Cinema/Movie Theater

All data were recorded at the Cinestar Cinema complex in Mainz (Fig. 4a), Germany between 1st December 2013 and 14th January 2014. Of the 14 screen multiplex, two separate screen rooms were used (see Fig. 4b, Cinema 2 capacity 230 and Cinema 7 capacity 230). During a film the entrance doors were closed and ambient air was circulated from outside into the room through vents under the banked seating and out via ceiling mounted openings so that the screening room was flushed entirely circa 6 times per hour. The measurement instruments (PTR-ToFMS and the CO 2 detector, see below for details) were located outside the screening room (to avoid possible noise disturbance), in a technical room that contained the outgoing air vents (75 × 75 cm square stainless steel) and associated control systems for all auditoriums, see Fig. 4c. An inlet was inserted into the midpoint of the exit flow vent and a 10 L/min flow was drawn through ¼” OD (0.625 cm) Teflon line continuously, see Fig. 4d. The films viewed and the number of screenings are given in Table 1a. This is a study of ambient air and the chemical changes within it caused by entirely anonymous groups of people in a public space. No personal data concerning the cinemagoers was collected, no individuals identified, only the number of people present were recorded by way of the ticket sales.

Figure 4 (a) The Cinestar Cinema in Mainz, Germany, (b) The 230 seat capacity cinema audioreum, (c) the air ventilation system, (d) insertion of the Teflon inlet into the 75 × 75 cm ventilation system. (a,b) are reproduced with permission from Cinestar. Full size image

Proton Transfer Reaction Time of Flight Mass Spectrometer

Volatile Organic Compounds (VOC) were measured using a commercial PTR-ToFMS (Proton Transfer Reaction Time of Flight Mass Spectrometer, PTR-ToF-MS-8000, Ionicon Analytik GmbH, Innsbruck, Austria)38,39. The measurement technique is based on the low pressure (ca. 2 mbar) protonation of molecules with a proton affinity higher than water by H 3 O+ ions (691 kJ mol−1) that are generated in a hollow cathode discharge chamber flushed with water vapour. All protonated molecular ions are accelerated by an electrical field to the same kinetic energy such that the resultant velocity of the ions depends on the mass-to-charge ratio. Hence, the time-of-flight is used to measure the velocity, from which the mass-to-charge ratio can be determined. The TOF was configured in the standard V mode with a mass resolution of approximately 3700 m/∆m. Mass spectra were collected ranging from m/z 10–400 with a TOF acquisition sampling time per channel of 0.1 ns. The instrument was operated with a drift pressure of 2.20 hPa (E/N 137 Td) and a drift voltage of 600 V. For mass calibration, 1,3,5-trichlorobenzene was used as an internal standard by permeating 1,3,5-trichlorobenzene into a 1 mm section of 1/8” (1.58 mm) Teflon tubing used in the inlet system. Data post-processing and analysis was performed by using the program “PTR-TOF DATA ANALYZER”, which is described elsewhere40. The PTR-ToFMS was calibrated with a commercial pressurized gas standard mixture (Apel-Riemer Environmental Inc., Broomfield, USA) of known mixing ratio. The overall uncertainty was 15%. The calculated detection limit (3σ of the noise) of identified masses was between15 ppt and 155 ppt. Signals were normalized to H 3 O+ ions and the first water cluster H 3 O(H 2 O)+ by means of the following formula:

here [R+]ncps is the normalized counts per second, [R+] is the reagent ion, P the pressure, T the temperature, [m21] the counts per second of the O18 isotope of H 3 O+ and [m39] the counts per second of the 18O isotope of the first water cluster of the primary ion. The signal is normalized to a temperature of 298.15 K and a pressure of 2 mbar. The humidity dependence of the PTR-ToF-MS sensitivity was tested for a suite of compounds including key breath species such as isoprene and acetone shown in Fig. 2. The sensitivity was weak, varying in the order of 3% for the ambient conditions in the cinema and therefore we can exclude humidity dependent variations in sensitivity as the cause of the peaks shown.

Carbon Dioxide (CO 2 ) measurement

CO 2 was measured at 1 Hz using a commercially available Li-COR Li-7000 system. The Li-7000 monitor was calibrated using a standard containing 509 ± 10 ppmv of CO 2 ppmv (Air Liquide, Germany) before and during the campaign. The instrument specifications state that the response is linear up to 3000 ppmv. Post campaign the linearity of the response was confirmed to 3400 ppmv using a second standard gas (10% CO 2 , Air Liquide, Germany).

Film scene annotation

In order to assess the data for relationships between film scene content and trace gas behavior it was necessary to annotate the film scene content at high time resolution, from a set of preselected labels. Although several approaches to film scene annotation have been reported, including scene change frequency and both audio and visual cues40,41,42,43, as yet no standardized procedure exists. Suitable independently derived time resolved annotations were also not available from film censor boards nor from the subsequently published film DVDs. Instead, ten volunteers individually viewed the films and allocated descriptor annotations as a function of the film duration using a custom made interface. Each film was labelled at least five separate times. Three different types of scene labels were used. The first set was general in nature and described the film genre using terms from the Internet Movie Database (IMDb). These included terms such as “comedy”, “suspense” or “romantic.” The second set was more specific and referred directly to the scene content such as “chase”, “laughter” or “kiss”, “house pet” or “injury”. These terms were kept deliberately objective to minimize potential labelling differences between individuals caused by personal perception. Finally, we have adopted an emotional assessment scheme that has been previously used by psychologists44. It consists of two separate five point scales, one ranging from happy to sad and the other from excited to calm. The labels produced by the individual volunteers were then averaged and used only when two thirds of the individuals agreed. The labels were created to match the datapoint frequency (1 every 30 seconds). A full list of scene labels is in Table 1b,c and a comprehensive description of all data mining approaches applied to the dataset given by Wicker et al.33.

Data Mining