Besides carbon dioxide, human breath contains so-called volatile compounds. 872 of these are now known to scientists. A few know that they are produced by physiological processes in the body. This knowledge is used to measure changes in the body, for example, how the organism reacts to sport or to certain foods. Strong emotions also trigger biochemical processes in the muscles, nervous system, or blood circulation. Prof. Jonathan Williams and his team from the Max Planck Institute for Chemistry in Mainz wanted to find out whether these reactions could be detected in the air.
A cinema offers the ideal setting for this project. On the one hand, all viewers react to the film events at the same time. This means that the measured values can always be assigned to a specific scene. In addition, the halls are continuously ventilated: fresh air enters through openings under the seats, while the "used" air escapes through ventilation openings in the ceiling.
The scientists installed several mass spectrometers there and were thus able to measure the concentration of around 100 different volatile compounds at intervals of 30 seconds. The continuous circulation also has the useful side effect that the composition of the air quickly returns to a normal level after the performance. This makes it easy to compare the results of successive measurements later on.
Over one and a half months the values were measured in two halls of a multiplex cinema in Mainz. During this period, films of various genres were shown: in addition to the usual comedies and action films, horror, and children's films were also shown - even a ballet performance was among them. The spectrograms of the individual curves were so characteristic that the researchers could often see with the naked eye which film was involved. Especially exciting and funny scenes can be clearly recognized by the measurement curves.
"When the heroine fought for her life at the height of an action movie, the values for carbon dioxide and isoprene in the exhaust air always rose significantly," Williams explains. "...at every performance." This is important because only in this way the results are reproducible, i.e., scientifically reliable. Isoprene is known to be released through muscle activity. One explanation for the increase in isoprene concentration in a seated audience could be that moviegoers get tense, restless, and breathe faster during exciting scenes. Scientists at the Max Planck Institute used IR spectroscopy to measure the carbon dioxide concentration in the cinema auditorium. Gases absorb certain wavelengths of the IR spectrum. Based on the absorption behavior, a sensor can precisely determine the CO2 content.