1. Selective Absorption by Water Vapor and Carbon DioxideWater vapor
and carbon dioxide are the two gases that absorb the most longwave
radiation emitted by the surface (see Figure 3-10). Why are these gases
so selective, being nearly transparent for shortwave radiation but
nearly opaque for longwave? Recall from Chapter 2 that isolated atoms
have discrete energy states, with only certain energy states possible.
As energy is absorbed and emitted by a gas molecule, its energy state
rises and falls by discrete amounts from one allowable state to another.
We have also seen that the energy associates with a photon of radiation
is discrete and depends on its wavelength. Knowing the wavelength, we
know the energy level of the photon.It must be, therefore, that gas
molecules absorb only certain photons, namely, those that push the
molecule into allowable energy states. Photons with higher or lower
energy values will not be absorbed but will instead pass through the
gas. Because a unique wavelength is associated with every energy level,
this is equivalent to saying that only certain wavelengths can be
absorbed by any particular gas. (The same is not true of liquids and
solids, whose molecules interact to give much more continuous
absorption.) Whether or not a particular wavelength can be absorbed
depends on the molecular structure of the absorber (the configuration of
electrons, etc.) As it happens, the gases in the atmosphere do not have
strong absorption bands in the visible part of the spectrum. But some
of them, including water vapor and carbon dioxide, do have molecular
structures that permit absorption of longwave radiation. Combined, the
various gases absorb most of the longwave energy passing through the
atmosphere.Which two gases are most effective at absorbing longwave
radiation? Get solution
2. Selective Absorption by Water Vapor and Carbon DioxideWater vapor and carbon dioxide are the two gases that absorb the most longwave radiation emitted by the surface (see Figure 3-10). Why are these gases so selective, being nearly transparent for shortwave radiation but nearly opaque for longwave? Recall from Chapter 2 that isolated atoms have discrete energy states, with only certain energy states possible. As energy is absorbed and emitted by a gas molecule, its energy state rises and falls by discrete amounts from one allowable state to another. We have also seen that the energy associates with a photon of radiation is discrete and depends on its wavelength. Knowing the wavelength, we know the energy level of the photon.It must be, therefore, that gas molecules absorb only certain photons, namely, those that push the molecule into allowable energy states. Photons with higher or lower energy values will not be absorbed but will instead pass through the gas. Because a unique wavelength is associated with every energy level, this is equivalent to saying that only certain wavelengths can be absorbed by any particular gas. (The same is not true of liquids and solids, whose molecules interact to give much more continuous absorption.) Whether or not a particular wavelength can be absorbed depends on the molecular structure of the absorber (the configuration of electrons, etc.) As it happens, the gases in the atmosphere do not have strong absorption bands in the visible part of the spectrum. But some of them, including water vapor and carbon dioxide, do have molecular structures that permit absorption of longwave radiation. Combined, the various gases absorb most of the longwave energy passing through the atmosphere.Why is it that gases do not absorb all wavelengths of energy? Get solution
2. Selective Absorption by Water Vapor and Carbon DioxideWater vapor and carbon dioxide are the two gases that absorb the most longwave radiation emitted by the surface (see Figure 3-10). Why are these gases so selective, being nearly transparent for shortwave radiation but nearly opaque for longwave? Recall from Chapter 2 that isolated atoms have discrete energy states, with only certain energy states possible. As energy is absorbed and emitted by a gas molecule, its energy state rises and falls by discrete amounts from one allowable state to another. We have also seen that the energy associates with a photon of radiation is discrete and depends on its wavelength. Knowing the wavelength, we know the energy level of the photon.It must be, therefore, that gas molecules absorb only certain photons, namely, those that push the molecule into allowable energy states. Photons with higher or lower energy values will not be absorbed but will instead pass through the gas. Because a unique wavelength is associated with every energy level, this is equivalent to saying that only certain wavelengths can be absorbed by any particular gas. (The same is not true of liquids and solids, whose molecules interact to give much more continuous absorption.) Whether or not a particular wavelength can be absorbed depends on the molecular structure of the absorber (the configuration of electrons, etc.) As it happens, the gases in the atmosphere do not have strong absorption bands in the visible part of the spectrum. But some of them, including water vapor and carbon dioxide, do have molecular structures that permit absorption of longwave radiation. Combined, the various gases absorb most of the longwave energy passing through the atmosphere.Why is it that gases do not absorb all wavelengths of energy? Get solution
