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33 Cards in this Set
- Front
- Back
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What would be the mathematical equation for the Beer-Lambert Law normaly used in tropospheric chemistry? |
I/I0=e^(-deltaNL) where delta is the absorption cross section N: concentrtaion L: path length I: Intensity |
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What can be a term to refer to (N*delta*L) of a medium? |
The optical depth. |
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What is the more common beer-Lambert law expression for chemistry? |
A=epsilon*C*L C= mol/L Epsilon= molar absorptivity A=absorbance L=path length. |
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Regarding the absorbance, what is the mathematical relationship it has with transmittance? What is transmittance equivalent to? |
A=-Log(T) T(transmittance)=I0/I |
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How could you determine delta of a gas in a labe ( regarding Beer lambert law)? What do you have to keep in mind regarding delta ( its measurement?) |
Put a gas in a chamber of known length and measure transmittance. Then change concentration (ie pressure) in the chamber. By doing a linear regression of the concentration and transmittance you will obtain a slope that is = to delata*L. devide by chamber length and you find delta This only gives you delta FOR ONE WAVELENGTH |
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Absorbance of a cumulation of gases in a chamber has what property? |
They are additive. |
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How may you find the concentration of a compound of 1000 Pa and 1 Pa in a same container? |
Use Pv=NRTwhere v=1 M3 and R = 8.314 |
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How do you get the absorbance at base 10 ? |
Abase10=Abase(e)/Ln(10) |
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What is the best way to understand a cross section of a molecule? |
if you had a 2D representation of a molecule, what would be the surface area where light would be absorbed : larger surface, more absorption for a given absorption coefficient. |
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What do you have to keep in mind regarding the Beer-Lambert's law in the atmosphere? |
The light source is the sun which encompasses many factors which must be taken into consideration |
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What are the problems regarding the Beer-Lambert's law if you assume light from the sun = I0 and light at earth's surface = I?(4) |
1: Absorptions occurs from multiple species (always) 2: Scattering will occur at all wavelengths 3: The concentration of all species varies with altitude 4: Path length varies with the Sun's position |
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What is the Mathematical equation for the solar zenith? |
M= actual Pathlength/ vertical pathlength ~ L/h = 1/ cos(teta) M is termed the air mass even if it does not have a dimention. |
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At what angle would the sun zenith no longuer be valid and why? |
At larger angles than 80 degrees because the earth's curvature and refraction starts to matter. |
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What is extinction? |
It is the sum effect of scattering and absorbance of an incoming light source. |
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A red light and blue light are subject to the atmosphere's scattering. What will be the observed difference between the two? |
Red light will be less scattered and hence have a higher intensity than the blue light. This is because short wavelengths tend to scatter more strongly. |
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What will be the phenomenons respoonsible for light scattering by an aerosol particle? |
Reflection Refraction Internal reflection Diffraction |
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Why is the sky blue? |
This is because of Rayleigh Scattering. Blue light will be largely scattered from the sun's light and hence the large color you will observe from any angle will be blue light. |
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What is the modified Beer-lambert law for the atmosphere? |
i/i0=exp(-tm) where m= air mass (zenith) t= optical depth ( N*delta*L) |
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In reality, the expression t (optical depth) in the beer-lambert law will be a sum of what? |
tsg+tag+tsp+tap where: tsg+tag=scattering and absorption of gases tsp+tap=scattering and absorption of particles |
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When is an absorbing layer considered optically thin? thick? |
when t=0->thin-> no absorption when T is very large->thick-> ALOT of absorption |
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What is the mathematical expression for the column abundance? ( and units) |
integral from z(=0 to TOA) of N(z)dz ( units are molecules/cm^2) |
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What is the concentration profile of air? |
nair(z)=Nair(0)exp(-z/H) |
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What is the values of nair(0) and H typically? (on earth) |
Nair(0)=2.55 x 10^19 molecules/cm^3 H= 7.4km |
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What would be the value of O2 for nair(0)H? |
for air= 2.55810^19 mole./cm^3 * 7.4km O2 have coefficient of 21% hence you multiply above by .21 |
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What would be t of O2 ( absorption?) |
t= delta * (.21 * nair(0) * H(this is a constant)) |
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lambda = 240 nm. i/i0=0.0082 measured directly overhead. what is cross section? |
M = 1 hence 0.0082=exp(-delta(4.0x10^24)) hence delta= -ln(0.0082)/4.0x10^24 |
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Why can<t the absorption of O3 be expressed in the same way as O2? |
Because O3 concentrationdoes not follow similar profile as O2 |
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What is the dobson unit? |
unit of absorption for O3. |
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What is the dobson unit equivalent to ? |
2.69*10^16 molecules/cm^2 |
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What is the average absorbance at the hartley huggins and chappuis bands? |
Hartley: 80 Huggins:.8 Chappuis:.024 |
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wavelength 300 nm; 45degrees zenit, transmittance = 0.026. if all from O3, what is column abindance in DU |
0.026=exp(-mt) m=1/cos(45)= sqrt(2) t=- ln(0.026)/sqrt(2)=2.58 A=2.58/3.2x10^-19/2.69x10^16=300DU |
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What is the surface albedo an dwhat is it dependent on? |
Albedo=reflected radiation/ incident radiation albedo is dependent on the wavelength. |
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How does the greenhouse effect work? |
Light from the sun goes through the atmosphere ( visible spectrum wavelengths mostly) when it hits the earth, it is either basorbed or reflected in the form of infrared. This in turn is absorbed MUCH MORE by several gases in the atosphere. Hence, you have greenhouse gases |
