Novel Discoveries in Atmospheric Physics | Book PI International

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. As a consequence, it can be stated that the counter radiation of the atmosphere indeed contributes to the climate, but as a whole and insofar as the atmospheric temperature decreases at higher sea levels. Thereby the trace gas is insignificant. Furthermore, it can be supposed that the mean temperature of the Earth surface would decrease when, as a result of a reduced assimilation of plants, the oxygen-content of the atmosphere and therefore the atmospheric pressure would generally decrease since the nitrogen-content can be assumed to be constant. This may possibly explain – or at least partly – climate changes during earlier palaeontology aeons. But in particular, it reveals the important role of nitrogen in the atmosphere, which does not only reduce the chemical aggressiveness of oxygen, but, due to the thereby enhanced atmospheric pressure, it also enables an overall convenient climate, which is prerequisite for life on this earth.

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