Climate change is currently an eminent theme in politics.
Thereby, so-called greenhouse gases such as CO2 are considered as the real
cause for the temperature rise of the global atmosphere. This theory traces
back to measurements of Tyndall at the end of the 19th century which revealed
that CO2 absorbs thermal radiation, in contrast to N2 and O2, the main
components of the air, which do not absorb. Subsequently, Arrhenius tried to
theoretically implement the Stefan-Boltzmann law, which meanwhile became known,
assuming that the atmosphere is warmed up by the black-body radiation of the
Earth surface, but solely due to the CO2 and to similar IR (infrared) absorbing
greenhouse gases such as CH4. This means: The atmosphere would not be warmed up
if no CO2 or other greenhouse gases were there. Thus the temperature of the
atmosphere would be identical with the temperature of the absolute zero. After
the Second World War, this approach was continued by Plass and others, based on
IR- spectroscopic, and regarding an extra-terrestrial albedo or solar
reflection coefficient.
However, such an extra-terrestrial reflection coefficient
for solar light, which implicates a viewpoint outside of the atmosphere, cannot
be exactly defined since various effects are occurring within the atmosphere,
for instance turbulences by winds. They cannot be expressed by a simple
coefficient given by the ratio between emitted light and incident light.
Moreover, by means of the usual determination methods, applying radiative field
measurements, no reliable values for the terrestrial albedo were available,
since the incident sunlight is independent of the distance to the surface,
whereas the emitted light depends on the distance.
In contrast, the method developed by the author and
described in the first enclosed article entitled »The solar-reflective
characterization of solid opaque materials« enables the direct determination of
the – colour dependent – solar absorption coefficient, thus of the complement
of the solar reflection coefficient. This determination is feasible with a
lab-like method by measuring the temperature increases of well-characterized
plates, preferably from aluminium, during a permanent solar irradiation period.
Since any solid plate emits thermal radiation when its temperature is
increasing, a constant limiting temperature is reached when the intensity of
the emitted radiation is identically equal to the intensity of the emitted
radiation. Since this limiting temperature could not be achieved within the
measuring period of 30 minutes when 20 mm thick aluminium plates were used, due
to their high heat capacity, separate cooling down measurements were made in a
darkened room, which enabled a mathematical modelling of the whole process and
a determination of the – colour dependent - limiting temperatures. Besides the
evaluation of the colour-specific solar absorption coefficients, this method
also enables studying the influence of other factors affecting the warming up
process, such as the heat capacity of the plates or the convection of the air.
A second, even graver flaw in conventional atmospheric
physics arises from the fact that, with regard to the interactions between
infrared light and gases, solely the light absorption was measured, but never
the warming-up that is the temperature rise of irradiated gases. For the usual
IR-spectroscopic application, whereby specific bonds in organic molecules can
be identified, those features are not relevant. However, in this case where the
temperature represents the relevant parameter, it should have been a peculiar
requirement to gather empirical facts in order to ascertain the theoretical
assumptions. But incredibly enough, this has never been done so far. Hence it
was the subject of the author’s further work, described in the second enclosed
article entitled »The thermal behaviour ofgases under the influence of
infrared-radiation«, and delivering surprising results which entirely
contradicted the former conventional perception.
The particular difficulty at this measuring problem arises
from the very low heat capacity of gases, which runs the risk that the
measurement results are interfered by the measuring vessel ore tube. Moreover,
the walls of the vessel or tube may directly be warmed up by the (IR) light,
which has to be used for the irradiation of the gas, indirectly influencing the
gas temperature. This problem could be widely solved by using quadratic (25 cm
x 25 cm) 1 m long tubes from Styrofoam which were mirrored with thin aluminium
foils and covered by thin transparent plastic foils on both ends. The
temperatures were measured at three different positions with mirrored
Hg-thermometers. Besides sunlight, mainly IR-spots were used as radiation
sources. However, in the latter case an inherent intensity loss along the tube
could not be eliminated but solely minimized.
Such a simple apparatus may appear unprofessional and not
suited for modern research work. However, it is indeed adequate to the problem,
although it necessitates only simple materials which are partly available in
do-it-yourself shops. But these materials were not available at the time when
the pioneer work was done, whereas the professional IR-spectrometers are not
suited for this measuring problem since they were constructed for another,
analytical purpose. Besides, one should be aware that many trials were needed
in order to optimize the apparatus and to obtain reliable results, and that the
measurements required considerable skill.
Surprisingly, these results revealed that all gases absorb
infrared radiation, even noble gases. Thereby they are warmed up to a limiting
temperature where the intensity of the absorbed radiation was identically equal
to the intensity of the emitted radiation by the gas. Moreover, air (or a 4:1
N2/O2 mixture) and pure carbon-dioxide were warmed up to a nearly equal extent.
Solely in the line Argon – Neon – Helium significant differences appeared. Applying
the kinetic gas theory, the radiation intensity of the emitted light turned out
to be proportional to the collision frequency of the particles (atoms or
molecules). When the particle size of different gases is unchanged, the
collision frequency is proportional to the gas pressure and to the square root
of its absolute temperature. Comparing the results obtained under sunlight with
those obtained with artificial light, and applying Planck’s
temperaturedependent radiative distribution law, the effective wave length was
roughly estimated at 1,9 μm.
This behaviour can be explained by the occurrence of an
internal energy of the molecules or atoms, which is due to vibrations of the
atom nuclei or of the electron shells, and which is induced by the applied
IR-radiation. That kind of energy is not identical with the apparent heat of
the gas which is measurable with a thermometer, and which is due to the kinetic
translation energy of the entire atoms or molecules. Thus, when the particles
are in an excited vibrational state, induced by thermal radiation, solely a
part of this internal energy is transformed into apparent heat, induced via
collisions, whereas another part is emitted as radiation, without having
achieved a change of apparent heat. Contrariwise, warming up of a gas leads to
acceleration of the particles, and via collisions to enhanced internal
vibrations enabling thermal radiation.
Obviously, in this case the amount of absorbed IR-radiation
is so low that it cannot be detected with a conventional IR-spectrometer.
However, it is high enough to induce a measurable temperature increase. On the
other hand, the absorption values obtained with IR-spectroscopic methods appear
to be irrelevant for a temperature enhancement, since that kind of adsorption may
possibly lead to internal vibrations which cannot be readily converted to
apparent heat but rather to a radiation emission.
As a consequence of the theoretical finding that the thermal
radiation of a gas was proportional to the pressure, one could assume that the
atmosphere emits thermal radiation in both directions, namely towards Space as
well towards the Earth surface, and that the intensity of the atmosphere
radiation at the Earth surface was proportional to the atmospheric pressure and
to the square root of the absolute temperature of the atmosphere at the Earth
surface. Thus in the case of a steady equilibrium state the intensity of the
black-body radiation of the Earth surface – or of a particular section of it –
must be equal to the intensity of the thermal atmospheric radiation which may
be called counter-radiation. This approach is similar to the approach of the
Stefan-Boltzmann relation. However, it is more expressive since it comprises
the pressure as a predominant parameter, whereas in the Stefan-Boltzmann relation
solely the absolute temperature appears (in the fourth power). Thereby no
information is given as to how this temperature is achieved.
Thus, in the third
enclosed article entitled »The Thermal Radiation of the Atmosphere and its Role
in the so-called Greenhouse Effect« it stood to reason to validate this
approach by empirical evidence, (1) by using the method described in the first
article where coloured aluminium plates were exposed to sunlight, and (2) by
varying the atmospheric pressure by means of varying the sea level of the
measurement station. Thereby, the steady states at the limiting temperatures
were needed where the intensity of the emitted thermal radiation of the plates
is equal to the intensity of the counterradiation of the atmosphere. In order
to get the real limiting temperatures (and not the computed ones), thinner
aluminium plates were used (8 mm thick, instead of the original 20 mm ones)
which entailed shorter measurement periods.
In order to get optimal results, it would be necessary to
solely vary the atmospheric pressure whereas the other parameters (atmospheric
temperature and intensity of the sunlight) should be invariant. However, in
reality this condition can inherently not be fulfilled since the variation of
the sea level of the measuring station implicates a variation of the
temperature of the ambient atmosphere as well of the intensity and the
character of the sunlight. Thereby, at higher sea levels the atmospheric
temperature decreases whereas the intensity of the sunlight increases.
Nevertheless, acceptable results were obtained with four differently coloured
plates (white, blue, green and black) at the two measuring stations in
Switzerland Glattbrugg (430 m above sea level, approx. 0.948 bar atmospheric
pressure) and Furka-Pass (2430 m above sea level, approx. 0.738 bar atmospheric
pressure), yielding a so-called atmospheric emission constant A of approx. 22
Wm-2bar-1K-0.5.
Author (s) Details
Thomas Allmendinger
Independent Scholar, ETH (Swiss Federal Institute of Technology), Zurich, Switzerland.
View Book: - http://bp.bookpi.org/index.php/bpi/catalog/book/155
Thomas Allmendinger
Independent Scholar, ETH (Swiss Federal Institute of Technology), Zurich, Switzerland.
View Book: - http://bp.bookpi.org/index.php/bpi/catalog/book/155
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