For our studies of the greenhouse gas emission – different to a simpler experimental set-up with a horizontally positioned Styrofoam box described in Part I – here we use an arrangement consisting of a vertically placed cylinder with uniformly heated walls and an opening at the bottom, which is sealed by an infrared-transparent foil. Below this foil are two calibrated radiation sensors on a cooled plate, which measure the radiation emerging from the cylinder. At the same time, the temperature distribution in the container is recorded before and after adding a greenhouse gas.
With this set-up we have investigated the gases water vapor, CO2, CH4, N2O, and Freon 134a at varying concentrations between 1–8% in air and at normal pressure. The radiation emitted by the gases can be detected against a larger background radiation originating from the cylinder walls. All gases show strong saturation effects with increasing concentration. The measurements can be well reproduced by corresponding radiation transfer calculations. A clear influence of water vapor on the other gases is also evident as increased background radiation and partial spectral superposition with these gases, which appears as attenuated emission of these gases. Likewise, with increasing radiation—particularly for the stronger greenhouse gases—simultaneous cooling of the gases across the cylinder volume can be observed. This is explained by conversion of kinetic and thus thermal energy into radiation, which can escape through the infrared transparent foil.
For a gas layer located above a cooler subsurface, as known from inversion weather conditions or as observed in the Arctic and Antarctic during the winter months, the radiant power emitted by the surface and partially absorbed by the warmer gas layer, is lower than the power emitted upward. This corresponds to a negative greenhouse effect, which with the presented set-up can be reproduced for the first time in the laboratory.