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 completely transparent to some wavelengths of radiation, while being completely absorbent aka opaque to others. This is particularly crucial when considering Greenhouse Gases, which are considered the key culprit to 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 (for wavelength) and “y” axis (for the % of radiation absorbed or scattered by gases). Wherever you see 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 gasses is allowed to simply pass right through them. The bottom panel represents Rayleigh Scattering, which we won't cover here.
- Looking at second panel of Figure \(\PageIndex{1}\) (Total absorption and scattering, which represents the total atmosphere… the sum of all of the gasses of the atmosphere) most visible light is _____________________ by the atmosphere.
- Absorbed
- Not Absorbed
Gasses that are mostly transparent to shortwave radiation (Visible Light and lower wavelengths… 0.7 µm and less) while being absorbent to longwave radiation (Infrared radiation, mostly above 0.7 µm) are called Greenhouse Gasses. These gasses play a crucial role in keeping Earth warm because they allow shortwave radiation to heat the earth up, while preventing longwave radiation from escaping to space.
- Looking back at the Absorption Spectrum, which of these gasses are greenhouse gasses?
- Water Vapor (H2O)
- Methane (CH4)
- Carbon Dioxide (CO2)
- Nitrous Oxide (NO2)
- All of these
- With the exception of a huge spike in absorption of radiation near 10 µm, the atmosphere is mostly transparent to wavelengths between ____________________. This is called the Atmospheric Window.
- 1 and 100 µm
- 5 and 20 µm
- 7 and 12 µm