2.3: Selective Absorbers and Greenhouse Gasses
- Page ID
- 39711
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Absorption by the Atmosphere
Most of the key gases in the atmosphere are called Selective Absorbers, meaning they are entirely transparent to some wavelengths of radiation while completely absorbent (i.e., opaque) to others. This is particularly crucial when considering Greenhouse Gases, which are widely regarded as the key culprits in Global Warming.
To understand which gases absorb which wavelengths of radiation, we must look at the absorption spectrum, Figure \(\PageIndex{1}\). Here's how to read this: There are eight panels, each with the same “x” axis (wavelength) and “y” axis (% of radiation absorbed or scattered by gases). Wherever you see a grey area in the second panel, it represents absorption happening at that wavelength. Meanwhile, for panels 3-7, the amount of colored area represents the percentage absorbed. For example, Oxygen and Ozone absorb almost 100% of radiation between 0.2-0.3µm (200-300nm). These wavelengths actually fall in the Ultraviolet category. This should make sense because our Ozone layer absorbs ultraviolet rays, thus protecting us from them. It can also be assumed that radiation not absorbed by these gases passes right through them. The bottom panel represents Rayleigh Scattering, which we won't cover here.
- According to the second panel in Figure \(\PageIndex{1}\) (Total absorption and scattering, which represents the total absoprtion from all of the gases of the atmosphere) most visible light is __________ by the atmosphere.
- Absorbed
- Not Absorbed
Gases that are mostly transparent to shortwave radiation (visible Light and shorter wavelengths… 0.7 µm and less) but absorb longwave radiation (Infrared radiation, mostly above 0.7 µm) are called Greenhouse Gasses. These gases play a crucial role in keeping Earth warm because they allow shortwave radiation to heat the Earth, while preventing longwave radiation from escaping to space.
- According to the Absorption Spectrum, which of these gases are greenhouse gases?
- Water Vapor (H2O)
- Methane (CH4)
- Carbon Dioxide (CO2)
- Nitrous Oxide (NO2)
- All of these
- Except for a massive spike in absorption of radiation near 10 µm, the atmosphere is mainly transparent to wavelengths between _________. This is called the Atmospheric Window.
- 1 and 100 µm
- 5 and 20 µm
- 7 and 12 µm