<p>Between April and June 2013 fluxes of volatile organic compounds (VOCs) were measured in a Scots pine and Norway spruce forest using the eddy covariance (EC) method with a proton transfer reaction time of flight (PTR-TOF) mass spectrometer. The observations were performed above a boreal forest at the SMEAR II site in Southern Finland. We found a total of 25 different compounds with exchange and investigated their seasonal variations from spring to summer. The majority of the net VOC flux was comprised of methanol, monoterpenes, acetone and butene. The VOC emissions followed a seasonal trend, the released amount increased from spring to summer. Only a three compounds were emitted in April while in June emissions of some 19 VOCs were observed. During the measurements in April, the emissions were dominated by butene, while in May and June methanol was the most emitted compound. The main source of methanol is likely the growth of new biomass. During a 21-day period in June, the net VOC flux was 2.3&thinsp;nmol&thinsp;m&minus;2&thinsp;s&minus;1. This is on the lower end of PTR-TOF flux measurements from other ecosystems, which range from 2 to 10&thinsp;nmol&thinsp;m&minus;2&thinsp;s&minus;1. The EC flux results were compared with surface layer profile measurements, an indirect method using a proton transfer reaction quadrupole mass spectrometer, which is permanently installed at the SMEAR II site was used. For most of the compounds the fluxes, measured with the two different methods, agreed well.</p>

<p>To survey landscape-scale fluxes of biogenic gases, a 100 m Teflon tube was attached to a tethered balloon as a sampling inlet for a fast response Proton Transfer Reaction Mass Spectrometer (PTRMS). Along with meteorological instruments deployed on the tethered balloon and at 3 m and outputs from a regional weather model, these observations were used to estimate landscape scale biogenic volatile organic compound fluxes with two micrometeorological techniques: mixed layer variance and surface layer gradients. This highly mobile sampling system was deployed at four field sites near Barcelona to estimate landscape-scale BVOC emission factors in a relatively short period (3 weeks). The two micrometeorological techniques agreed within the uncertainty of the flux measurements at all four sites even though the locations had considerable heterogeneity in species distribution and complex terrain. The observed fluxes were significantly different than emissions predicted with an emission model using site-specific emission factors and land-cover characteristics. Considering the wide range in reported BVOC emission factors of VOCs for individual vegetation species (more than an order of magnitude), this flux estimation technique is useful for constraining BVOC emission factors used as model inputs.</p>

<p>Fossil fuel-powered vehicles emit significant particulate matter, for example, black carbon and primary organic aerosol, and produce secondary organic aerosol. Here we quantify secondary organic aerosol production from two-stroke scooters. Cars and trucks, particularly diesel vehicles, are thought to be the main vehicular pollution sources. This needs re-thinking, as we show that elevated particulate matter levels can be a consequence of &lsquo;asymmetric pollution&rsquo; from two-stroke scooters, vehicles that constitute a small fraction of the fleet, but can dominate urban vehicular pollution through organic aerosol and aromatic emission factors up to thousands of times higher than from other vehicle classes. Further, we demonstrate that oxidation processes producing secondary organic aerosol from vehicle exhaust also form potentially toxic &lsquo;reactive oxygen species&rsquo;.</p>

<p>Abstract Following up the first introduction of an advanced proton-transfer-reaction mass spectrometry (PTR-MS) instrument in 2012, which is capable of utilizing H3O+, NO+, O2+, and Kr+, respectively, for chemical ionization and subsequent detection of a broad variety of compound classes, here we present calculations of the best suitable mixing ratios between the sample and buffer gas in Kr+ mode, as well as two possible applications of such an instrument in indoor air analysis and engine exhaust studies. Due to secondary reactions in the drift tube the admixing of a buffer gas with a higher recombination energy than Kr+ is inevitable. The calculations show that though a dilution ratio of 1:40 (sample : buffer gas) results in the highest sensitivity, for accurate substance quantification a dilution ratio of at least 1:500 is necessary. By applying this theoretical knowledge to two practical examples, we find that the quantification of CH4, CO, O2, and CO2, respectively, is well within the range of the expected concentrations. We conclude that such an instrument can be of utmost benefit for researchers working for example in environmental research, because in H3O+ mode volatile organic compounds can be quantified with very high sensitivity and low detection limits and by means of switching the reagent ions to Kr+ additional instrumentation for quantification of (inorganic) pollutants becomes virtually obsolete.</p>

Most flowering plants depend on animal vectors for pollination and seed dispersal. Differential pollinator preferences lead to premating isolation and thus reduced gene flow between interbreeding plant populations [1, 2, 3 and 4]. Sets of floral traits, adapted to attract specific pollinator guilds, are called pollination syndromes [5]. Shifts in pollination syndromes have occurred surprisingly frequently [6], considering that they must involve coordinated changes in multiple genes affecting multiple floral traits. Although the identification of individual genes specifying single pollination syndrome traits is in progress in many species, little is known about the genetic architecture of coadapted pollination syndrome traits and how they are embedded within the genome [7]. Here we describe the tight genetic linkage of loci specifying five major pollination syndrome traits in the genus Petunia: visible color, UV absorption, floral scent production, pistil length, and stamen length. Comparison with other Solanaceae indicates that, in P. exserta and P. axillaris, loci specifying these floral traits have specifically become clustered into a multifunctional “speciation island” [ 8 and 9]. Such an arrangement promotes linkage disequilibrium and avoids the dissolution of pollination syndromes by recombination. We suggest that tight genetic linkage provides a mechanism for rapid switches between distinct pollination syndromes in response to changes in pollinator availabilities.

<p>Different household insecticide applications via two electric vaporizers emitting transfluthrin were realized in a full-scale experimental room under controlled air exchange rate conditions. On-line high-time resolved measurements of the gas-phase concentrations of the active substance during and immediately after the spreading periods were performed with a High Sensitivity Proton-Transfer-Reaction Mass Spectrometer (HS-PTR-MS). Experimental and modelled data from the ConsExpo 4.0 software were also compared to evaluate the sources of differences. Different application scenarios were also compared. Averaged inhaled concentrations over 1h, 1week, and 5months were estimated to be 8.3, 1.8, and 1.8μg.m(-3), respectively. Corresponding margins of exposures range from 1000 to 10,000, claiming for the absence of effect. Dermal and dust ingestion pathways, although roughly estimated, seems being non-negligible. This claims for a more in-depth integrated risk assessment.</p>

This study investigates time-dependent aroma changes in human milk after intake of an odorant-containing pharmaceutical preparation by correlating sensory evaluation with quantitative results.Human milk donors ingested 100 mg of encapsulated 1,8-cineole. 21 milk samples from 12 participants underwent sensory analysis, of which 14 samples were quantified by stable isotope dilution assay (SIDA) analysis. Furthermore, several consecutive breast milk and exhaled breath gas samples from one volunteer after intake of 1,8-cineole were analysed by proton-transfer-reaction mass spectrometry (PTR-MS) and sensory evaluation on three separate days.The emergence of the characteristic eucalyptus-like odour of 1,8-cineole in exhaled breath after capsule ingestion coincided with its transfer into milk; its presence in breath was therefore used to indicate the time at which milk should be expressed for gathering samples. Odorant transfer could not be confirmed by sensory analysis in 7 of the 21 milk samples, most likely due to disadvantageous timing of milk expression. The other 14 samples exhibited a distinct eucalyptus-like odour. Quantitative results matched these observations with <20 ?g/kg 1,8-cineole in the odourless samples and 70 to an estimated 2090 ?g/kg 1,8-cineole in the other samples.Transfer of 1,8-cineole into human milk after oral intake is time dependent and exhibits large inter and intra-individual differences.

The release of volatile organic compounds (VOCs) into the mouth cavity is an integral part of the way flavor is perceived. An in vitro model mouth with an artificial tongue was developed to measure the dynamic release of VOCs from liquid model systems [e.g., aqueous solution, oil, and oil-in-water (O/W) emulsions] under oral conditions. The release of seven selected VOCs was affected by the different polarity and vapor pressure of the compounds and their affinity to the liquid system media. Different tongue pressure patterns were applied to the liquid systems, and the release of VOCs was monitored in real time using proton transfer reaction-mass spectrometry. The release was significantly more intense for longer tongue pressure duration and was influenced by the tongue altering the sample surface area and the distribution of the VOCs. The role of saliva (artificial versus human) and the sample temperature had a significant effect on VOC release. Saliva containing mucin and a higher sample temperature enhanced the release.

Hydroxyl radicals play a central role in the troposphere as they control the lifetime of many trace gases. Measurement of OH reactivity (OH loss rate) is important to better constrain the OH budget and also to evaluate the completeness of measured VOC budget. Total atmospheric OH reactivity was measured for the first time in an European Megacity: Paris and its surrounding areas with 12 million inhabitants, during the MEGAPOLI winter campaign 2010. The method deployed was the Comparative Reactivity Method (CRM). The measured dataset contains both measured and calculated OH reactivity from CO, NOx and VOCs measured via PTR-MS, GC-FID and GC-MS instruments. The reactivities observed in Paris covered a range from 10 s−1 to 130 s−1, indicating a large loading of chemical reactants. The present study showed that, when clean marine air masses influenced Paris, the purely local OH reactivity (20 s−1) is well explained by the measured species. Nevertheless, when there is a continental import of air masses, high levels of OH reactivity were obtained (120–130 s−1) and the missing OH reactivity measured in this case jumped to 75%. Using covariations of the missing OH reactivity to secondary inorganic species in fine aerosols, we suggest that the missing OH reactants were most likely highly oxidized compounds issued from photochemically processed air masses of anthropogenic origin.

Root herbivores are notoriously difficult to study, as they feed hidden in the soil. However, root herbivores may be traced by analyzing specific volatile organic compounds (VOCs) that are produced by damaged roots. These VOCs not only support parasitoids in the localization of their host, but also may help scientists study belowground plant-herbivore interactions. Herbivore-induced VOCs are usually analyzed by gas-chromatography mass spectrometry (GC-MS), but with this off-line method, the gases of interest need to be preconcentrated, and destructive sampling is required to assess the level of damage to the roots. In contrast to this, proton-transfer-reaction mass spectrometry (PTR-MS) is a very sensitive on-line, non-invasive method. PTR-MS already has been successfully applied to analyze VOCs produced by aboveground (infested) plant parts. In this review, we provide a brief overview of PTR-MS and illustrate how this technology can be applied to detect specific root-herbivore induced VOCs from Brassica plants. We also specify the advantages and disadvantages of PTR-MS analyses and new technological developments to overcome their limitations.

Thermal desorption extraction proton transfer reaction mass spectrometer (TDE-PTR-MS) has been exploited to provide rapid determination of residual solvent and sterilant like cyclohexanone (CHX) and ethylene oxide (EO) in disposable medical devices. Two novel methods are proposed for the quantification of residual chemicals in the polyvinyl chloride infusion sets with our homemade PTR-MS. In the first method, EO residue in the solid infusion sets (y, mgset(-1)) is derived through the determination of EO gas concentration within its packaging bag (x, ppm) according to the correlative equation of y=0.00262x. In the second one, residual EO and CHX in the solid infusion sets are determined through a time integral of their respective mass emission rates. The validity of the proposed methods is demonstrated by comparison with the experimental results from the exhaustive extraction method. Due to fast response, absolute concentration determination and high sensitivity, the TDE-PTR-MS is suggested to be a powerful tool for the quality inspection of disposable medical devices including the quantitative determination of residual solvent and sterilant like CHX and EO.

Volatile fingerprints of 30 cumin cheese samples of artisanal farmers' cheese of Leiden with EU Protected Designation of Origin (PDO) and 29 cumin cheese samples of varying commercial Dutch brands without PDO protection were used to develop authentication models. The headspace concentrations of the volatiles, as measured with high sensitivity proton-transfer mass spectrometry, were subsequently subjected to partial least-squares discriminant analysis (PLS-DA). Farmers' cheese of Leiden showed a distinct volatile profile with 27 and 9 out of the 60 predominant ions showing respectively significantly higher and lower concentrations in the headspace of the cheese in comparison to the other cumin cheeses. The PLS-DA prediction models developed classified in cross-validation 96% of the samples of PDO protected, artisanal farmers' cheese of Leiden correctly, against 100% of commercial cumin cheese samples. The characteristic volatile compounds were tentatively identified by PTR-time-of-flight-MS. A consumer test indicated differences in appreciation, overall flavor intensity, creaminess, and firmness between the two cheese groups. The consumers' appreciation of the cumin cheese tested was not influenced by the presence of a name label or PDO trademark.

Proton transfer reaction mass spectrometry (PTR-MS) is a technique for online measurements of atmospheric concentrations, or volume mixing ratios, of volatile organic compounds (VOCs). This paper gives a detailed description of our measurement, calibration, and volume mixing ratio calculation methods, which have been designed for long-term stand-alone field measurements by PTR-MS. The PTR-MS instrument has to be calibrated regularly with a gas standard to ensure the accuracy needed in atmospheric VOC measurements. We introduce a novel method for determining an instrument specific relative transmission curve using information obtained from a calibration. This curve enables consistent mixing ratio calculation for VOCs not present in a calibration gas standard. Our method proved to be practical, systematic, and sensitive enough to capture changes in the transmission over time. We also propose a new approach to considering the abundance of H3O+H2O ions in mixing ratio calculation. The approach takes into account the difference in the transmission efficiencies for H3O+ and H3O+H2O ions. To illustrate the functionality of our measurement, calibration, and calculation methods, we present a one-month period of ambient mixing ratio data measured in a boreal forest ecosystem at the SMEAR II station in southern Finland. During the measurement period 27 March–26 April 2007, the hourly averages of the mixing ratios were 0.051–0.57 ppbv for formaldehyde, 0.19–3.1 ppbv for methanol, 0.038–0.39 ppbv for benzene, and 0.020–1.3 ppbv for monoterpenes. The detection limits for the hourly averages were 0.020, 0.060, 0.0036, and 0.0092 ppbv, respectively.

<p>Airborne and ground-based mixing ratio and flux measurements using eddy covariance (EC) and for the first time the mixed layer gradient (MLG) and mixed layer variance (MLV) techniques are used to assess the impact of isoprene and monoterpene emissions on atmospheric chemistry in the Amazon basin. Average noon isoprene (7.8 &plusmn; 2.3 mg/m2/h) and monoterpene fluxes (1.2 &plusmn; 0.5 mg/m2/h) compared well between ground and airborne measurements and are higher than fluxes estimated in this region during other seasons. The biogenic emission model, Model of Emissions of Gases and Aerosols from Nature (MEGAN), estimates fluxes that are within the model and measurement uncertainty and can describe the large observed variations associated with land-use change in the region north-west of Manaus. Isoprene and monoterpenes accounted for &sim;75% of the total OH reactivity in this region and are important volatile organic compounds (VOCs) for modeling atmospheric chemistry in Amazonia. The presence of fair weather clouds (cumulus humilis) had an important impact on the vertical distribution and chemistry of VOCs through the planetary boundary layer (PBL), the cloud layer, and the free troposphere (FT). Entrainment velocities between 10:00 and 11:30 local time (LT) are calculated to be on the order of 8&ndash;10 cm/s. The ratio of methyl-vinyl-ketone (MVK) and methacrolein (MAC) (unique oxidation products of isoprene chemistry) with respect to isoprene showed a pronounced increase in the cloud layer due to entrainment and an increased oxidative capacity in broken cloud decks. A decrease of the ratio in the lower free troposphere suggests cloud venting through activated clouds. OH modeled in the planetary boundary layer using a photochemical box model is much lower than OH calculated from a mixed layer budget approach. An ambient reactive sesquiterpene mixing ratio of 1% of isoprene would be sufficient to explain most of this discrepancy. Increased OH production due to increased photolysis in the cloud layer balances the low OH values modeled for the planetary boundary layer. The intensity of segregation (Is) of isoprene and OH, defined as a relative reduction of the reaction rate constant due to incomplete mixing, is found to be significant: up to 39 &plusmn; 7% in the &sim;800-m-deep cloud layer. The effective reaction rate between isoprene and OH can therefore vary significantly in certain parts of the lower atmosphere.</p>

Volatile Organic Compound (VOC) emissions from fires in tropical forest fuels were quantified using Proton-Transfer-Reaction Mass Spectrometry (PTRMS), Fourier Transform Infrared Spectroscopy (FTIR) and gas chromatography (GC) coupled to PTRMS (GC-PTR-MS). We investigated VOC emissions from 19 controlled laboratory fires at the USFS (United States Forest Service) Fire Sciences Laboratory and 16 fires during an intensive airborne field campaign during the peak of the burning season in Brazil in 2004. The VOC emissions were dominated by oxygenated VOCs (OVOC) (OVOC/NMHC  4:1, NMHC: non-methane hydrocarbons) The specificity of the PTR-MS instrument, which measures the mass to charge ratio of VOCs ionized by H3O+ ions, was validated by gas chromatography and by intercomparing in-situ measurements with those obtained from an open path FTIR instrument. Emission ratios for methyl vinyl ketone, methacrolein, crotonaldehyde, acrylonitrile and pyrrole were measured in the field for the first time. Our measurements show a higher contribution of OVOCs than previously assumed for modeling purposes. Comparison of fresh (<15 min) and aged (>1 h–1 d) smoke suggests altered emission ratios due to gas phase chemistry for acetone but not for acetaldehyde and methanol. Emission ratios for numerous, important, reactive VOCs with respect to acetonitrile (a biomass burning tracer) are presented.

Numerical modelling is an efficient tool to investigate the role of chemical degradation of biogenic volatile organic compounds (BVOC) and the effect of dynamical processes on BVOC and product mixing ratios within and above forest canopies. The present study shows an application of the coupled canopy-chemistry model CACHE to a Norway spruce forest at the Waldstein (Fichtelgebirge, Germany). Simulated courses of temperature, trace gas mixing ratios, and fluxes are compared with measurements taken during the BEWA2000 field campaigns. The model permits the interpretation of the observed diurnal course of ozone and VOC by investigating the role of turbulent exchange, chemical formation and degradation, emission, and deposition during the course of the day. The simulation results show that BVOC fluxes into the atmosphere are 10–15% lower than the emission fluxes on branch basis due to chemical BVOC degradation within the canopy. BVOC degradation by the NO3 radical was found to occur in the lower part of the canopy also during daytime. Furthermore, the simulations strongly indicate that further research is still necessary concerning the emission and deposition of aldehydes and ketones.

In this study, we investigated the prompt release of acetaldehyde and other oxygenated volatile organic compounds (VOCs) from leaves of Grey poplar [Populus x canescens (Aiton) Smith] following light-dark transitions. Mass scans utilizing the extremely fast and sensitive proton transfer reaction-mass spectrometry technique revealed the following temporal pattern after light-dark transitions: hexenal was emitted first, followed by acetaldehyde and other C6-VOCs. Under anoxic conditions, acetaldehyde was the only compound released after switching off the light. This clearly indicated that hexenal and other C6-VOCs were released from the lipoxygenase reaction taking place during light-dark transitions under aerobic conditions. Experiments with enzyme inhibitors that artificially increased cytosolic pyruvate demonstrated that the acetaldehyde burst after light-dark transition could not be explained by the recently suggested pyruvate overflow mechanism. The simulation of light fleck situations in the canopy by exposing leaves to alternating light-dark and dark-light transitions or fast changes from high to low photosynthetic photon flux density showed that this process is of minor importance for acetaldehyde emission into the Earth's atmosphere.

Real time monitoring of volatile organic compounds (VOCs) using a Proton-Transfer Reaction Mass Spectrometer was performed at the Mauna Loa Baseline Station (19.54N, 155.58W) in March/April 2001 (March 23, 2001–April 17, 2001). Mixing ratios for methanol, acetone, acetonitrile, isoprene and methyl vinyl ketone (MVK) plus methacrolein (MACR) ranged between 0.2 and 1.8, 0.2 and 1, 0.07 and 0.2, <0.02 and 0.3, and <0.02 and 0.5 ppbv, respectively. Biomass burning plumes transported from South-East Asia and the Indian Subcontinent across the Pacific influenced part of the measurement campaign. ΔAcetonitrile/ΔCO and Δacetone/Δacetonitrile ratios in these cases were 1.5×10−3 to 2.5×10−3 and 2–5 ppbv/ppbv, respectively. Overall Asian outflow events were not as frequent during Spring 2001 as in previous years. Methanol did not show significant correlation with CO, acetonitrile, and acetone. The abundance of acetone and CO seemed to be influenced but not dominated by biomass burning and domestic biofuel emissions.

A recently developed technique, Proton-Transfer-Reaction Mass-Spectrometry (PTR-MS), is reviewed based on applications on coffee. PTR-MS is a sensitive and fast method for on-line trace gas analysis. It consists of a specially designed chemical ionization cell, where headspace gas is continuously introduced and volatile organic compounds ionized by proton-transfer from H3O+. Protonated compounds are then mass analyzed in a quadrupole mass filter. First a description of the method will be given, with emphasis on the ionization mechanism. We then discuss a series of experiments that allow mass spectral intensities to be related to chemical compounds. Finally, two applications on coffee are discussed.