Human beings emit many volatile organic compounds (VOCs) of both endogenous (internally produced) and exogenous (external source) origin. Here we present realworld emission rates of volatile organic compounds from cinema audiences people) as a function of time in multiple screenings of three films. The cinema location and film selection allowed high-frequency measurement of human-emitted VOCs within a room flushed at a known rate so that emissions rates could be calculated for both adults and children. Gas-phase emission rates are analyzed as a function of time of day, variability during the film, and age of viewer. The average emission rates of CO 2 , acetone, and isoprene were lower (by a factor of ~1.2-1.4) for children under twelve compared to adults while for acetaldehyde emission rates were equivalent.Molecules influenced by exogenous sources such as decamethylcyclopentasiloxanes and methanol tended to decrease over the course of day and then rise for late evening screenings. These results represent average emission rates of people under real-world conditions and can be used in indoor air quality assessments and building design.Averaging over a large number of people generates emission rates that are less susceptible to individual behaviors. K E Y W O R D Scrowd breath, emission rate, indoor air quality, movie theatre, proton transfer reaction time-offlight mass spectrometry, volatile organic compounds (1.2-1880 ppb), isoprene (12-580 ppb), ethanol (13-1000 ppb), and methanol (160-2000 ppb (8300) under real-world conditions so as to include both endogenous and exogenous species. The aim is to provide a representative dataset of typical city dwelling human emission rates that can be used by architects, indoor air quality specialists, and medical researchers. Groups of people (50-238 at a time) were measured in a cinema which served as a convenient enclosed space that was ventilated at a known rate while the audience remained seated. By characterizing the human emission rates of VOCs and CO 2 in the real world, we may put other indoor sources into context and gauge the potential for indoor chemical reactions. | INTRODUCTIONHere, we present emission rates for numerous VOCs from seated | MATERIALS AND METHODS | Cinema/movie theatreThe measurements were made from screening room 2 in the Cinestar Cinema Complex in Mainz between December 15, 2015 and January 15, 2016. Within this time period, three films were screened: "Star Wars:The Force Awakens" and two German films "I′m off then" (German title "Ich bin dann mal weg") and "Help, I′ve shrunk my teacher" (German title "Hilfe, ich habe meine Lehrerin geschrumpft"). According to the "International Movie Database," 32 the "Star Wars" film falls under the genre "Action," "Adventure," and "Fantasy" whereas the other two films were "Comedy" films. The third film was additionally categorized under "Family," indicating that it was targeted at younger audiences. StarWars was classified as suitable for viewing by people of 12 and above, while the other two fil...
Abstract. Hydroxyl (OH) radical reactivity (k OH ) has been measured for 18 years with different measurement techniques. In order to compare the performances of instruments deployed in the field, two campaigns were conducted performing experiments in the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich in October 2015 and April 2016. Chemical conditions were chosen either to be representative of the atmosphere or to test potential limitations of instruments. All types of instruments that are currently used for atmospheric measurements were used in one of the two campaigns. The results of these campaigns demonstrate that OH reactivity can be accurately measured for a wide range of atmospherically relevant chemical conditions (e.g. water vapour, nitrogen oxides, various organic compounds) by all instruments. The precision of the measurements (limit of detection < 1 s −1 at a time resolution of 30 s to a few minutes) is higher for instruments directly detecting hydroxyl radicals, whereas the indirect comparative reactivPublished by Copernicus Publications on behalf of the European Geosciences Union. H. Fuchs et al.: OH reactivity comparison in SAPHIRity method (CRM) has a higher limit of detection of 2 s −1 at a time resolution of 10 to 15 min. The performances of the instruments were systematically tested by stepwise increasing, for example, the concentrations of carbon monoxide (CO), water vapour or nitric oxide (NO). In further experiments, mixtures of organic reactants were injected into the chamber to simulate urban and forested environments. Overall, the results show that the instruments are capable of measuring OH reactivity in the presence of CO, alkanes, alkenes and aromatic compounds. The transmission efficiency in Teflon inlet lines could have introduced systematic errors in measurements for low-volatile organic compounds in some instruments. CRM instruments exhibited a larger scatter in the data compared to the other instruments. The largest differences to reference measurements or to calculated reactivity were observed by CRM instruments in the presence of terpenes and oxygenated organic compounds (mixing ratio of OH reactants were up to 10 ppbv). In some of these experiments, only a small fraction of the reactivity is detected. The accuracy of CRM measurements is most likely limited by the corrections that need to be applied to account for known effects of, for example, deviations from pseudo first-order conditions, nitrogen oxides or water vapour on the measurement. Methods used to derive these corrections vary among the different CRM instruments. Measurements taken with a flowtube instrument combined with the direct detection of OH by chemical ionisation mass spectrometry (CIMS) show limitations in cases of high reactivity and high NO concentrations but were accurate for low reactivity (< 15 s −1 ) and low NO (< 5 ppbv) conditions.
Abstract. The Arabian Peninsula is characterized by high and increasing levels of photochemical air pollution. Strong solar irradiation, high temperatures and large anthropogenic emissions of reactive trace gases result in intense photochemical activity, especially during the summer months. However, air chemistry measurements in the region are scarce. In order to assess regional pollution sources and oxidation rates, the first ship-based direct measurements of total OH reactivity were performed in summer 2017 from a vessel traveling around the peninsula during the AQABA (Air Quality and Climate Change in the Arabian Basin) campaign. Total OH reactivity is the total loss frequency of OH radicals due to all reactive compounds present in air and defines the local lifetime of OH, the most important oxidant in the troposphere. During the AQABA campaign, the total OH reactivity ranged from below the detection limit (5.4 s−1) over the northwestern Indian Ocean (Arabian Sea) to a maximum of 32.8±9.6 s−1 over the Arabian Gulf (also known as Persian Gulf) when air originated from large petroleum extraction/processing facilities in Iraq and Kuwait. In the polluted marine regions, OH reactivity was broadly comparable to highly populated urban centers in intensity and composition. The permanent influence of heavy maritime traffic over the seaways of the Red Sea, Gulf of Aden and Gulf of Oman resulted in median OH sinks of 7.9–8.5 s−1. Due to the rapid oxidation of direct volatile organic compound (VOC) emissions, oxygenated volatile organic compounds (OVOCs) were observed to be the main contributor to OH reactivity around the Arabian Peninsula (9 %–35 % by region). Over the Arabian Gulf, alkanes and alkenes from the petroleum extraction and processing industry were an important OH sink with ∼9 % of total OH reactivity each, whereas NOx and aromatic hydrocarbons (∼10 % each) played a larger role in the Suez Canal, which is influenced more by ship traffic and urban emissions. We investigated the number and identity of chemical species necessary to explain the total OH sink. Taking into account ∼100 individually measured chemical species, the observed total OH reactivity can typically be accounted for within the measurement uncertainty (50 %), with 10 dominant trace gases accounting for 20 %–39 % of regional total OH reactivity. The chemical regimes causing the intense ozone pollution around the Arabian Peninsula were investigated using total OH reactivity measurements. Ozone vs. OH reactivity relationships were found to be a useful tool for differentiating between ozone titration in fresh emissions and photochemically aged air masses. Our results show that the ratio of NOx- and VOC-attributed OH reactivity was favorable for ozone formation almost all around the Arabian Peninsula, which is due to NOx and VOCs from ship exhausts and, often, oil/gas production. Therewith, total OH reactivity measurements help to elucidate the chemical processes underlying the extreme tropospheric ozone concentrations observed in summer over the Arabian Basin.
We investigated the conductance of C 60 molecules using mechanically controllable break-junction electrodes at 10 K in UHV. The molecules are evaporated in situ. With this method, we obtain clean and low-resistance contacts. From the analysis of conductance histograms and differential-conductance ͑dI / dV͒ traces, we deduce the preferred conductance value of a single C 60 molecule between gold electrodes to be close to 0.1 G 0 . The presence of C 60 is evidenced by features in the derivative of the dI / dV at energies close to the molecular vibration energies. The characteristics of the molecules disappear upon cold working of the junctions. DOI: 10.1103/PhysRevB.76.125432 Over the last years, much progress has been achieved in the understanding of the electronic transport through single molecules. Since the seminal experiment by Joachim et al. 1 in which a C 60 molecule was contacted by a scanningtunneling microscope tip, the fullerenes have become benchmark systems for the development of new measurement schemes for molecular electronics applications. Much theoretical work has been performed on different metal-C 60 systems including the noble metals 2 and aluminum. 3 It has been measured that C 60 between gold electrodes would form ionic contacts, giving rise to high conductances. 4,5 Due to its high symmetry, only a few different contact geometries have to be explored although the molecule bears manifold possible functionality including the possibility of endodoping by magnetic 6,7 or other ions. 8 Most of the single-molecule transport experiments performed so far can be categorized into two groups: The first set of experiments is characterized by rather high resistance contacts allowing for the investigation of Coulomb blockade ͑CB͒ and molecular level spectroscopy by inelastic electron tunneling spectroscopy. These devices can be fabricated by different techniques including scanningtunneling microscopy ͑STM͒ and spectroscopy, 1 electromigrated electrode structures, 9,10 and mechanically controllable break junctions ͑MCBJs͒.11 Among those, STM provides the largest variability in the combination of metals and molecules, to tune the contact after its formation, to reestablish a new contact after it has been broken, and to image the configuration of the environment. With electromigrated electrodes, very stable devices are achieved but without any possibility to tune the coupling after the contact has been established and with usually very low yield. The MCBJ technique interpolates between these two extremes. It combines tunability of the contacts with high mechanical stability, enabling measurements over several hours on the same contact configuration at low temperatures and the application of external fields.For the study of CB, oxide or other contamination layers between electrodes and molecules might be helpful for ensuring the weak coupling which is necessary for considering the molecular systems as independent from the metal electrodes. However, for the application of single-molecule contacts in ele...
Dissociative electron attachment to dialanine and alanine anhydride has been studied in the gas phase utilizing a double focusing two sector field mass spectrometer. We show that low-energy electrons (i.e., electrons with kinetic energies from near zero up to 13 eV) attach to these molecules and subsequently dissociate to form a number of anionic fragments. Anion efficiency curves are recorded for the most abundant anions by measuring the ion yield as a function of the incident electron energy. The present experiments show that as for single amino acids (M), e.g., glycine, alanine, valine, and proline, the dehydrogenated closed shell anion (M-H) − is the most dominant reaction product. The interpretation of the experiments is aided by quantum chemical calculations based on density functional theory, by which the electrostatic potential and molecular orbitals are calculated and the initial electron attachment process prior to dissociation is investigated.
Abstract. Methane sulfonamide (MSAM), CH3S(O)2NH2, was recently detected for the first time in ambient air over the Red Sea and the Gulf of Aden where peak mixing ratios of ≈60 pptv were recorded. Prior to this study the rate constant for its reaction with the OH radical and the products thereby formed were unknown, precluding assessment of its role in the atmosphere. We have studied the OH-initiated photo-oxidation of MSAM in air (298 K, 700 Torr total pressure) in a photochemical reactor using in situ detection of MSAM and its products by Fourier transform infrared (FTIR) absorption spectroscopy. The relative rate technique, using three different reference compounds, was used to derive a rate coefficient of (1.4±0.3)×10-13cm3molec.-1s-1. The main end products of the photo-oxidation observed by FTIR were CO2, CO, SO2, and HNO3 with molar yields of (0.73±0.11), (0.28±0.04), (0.96±0.15), and (0.62±0.09), respectively. N2O and HC(O)OH were also observed in smaller yields of (0.09±0.02) and (0.03±0.01). Both the low rate coefficient and the products formed are consistent with hydrogen abstraction from the −CH3 group as the dominant initial step. Based on our results MSAM has an atmospheric lifetime with respect to loss by reaction with OH of about 80 d.
Abstract. Volatile organic compounds (VOCs) were measured around the Arabian Peninsula using a research vessel during the AQABA campaign (Air Quality and Climate Change in the Arabian Basin) from June to August 2017. In this study we examine carbonyl compounds, measured by a proton transfer reaction mass spectrometer (PTR-ToF-MS), and present both a regional concentration distribution and a budget assessment for these key atmospheric species. Among the aliphatic carbonyls, acetone had the highest mixing ratios in most of the regions traversed, varying from 0.43 ppb over the Arabian Sea to 4.5 ppb over the Arabian Gulf, followed by formaldehyde (measured by a Hantzsch monitor, 0.82 ppb over the Arabian Sea and 3.8 ppb over the Arabian Gulf) and acetaldehyde (0.13 ppb over the Arabian Sea and 1.7 ppb over the Arabian Gulf). Unsaturated carbonyls (C4–C9) varied from 10 to 700 ppt during the campaign and followed similar regional mixing ratio dependence to aliphatic carbonyls, which were identified as oxidation products of cycloalkanes over polluted areas. We compared the measurements of acetaldehyde, acetone, and methyl ethyl ketone to global chemistry-transport model (ECHAM5/MESSy Atmospheric Chemistry – EMAC) results. A significant discrepancy was found for acetaldehyde, with the model underestimating the measured acetaldehyde mixing ratio by up to an order of magnitude. Implementing a photolytically driven marine source of acetaldehyde significantly improved the agreement between measurements and model, particularly over the remote regions (e.g. Arabian Sea). However, the newly introduced acetaldehyde source was still insufficient to describe the observations over the most polluted regions (Arabian Gulf and Suez), where model underestimation of primary emissions and biomass burning events are possible reasons.
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