A determination of the greenhouse parameter for dry and unpolluted air



The relative extinction of solar and infrared radiation by dry and clean air molecules, has been estimated through a theoretical determination of the ratio referred ordinarily as the Greenhouse Parameter (GP). In a first approach, it was calculated assuming that terrestrial air only consists of a simple mixture of oxygen and nitrogen. The method used here is based on the application, in an inverse procedure, of an homogeneous, plane-parallel, and time-independent grey model, which employs the Eddington approximation as a solution to the radiative transfer equation, both in the solar and the infrared spectral regions and, which has the GP value as an input free parameter. The best value of the GP was estimated calibrating the local temperature profile for four types of uniform surface (snow, desert, vegetation and ocean), with average albedos known in these spectral regions, adopting air surface temperature values which were chosen for an assumed micro or local climatological environment according to an average radiative criterion. With this result, it was possible for an estimation of the infrared opacity for the air layer implicated in this model and also the mean extinction coefficient in this spectral range to be calculated. The results predicted are compared with results obtained indirectly from the data provided by other authors. Although its validation is constrained solely to the radiative model applied it seems that the value of the GP obtained is more accurate than the one initially available.

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