and can be
absorbed by
the
atmospheric
gases,
trapping
heat inside.
The visible light
waves make it
through the
atmosphere and
hit Earth's
surface.
Half of the energy is absorbed by rocks, soil,
and other surfaces. The visible light waves are
then re-radiated as heat waves.
Re-Radiation
When greenhouse gases absorb
infrared and ultraviolet radiation,
they re-radiate the energy in
infrared heat waves with longer
wavelengths. Some of these
waves are radiated into space,
and the rest are radiated back to
Earth's surface. The main
function of the greenhouse effect
is not causing Earth to heat up
faster, but causing it to cool down
more slowly.
Half of the energy goes into causing water to
evaporate, photosynthesis, and causing
winds, ocean waves, and water currents.
Main Greenhouse Gases
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Water Vapor
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Not a harmful greenhouse gas
Carbon Dioxide (CO2)
burning fossil fuels, waste, trees/ wood,
other chemical reactions (such as when
cement is mixed)
○ Can be absorbed from the atmosphere be
plants during photosynthesis
○
Main Greenhouse Gases (continued)
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Methane (Ch4)
during the production/ transportation of
coal, natural gases, and oil
○ also from the decay of organic waste
(much of the time from sitting in landfills)
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Nitrous Oxide (N2O)
combustion of fossil fuels/ other solid
wastes
○ through agricultural and industrial
activities and production
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Main Greenhouse Gases (continued)
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Fluorinated Gases
○ Hydrofluorocarbons, perfluorocarbons, hexafluoride
○ these are the most common/ everyday things that
we use that contribute to the greenhouse effect
○ things such as the emissions from refrigerators, air
conditioning units, aerosols, foams, etc...
○ these are all very powerful, but emitted in such small
amounts that they only make up a fraction of the
emissions
Analysis:
● In total, the heat from sunlight of wavelengths 2.8, 3, 4, 8,9,10, and 1530 microns will be trapped in the Atmosphere by harmful greenhouse
gasses. Water vapor also traps a lot of radiation but also increases
reflectivity of the Earth, and so is beneficial where global warming is
concerned.
● O2 and O3 absorb a little of the visible spectrum (.38-.72ish microns)
and also, importantly, all ultraviolet radiation(<.38 microns)
● More than half of the infrared radiation (>.72 microns) is absorbed by
the other GHGs.
Albedo
● In simple terms, it is how much light a
surface reflects
● Based on a scale of zero to one, but can
also be stated as a percentage
● Albedo = scattered power/incident power
● a planet's albedo is really an average figure
determined by what the planet is made up of
● depends on...
○ the frequency of the incoming radiation
○ the distribution of the incoming radiation
○ the surfaces/ terrains that a planet is made up of
Stefan-Boltzmann Law
"Total Power/Radiation Incident per unit Surface Area
of the radiator is directly proportional to the
Temperature (ºK) of the radiator to the fourth power."
P=e
A (T4-Tc4)
e = The emissivity of the radiator. is always
between 0 (radiates no heat) and 1 (Blackbody).
= constant of proportionality/Stefan's constant
= 6.78*10-8 Wm-2K-4.
A = surface area
T = temp of radiator
Tc = temp of surrounding system
The lovely Ludwig Boltzmann and Joseph
Stefan, respectively.
How Radiators interact with surfaces
● Good emitters = good absorbers => same constant e used in both equations
● Emission depends on heat difference and works towards equilibrium, once T=Tc, there is no emission.
● Darker objects, higher emissivity
● Larger objects, higher emissivity
Intensity of Sun's Radiation Incident
on the Earth
Temp. of sun = 5773 K
Surface A of Sun = 4*3.14*696,0002 = 6.08e12 m
Star = Blackbody (or very close to it)
Avg. Temp. of Earth = 291.6 K
ZAP!!
so: e A(T4-Tc4) = 1*6.78e-8*6.08e12(57734-291.64)
= 4.58e20 Watts
Emissivity
The emissivity of an object is the ratio of the amount of heat
radiated by the object at a certain temperature to the
amount of heat radiated by a black body at the same
temperature.
The range of emissivity values is from 0 to 1. A black body
has an emissivity of 1.
Emissivity (continued)
Incident Energy=Reflected Energy+Absorbed Energy+Transmitted Energy
*if you set Incident Energy=100%...
100% = % Reflected Energy + %Absorbed Energy + %Transmitted Energy
*since Absorbed Energy=Emitted Energy, and %Emitted=Emissivity...
1 = Emissivity + Reflectivity + Transmissivity
*most objects have a very low transmissivity; thus Transmissivity=0
1 = Emissivity + Reflectivity
Emissivity Comparisons
Infrared vs. Visible light
● Metallic surfaces have a low emissivity and high
reflectivity for both infrared and visible light
● Some substances may have very different emission
rates in infrared and visible light
Metallic vs. Nonmetallic
● Metals have a low emissivity due to their high
reflectivity, and nonmetals have a high emissivity as
they have a low reflectivity.
● See the table on the next slide and remember:
"Incident Energy = 1 = Emissivity + Reflectivity"
Emissivity of Different Substances
Surface Heat Capacity
Heat capacity, or specific heat ("C"), is the
amount of energy it takes to raise a certain
amount of a substance by a certain amount of
temperature. In Q=mc T; the "c" is the specific
heat of the object.
Black Body
● A black Body is an ideal body that absorbs all types of
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electromagnetic wave at any frequency at any angle
A black body at thermodynamic equilibrium is an ideal
emitter
A black body at thermodynamic equilibrium emits a
specific kind of electromagnetic radiation called black
body radiation, The radiation is emitted according to
Plank's law, meaning that it has a spectrum that is
determined by the temperature alone
Black Body Radiation
Black-body radiation is the type of
electromagnetic radiation within or surrounding
a body in thermodynamic equilibrium with its
environment, or emitted by a black body held at
constant, uniform temperature. The radiation
has a specific spectrum and intensity that
depends only on the temperature of the body
Blackbody Radiation at Different
Temperatures
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Every blackbody absorbs and emits all wavelengths of radiation. The intensity with which it
emits different wavelengths varies based only on the temperature of the blackbody.
As the temperature increases, the "peak wavelength," the wavelength emitted with the
most intensity, gets shorter.
So what?
By measuring the intensity of the
wavelengths emitting from a
blackbody, scientists can calculate
the temperature. This is
especially helpful for astronomers,
who treat stars and planets as
blackbodies (even Earth!). When
the peak wavelength is in the
visible spectrum, the blackbody
glows different colors. For
example, if a star is glowing bright
red, astronomers know it is near
5000 K. If it is closer to yellow, it
is closer to 6000 K.
The intensity curve, or emission spectrum, is determined using Planck's law, which is a function whose only variable is temperature.
Wien's Law and Peak Wavelength of
Blackbody Radiation
Wien's Law states that the product of a blackbody's temperature and its peak wavelength are a constant.
(Peak Wavelength)x(Temperature in Kelvin) = 2.898x10^-3 meters = 2898 microns.
At room temperature, the
peak wavelength is 9.66
microns. It is way out of the
visible spectrum, which is
why room temperature
blackbodies don't glow.
Around 798 K: The Draper Point.
Blackbodies begin to glow dull
red.
5800 K: Approximate
temperature of the sun. Its
peak wavelength is about 0.5
microns.
Infrared
Infrared light lies between the visible and
microwave portions of the electromagnetic
spectrum. It can not be seen by humans but
can be sensed in the form of heat.
Infrared Radiation and Greenhouse
Gasses
Radiation is absorbed from the sun by the earth in the form
of visible light. Eventually the heat is re-emitted by the earth
in the form of infrared radiation. Certain gases in the
atmosphere have the property of absorbing infrared
radiation. Oxygen and nitrogen the major gases in the
atmosphere do not have this property. The infrared
radiation strikes a molecule such as carbon dioxide and
causes the bonds to bend and vibrate. The molecule gains
kinetic energy by this absorption of IR radiation. This extra
kinetic energy may then be transmitted to other molecules
such as oxygen and nitrogen and causes a general heating
of the atmosphere.
Bibliography
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http://webcache.googleusercontent.com/search?q=cache:_uKLIPLnADgJ:www.cmmap.
org/scienceEd/summercourse/summerCourse07/docs/02.RadiationBalance.
ppt+&cd=1&hl=en&ct=clnk&gl=us&client=firefox-a
http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_constant
https://pac-ibphys.wikispaces.com/surface+heat+capacity
http://tes.asu.edu/MARS_SURVEYOR/MGSTES/TES_emissivity.html
http://www.ecd.bnl.gov/steve/pubs/HeatCapacity.pdf
"Greenhouse effect." The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth
Lerner. 4th ed. Detroit: Gale, 2008. Student Resources In Context. Web. 28 Feb. 2013.
"Greenhouse effect." U*X*L Encyclopedia of Science. U*X*L, 2011. Student Resources In
Context. Web. 28 Feb. 2013.
"Remote Sensing: Absorption Brands and Atmospheric Windows." NASA Earth Observatory.
The Earth Observatory. Web. 1 Mar 2013.
Lienhard, John H.. "John Draper's Sister." Engines of our Ingenuity. Engines of our Ingenuity.
Web. 2 Mar 2013.
Pattison, G, and "Black Body Radiation." Physics. Egglescliff School. Web. 2 Mar 2013.
nssdc.gsfc.nasa.gov/planetary/factsheet/sunfact.html
hyperphysics.phy-astr.gsu.edu/hbase/thermo/stefan.html#c3
solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=OverviewLong
http://www.optotherm.com/emiss-physics.htm
http://www.elmhurst.edu/~chm/vchembook/globalwarmA5.html