Inferring the diurnal variability of OH radical concentrations over the Amazon from BVOC measurements.

The atmospheric oxidation of biogenic volatile organic compounds (BVOC) by OH radicals over tropical rainforests impacts local particle production and the lifetime of globally distributed chemically and radiatively active gases. For the pristine Amazon rainforest during the dry season, we empirically determined the diurnal OH radical variability at the forest-atmosphere interface region between 80 and 325 m from 07:00 to 15:00 LT using BVOC measurements. A dynamic time warping approach was applied showing that median averaged mixing times between 80 to 325 m decrease from 105 to 15 min over this time period. The inferred OH concentrations show evidence for an early morning OH peak (07:00-08:00 LT) and an OH maximum (14:00 LT) reaching 2.2 (0.2, 3.8) × 106 molecules cm-3 controlled by the coupling between BVOC emission fluxes, nocturnal NOx accumulation, convective turbulence, air chemistry and photolysis rates. The results were evaluated with a turbulence resolving transport (DALES), a regional scale (WRF-Chem) and a global (EMAC) atmospheric chemistry model.

The Red Sea Deep Water is a potent source of atmospheric ethane and propane.

Non-methane hydrocarbons (NMHCs) such as ethane and propane are significant atmospheric pollutants and precursors of tropospheric ozone, while the Middle East is a global emission hotspot due to  extensive oil and gas production. Here we compare in situ hydrocarbon measurements, performed around the Arabian Peninsula, with global model simulations that include current emission inventories (EDGAR) and state-of-the-art atmospheric circulation and chemistry mechanisms (EMAC model). While measurements of high mixing ratios over the Arabian Gulf are adequately simulated, strong underprediction by the model was found over the northern Red Sea. By examining the individual sources in the model and by utilizing air mass back-trajectory investigations and Positive Matrix Factorization (PMF) analysis, we deduce that Red Sea Deep Water (RSDW) is an unexpected, potent source of atmospheric NMHCs. This overlooked underwater source is comparable with total anthropogenic emissions from entire Middle Eastern countries, and significantly impacts the regional atmospheric chemistry.

Proof of concept study: Testing human volatile organic compounds as tools for age classification of films.

Humans emit numerous volatile organic compounds (VOCs) through breath and skin. The nature and rate of these emissions are affected by various factors including emotional state. Previous measurements of VOCs and CO2 in a cinema have shown that certain chemicals are reproducibly emitted by audiences reacting to events in a particular film. Using data from films with various age classifications, we have studied the relationship between the emission of multiple VOCs and CO2 and the age classifier (0, 6, 12, and 16) with a view to developing a new chemically based and objective film classification method. We apply a random forest model built with time independent features extracted from the time series of every measured compound, and test predictive capability on subsets of all data. It was found that most compounds were not able to predict all age classifiers reliably, likely reflecting the fact that current classification is based on perceived sensibilities to many factors (e.g. incidences of violence, sex, antisocial behaviour, drug use, and bad language) rather than the visceral biological responses expressed in the data. However, promising results were found for isoprene which reliably predicted 0, 6 and 12 age classifiers for a variety of film genres and audience age groups. Therefore, isoprene emission per person might in future be a valuable aid to national classification boards, or even offer an alternative, objective, metric for rating films based on the reactions of large groups of people.

Real-world volatile organic compound emission rates from seated adults and children for use in indoor air studies.

Human beings emit many volatile organic compounds (VOCs) of both endogenous (internally produced) and exogenous (external source) origin. Here we present real-world emission rates of volatile organic compounds from cinema audiences (50-230 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 CO2 , 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.

Strong fragmentation processes driven by low energy electron attachment to various small perfluoroether molecules.

Negative ion formation in the three perfluoroethers (PFEs) diglyme (C(6)F(14)O(3)), triglyme (C(8)F(18)O(4)) and crownether (C(10)F(20)O(5)) is studied following electron attachment in the range from ∼0 to 15 eV. All three compounds show intense low energy resonances at subexcitation energies (<3 eV) decomposing into a variety of negatively charged fragments. These fragment ions are generated via dissociative electron attachment (DEA), partly originating from sequential decompositions on the metastable (µs) time scale as observed from the MIKE (metastable induced kinetic energy) scans. Only in perfluorocrownether a signal due to the non-decomposed parent anion is observed. Additional and comparatively weaker resonances are located in the energy range between ∼10 and 17 eV which preferentially decompose into lighter ions. It is suggested that specific features of perfluoropolyethers (PFPEs) relevant in applications, e.g., the strong bonding to surfaces induced by UV radiation of the substrate or degradation of PFPE films in computer hard disc drives can be explained by their pronounced sensitivity towards low energy electrons.

Dissociative electron attachment to gas-phase formamide.

Dissociative electron attachment (DEA) to gaseous formamide, HCONH(2), has been investigated in the energy range between 0 eV and 18 eV using a crossed electron/molecule beam technique. The negative ion fragments have been comprehensively monitored and assigned to molecular structures by comparison with the results for two differently deuterated derivatives, namely 1D-formamide, DCONH(2), and N,N,D-formamide, HCOND(2). The following products were observed: HCONH(-), CONH(2)(-), HCON(-), OCN(-), HCNH(-), CN(-), NH(2)(-)/O(-), NH(-), and H(-). NH(2)(-) was also separated from O(-) by using high-resolution negative ion mass spectrometry. Four resonant dissociation channels can be resolved, the strongest ones being located between 2.0 and 2.7 eV and between 6.0 and 7.0 eV. CN(-) as the most abundant fragment and HCONH(-) are the dominant products of the first of these two resonances. The most important products of the latter resonance are NH(2)(-), CN(-), H(-), CONH(2)(-), and OCN(-). It is thus found that the loss of neutral H is a site-selective process, dissociation from the N site taking place between 2.0 and 2.7 eV while dissociation from the C site occurs between 6.0 and 7.0 eV. The suitability of these reactions and thus of formamide as an agent for electron-induced surface functionalisation is discussed.

Dissociative electron attachment to pentaerythritol tetranitrate: significant fragmentation near 0 eV.

Gas phase dissociative electron attachment (DEA) measurements to pentaerythritol tetranitrate (PETN) are performed in a crossed electron-molecular beam experiment at high-energy resolution and high sensitivity. DEA is operative at very low energies close to approximately 0 eV showing unique features corresponding to a variety of fragment anions being formed. There is no evidence of the parent anion formation. The fragmentation yields are also observed for higher electron energies and are operative via several resonant features in the range of 0-12 eV. In contrast to nitroaromatic compounds, PETN decays more rapidly upon electron attachment and preferentially low-mass anions are formed. The dominant fragment ion formed through DEA is assigned to the nitrogen trioxide NO(3)(-) and represents about 80% of the total anion yield. Further intense ion signals are due to NO(2)(-) (11%) and O(-) (2.5%). The significant instability of PETN after attachment of an electron with virtually no kinetic energy confers a highly explosive nature to this compound.

Metastable anions of dinitrobenzene: resonances for electron attachment and kinetic energy release.

Attachment of free, low-energy electrons to dinitrobenzene (DNB) in the gas phase leads to DNB(-) as well as several fragment anions. DNB(-), (DNB-H)(-), (DNB-NO)(-), (DNB-2NO)(-), and (DNB-NO(2))(-) are found to undergo metastable (unimolecular) dissociation. A rich pattern of resonances in the yield of these metastable reactions versus electron energy is observed; some resonances are highly isomer-specific. Most metastable reactions are accompanied by large average kinetic energy releases (KER) that range from 0.5 to 1.32 eV, typical of complex rearrangement reactions, but (1,3-DNB-H)(-) features a resonance with a KER of only 0.06 eV for loss of NO. (1,3-DNB-NO)(-) offers a rare example of a sequential metastable reaction, namely, loss of NO followed by loss of CO to yield C(5)H(4)O(-) with a large KER of 1.32 eV. The G4(MP2) method is applied to compute adiabatic electron affinities and reaction energies for several of the observed metastable channels.