[Kuster2004] "Intercomparison of volatile organic carbon measurement techniques and data at La Porte during the TexAQS2000 Air Quality Study.",
Environ Sci Technol
, vol. 38, no. 1: Aeronomy Laboratory, National Oceanic and Atmospheric Administration, R/AL7, 325 Broadway, Boulder, Colorado 80305, USA. firstname.lastname@example.org, pp. 221–228, Jan, 2004.
The Texas Air Quality Study 2000 (TexAQS2000) investigated the photochemical production of ozone and the chemistry of related precursors and reaction products in the vicinity of Houston, TX. The colocation of four instruments for the measurement of volatile organic carbon compounds (VOCs) allowed a unique opportunity for the intercomparison of the different in-situ measuring techniques. The instruments included three gas chromatographs, each with a different type of detector, and a Proton-Transfer-Reaction Mass Spectrometer (PTR-MS) with each system designed to measure a different suite of VOCs. Correlation plots and correlation statistics are presented for species measured by more than one of these instruments. The GC instruments were all in agreement to within 10-20% (slope) with coefficients of variation (r2) of > or = 0.85. The PTR-MS agreement with other instruments was more dependent on species with some very good agreements (r2 values of approximately 0.95 for some aromatics), but isoprene, acetaldehyde and propene were substantially less highly correlated (0.55 < r2 < 0.80). At least part of these differences were undoubtedly due to the timing of sample acquisition in an environment in which VOC levels changed very rapidly on both quantitative and temporal scales.
[Boscaini2004a] "Investigation of fundamental physical properties of a polydimethylsiloxane (PDMS) membrane using a proton transfer reaction mass spectrometer (PTRMS)",
International Journal of Mass Spectrometry
, vol. 239, no. 2: Elsevier, pp. 179–186, 2004.
A membrane introduction proton transfer reaction mass spectrometer (MI-PTRMS) has been employed for the characterisation of a polydimethylsiloxane (PDMS) membrane. For this purpose the diffusion and partition coefficients (which serve as a measure for solubility) have been determined experimentally for different classes of chemical compounds both non-polar and polar species, i.e., aromatics, alcohols, and ketones. It turned out that not only polar compounds exhibit strong interaction with a hydrophobic membrane such as the PDMS, but also non-polar compounds as trimethylbenzene or propylbenzene show strong interaction with a PDMS membrane. Stronger analyte–membrane interaction leads to a slower diffusion coefficient and larger partition coefficient. The effect of the temperature on the diffusion coefficient and partition coefficient has also been investigated, i.e., at higher temperature diffusion becomes faster and solubility lower. Permeability can be calculated from diffusion and partition coefficients and the activation energy has been derived from corresponding Arrhenius plots. The MI-PTRMS system shows detection limits in the order of tens of pptv and its response is linear for more than four orders of magnitude.
[Williams2004] "Measurements of organic species in air and seawater from the tropical Atlantic",
Geophysical research letters
, vol. 31, no. 23: Wiley Online Library, 2004.
A West -East crossing of the Tropical Atlantic during Meteor cruise 55 included measurements of organic species within the atmospheric marine boundary layer and the upper ocean. Acetone, methanol, acetonitrile and DMS were measured between 10–0°N and 35°W–5°E, on either side of the ITCZ. Methanol and acetone concentrations were higher in the northern hemisphere, both in surface seawater and the atmosphere whereas acetonitrile and DMS showed no significant interhemispheric gradient. Three depth profiles from 0–200 m for these species were measured. Acetone, methanol, DMS and acetonitrile generally decreased with depth with the sharpest decrease in concentration in all profiles being found at the bottom of the mixed layer. The average air mixing ratios and surface seawater concentrations for the whole dataset are respectively: acetone 0.53 nmol/mol and 17.6 nmol/L; acetonitrile 0.11 nmol/mol and 6.19 nmol/L; methanol 0.89 nmol/mol and 118.4 nmol/L; and DMS 0.05 nmol/mol and 1.66 nmol/L.
[Boscaini2004b] "Membrane inlet proton transfer reaction mass spectrometry (MI-PTRMS) for direct measurements of VOCs in water",
International Journal of Mass Spectrometry
, vol. 239, no. 2: Elsevier, pp. 171–177, 2004.
The use of a membrane inlet proton transfer reaction mass spectrometry (MI-PTRMS) system was investigated for the quantitative analysis of VOCs directly from water. Compounds playing an important role in environmental, biological and health issues such as methanol, acetonitrile, acetone, dimethylsulfide (DMS), isoprene, benzene, and toluene have been analyzed both in fresh and salty water. The system shows very good sensitivity, reproducibility, and a linear response of up to five orders of magnitude. The detection limit for DMS is about 100 ppt and for methanol is about 10 ppb both in fresh and salty water. The response time of the various compounds across the membrane is on the order of a few minutes. This fast response and the fact that the PTRMS can perform absolute measurements without the necessity of calibration make the system suitable for on-line and -site measurements of VOCs directly from water.
[Roberts2004] "Nosespace analysis with proton-transfer-reaction mass spectrometry: intra-and interpersonal variability",
Handbook of flavor characterization: sensory analysis, chemistry, and physiology
, vol. -, pp. 151–162, 2004.
[Hayward2004] "Online analysis of volatile organic compound emissions from Sitka spruce (Picea sitchensis).",
, vol. 24, no. 7: Institute of Environmental and Natural Sciences, Lancaster University, Lancaster, LA1 4YQ, U.K., pp. 721–728, Jul, 2004.
Volatile organic compound (VOC) emissions from Sitka spruce (Picea sitchensis Bong.) growing in a range of controlled light and temperature regimes were monitored online with a proton transfer reaction-mass spectrometer (PTR-MS) operating at a temporal resolution of approximately 1 min. Isoprene emissions accounted for an average of more than 70% of measured VOCs and up to 3.5% of assimilated carbon. Emission rates (E) for isoprene correlated closely with photosynthetic photon flux (PPF) and temperature, showing saturation at a PPF of between 300 and 400 micromol m(-2) s(-1) and a maximum between 35 and 38 degrees C. Under standard conditions of 30 degrees C and 1000 micromol m(-2) s(-1) PPF, the mean isoprene E was 13 microg gdm(-1) h(-1), considerably higher than previously observed in this species. Mean E for acetaldehyde, methanol and monoterpenes at 30 degrees C were 0.37, 0.78 and 2.97 microg gdm(-1) h(-1), respectively. In response to a sudden light to dark transition, isoprene E decreased exponentially by > 98% over about 3 h; however, during the first 7 min, this otherwise steady decay was temporarily but immediately depressed to approximately 40% of the pre-darkness rate, before rallying during the following 7 min to rejoin the general downward trajectory of the exponential decay. The sudden sharp fall in isoprene E was mirrored by a burst in acetaldehyde E. The acetaldehyde E maximum coincided with the isoprene E minimum (7 min post-illumination), and ceased when isoprene emissions resumed their exponential decay. The causes of, and linkages between, these phenomena were investigated.
[Schade2004] "OVOC emissions from agricultural soil in northern Germany during the 2003 European heat wave",
, vol. 38, no. 36: Elsevier, pp. 6105–6114, 2004.
Fluxes of methanol and acetone were measured from an agricultural field plot during one of the hottest weeks of the heat wave of the summer of 2003 in Europe. Significant positive fluxes from the bare, plowed soil for these oxygenated volatile organic compounds were found. Methanol fluxes ranged from 0 to 0.20 mg C m−2 h−1 while acetone fluxes ranged from −0.01 to 0.05. Mixing ratios for both methanol and acetone showed significant increases at night, consistent with a ground-based emission source for both the compounds. Methanol emissions were well correlated with sensible heat flux, peaking around noon. Assuming abiological production from soil organic matter in the topsoil, we calculate that 48 kJ mol−1 of energy is required to liberate the methanol from the topsoil. In contrast to methanol, acetone fluxes were not correlated with any measured meteorological parameter. This suggests that acetone has another source and may be produced in the soil subsurface, possibly through biological or moisture-driven processes. Using the flux data, we also simulated relaxed eddy accumulation (REA) experiments and reconfirm that sonic temperature can be used to calculate b-factors for REA analysis of a variety of trace gas fluxes.
[Steinbacher2004] "Performance characteristics of a proton-transfer-reaction mass spectrometer (PTR-MS) derived from laboratory and field measurements",
International Journal of Mass Spectrometry
, vol. 239, no. 2: Elsevier, pp. 117–128, 2004.
Volatile organic compounds (VOCs) play an important role in the formation of ozone and aerosols in the atmosphere. In an increasing number of field campaigns the proton-transfer-reaction mass spectrometer (PTR-MS) has proven to be a useful and fast tool for measuring VOCs and studying the relevant atmospheric processes. This work describes laboratory and field measurements with two different versions of the PTR-MS and presents important instrument specific features. The temperature stabilization and the change of the gasket material in the newer version significantly improved the performance of the instrument, as demonstrated by periodical background measurements under field conditions. The investigation of the mass discrimination illustrated the necessity of an elaborate verification. The humidity dependence of benzene was substantially lower than in former studies, which used higher drift tube pressures, but it is still higher than predicted by a simple dimer/monomer equilibrium model. An instrument comparison with a fluorescent technique was performed for formaldehyde and showed differences between pure formaldehyde calibration gases and complex ambient air samples. An intercomparison of two PTR-MSs measuring ambient air yielded satisfactory results after calibration for most of the considered masses. Comparing PTR-MS and gas chromatograph measurements of aromatic compounds, revealed a good agreement for conditions of fresh anthropogenic emissions. In photochemically aged air, many masses detected by the PTR-MS are not only influenced by anthropogenically and biogenically emitted but also oxidized VOCs.
[Hansel2004] "Proton transfer mass spectrometer",
, vol. 35, no. 6, pp. 197–199, 2004.
[Critchley2004] "The proton transfer reaction mass spectrometer and its use in medical science: applications to drug assays and the monitoring of bacteria",
International Journal of Mass Spectrometry
, vol. 239, no. 2: Elsevier, pp. 235–241, 2004.
Proton transfer reaction mass spectrometry (PTR-MS) enables monitoring of trace gases in air with high sensitivity without major gases interfering. In this paper, we present the potential use of a proton transfer reaction mass spectrometer for two medical applications; the monitoring of drugs and bacterial infection. The first study illustrates a feasibility trial to monitor the intravenous anaesthetic agent 2,6-di-isopropyl phenol (propofol), and two of its metabolites, on the breath of patients in real-time during surgery. Propofol is a commonly used intravenous anaesthetic. However, there is no method of instantaneously monitoring the plasma concentration of the agent during surgery, and therefore determining whether or not the plasma level is of such a value to ensure that the patient is correctly anaesthetized. That propofol and its metabolites were monitored in real-time using the PTR-MS suggests possibilities for routine intravenous anaesthesia monitoring analogous to that for volatile anaesthetic agents. In addition to the above work we also investigated proton transfer to another anaesthetic, sevoflurane. Comparisons between PTR-MS and selected ion flow tube (SIFT) investigations are presented. The second study presented in this paper investigated the volatile organic compounds emitted by microbial cell cultures. The objective was to show that different microbial cultures could be readily distinguished from the resulting mass spectra recorded using the PTR-MS. The initial results are encouraging, which taken together with the real-time analysis and high sensitivity of the PTR-MS, means that proton transfer reaction mass spectrometry has the potential to characterise bacterial infection rapidly.
[Ezra2004] "Proton transfer reaction-mass spectrometry as a technique to measure volatile emissions of Muscodor albus",
, vol. 166, no. 6: Elsevier, pp. 1471–1477, 2004.
Muscodor albus is an endophytic fungus that produces volatile organic compounds (VOCs) that both inhibit and kill other microorganisms. This fungus is now being used to treat human wastes and disinfest soils of plant disease causing organisms. The development of a method to accurately determine the quantity and quality of volatiles being emitted by this organism is critical for optimizing its application as an antimicrobial agent. Proton transfer reaction-mass spectrometry (PTR-MS) was used to monitor the concentration of VOCs emitted by M. albus. This on-line technique is fast, accurate and provides data at the detection limits of ppb. Production of VOCs is temperature dependent with decreased gas production occurring at higher temperatures. The technique was also applied to soils containing M. albus along with the plant pathogen Pythium ultimum and it was possible to successfully monitor VOC production in situ.
[Steeghs2004] "Proton-transfer-reaction mass spectrometry as a new tool for real time analysis of root-secreted volatile organic compounds in Arabidopsis.",
, vol. 135, no. 1: Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80305, USA., pp. 47–58, May, 2004.
Plant roots release about 5% to 20% of all photosynthetically-fixed carbon, and as a result create a carbon-rich environment for numerous rhizosphere organisms, including plant pathogens and symbiotic microbes. Although some characterization of root exudates has been achieved, especially of secondary metabolites and proteins, much less is known about volatile organic compounds (VOCs) released by roots. In this communication, we describe a novel approach to exploring these rhizosphere VOCs and their induction by biotic stresses. The VOC formation of Arabidopsis roots was analyzed using proton-transfer-reaction mass spectrometry (PTR-MS), a new technology that allows rapid and real time analysis of most biogenic VOCs without preconcentration or chromatography. Our studies revealed that the major VOCs released and identified by both PTR-MS and gas chromatography-mass spectrometry were either simple metabolites, ethanol, acetaldehyde, acetic acid, ethyl acetate, 2-butanone, 2,3,-butanedione, and acetone, or the monoterpene, 1,8-cineole. Some VOCs were found to be produced constitutively regardless of the treatment; other VOCs were induced specifically as a result of different compatible and noncompatible interactions between microbes and insects and Arabidopsis roots. Compatible interactions of Pseudomonas syringae DC3000 and Diuraphis noxia with Arabidopsis roots resulted in the rapid release of 1,8-cineole, a monoterpene that has not been previously reported in Arabidopsis. Mechanical injuries to Arabidopsis roots did not produce 1,8-cineole nor any C6 wound-VOCs; compatible interactions between Arabidopsis roots and Diuraphis noxia did not produce any wound compounds. This suggests that Arabidopsis roots respond to wounding differently from above-ground plant organs. Trials with incompatible interactions did not reveal a set of compounds that was significantly different compared to the noninfected roots. The PTR-MS method may open the way for functional root VOC analysis that will complement genomic investigations in Arabidopsis.
[Hartungen2004] "Proton-transfer-reaction mass spectrometry (PTR-MS) of carboxylic acids: Determination of Henry's law constants and axillary odour investigations",
International Journal of Mass Spectrometry
, vol. 239, no. 2: Elsevier, pp. 243–248, 2004.
Proton-transfer-reaction mass spectrometry (PTR-MS) was used as an analytical tool to measure gas-phase concentrations of short-chain fatty acids. Chemical ionisation of C2single bondC6 carboxylic acids by PTR-MS produced intense protonated molecular ions (with traces of hydrates) along with acylium ion fragments. Gas-phase concentrations were derived using the established method for calculating PTR-MS sensitivity factors. Henry's law constants of carboxylic acids for aqueous solutions at 40 °C were determined. Direct monitoring of volatile fatty acids, known to be associated with secretions from the human axilla, was performed via a specially designed transfer device situated in the axilla. Mass spectral data corresponded with the findings of a sensory assessor.
[Biasioli2004] "PTR-MS monitoring of odour emissions from composting plants",
International journal of mass spectrometry
, vol. 239, no. 2: Elsevier, pp. 103–109, 2004.
We studied the possibility of monitoring with proton transfer reaction-mass spectrometry (PTR-MS) odours emitted in various situations related to composting plants of municipal solid waste (MSW), i.e., waste storage, waste management, and biofilters. Comparison of PTR-MS volatile profiles of the gaseous mixtures entering and exiting a biofilter suggests the possibility of fast and reliable monitoring biofilter efficiency. Moreover, we investigated the relationships between the olfactometric assessment of odour concentration and PTR-MS spectral line intensity finding a positive correlation between the former and several masses and their overall intensity. The application of multivariate calibration methods allows to determine odour concentrations based only on PTR-MS instrumental data. The possibility of avoiding the use of time consuming and expensive olfactometric methods and applications in monitoring waste treatments plants and, in particular, of biofilters is suggested.
[Jaksch2004a] "Quality control of a herb extract using PTR-MS",
International Journal of Mass Spectrometry
, vol. 239, no. 2: Elsevier, pp. 203–207, 2004.
We have developed an objective method for the determination of a herb extract's quality based on headspace measurements by proton-transfer-reaction mass spectrometry (PTR-MS); this quality was checked by a sensory analysis until now. This novel method enables the company ‘Bionorica’ to ensure that they are only selling high-quality products and therefore avoid complaints of the customer. The method could be also used for controlling and optimising the production process.
[Zhao2004] "Quantification of hydroxycarbonyls from OH-isoprene reactions.",
J Am Chem Soc
, vol. 126, no. 9: M University, College Station, Texas 77843, USA. email@example.com, pp. 2686–2687, Mar, 2004.
Hydroxycarbonyls arising from OH-initiated reactions of isoprene have been quantified by the technique of a flow reactor coupled to proton-transfer reaction mass spectrometry (PTR-MS) detection. The yields of C5- and C4-hydroxycarbonyls are (19.3 +/- 6.1)% and (3.3 +/- 1.6)%, respectively, measured at a flow tube pressure of about 100 Torr and at a temperature of 298 +/- 2 K. A yield of (8.4 +/- 2.4)% is obtained for the unsaturated carbonyl C5H8O, confirming that internal OH addition represents the minor channel in the initial OH-isoprene reaction. The results show that those carbonyl compounds account for the most previously unquantified carbon, enabling the isoprene carbon closure. The study also reveals novel aspects of the delta-hydroxyalkoxy radical degradation mechanism, which is essential for modeling tropospheric O3 formation. In addition, this work demonstrates the application of PTR-MS for quantification of products of hydrocarbon reactions, which should have profound impacts on elucidation of the chemistry of atmospheric anthropogenic and biogenic hydrocarbons.
[Lirk2004] "Quantification of recent smoking behaviour using proton transfer reaction-mass spectrometry (PTR-MS).",
Wien Klin Wochenschr
, vol. 116, no. 1-2: Department of Anesthesiology and Critical Care Medicine, Clinical Division of General Internal Medicine, Leopold-Franzens University, Innsbruck, Austria., pp. 21–25, Jan, 2004.
Smoking is the most important single risk factor in current public health. Surveillance of exposure to tobacco smoke may be accomplished using environmental monitoring or in-vivo tests for smoking biomarkers. Acetonitrile exhaled in human breath has been described as a potential marker mirroring recent smoking behavior. The aim of this study was to determine exhaled acetonitrile levels in a sample of 268 volunteers (48 smokers, 220 non-smokers) attending a local health fair. Breath specimens were collected into inert sample bags, with parallel collection of ambient air. Subsequently, all samples were analysed using proton transfer reaction-mass spectrometry (PTR-MS). Smokers had elevated levels of exhaled acetonitrile compared with non-smokers (p<0.001). Analysis using the receiver-operating-characteristic curve demonstrated that smoking can be predicted with a sensitivity of 79% and a specificity of 91%, using a cut-off concentration of 20.31 parts per billion of acetonitrile. This first field survey of exhaled acetonitrile in a large group of test persons demonstrates the feasibility of a rapid and non-invasive test for recent exposure to tobacco. We conclude that analysis of exhaled-breath acetonitrile may serve as a method of determining recent active smoking behaviour.
[Schoberberger2004] "Quantification of recent smoking behaviour using Proton Transfer Reaction-Mass Spectrometry (PTR-MS).",
Wien Klin Wochenschr
, vol. 116, no. 5-6, pp. 209; author reply 209–209; author reply 210, Mar, 2004.
Heutzutage gilt Rauchen als der wichtigste medizinische Risikofaktor. Die Überwachung einer Exposition gegenüber Tabakrauch kann im Prinzip mittels Umluftmessungen, oder direkt mit Hilfe von Biomarkern erfolgen. Acetonitrile wurde als ein potentieller Marker für das rezente Raucherverhalten beschrieben. Es war daher das Ziel vorliegender Studie, die in der Ausatemluft festgestellten Acetonitrile-Konzentrationen in einem Kollektiv von 268 Personen (48 Raucher, 220 Nichtraucher) festzustellen. Atemgasproben wurden in inerten Sammelgefäßen gesammelt, und die Konzentration von Acetonitrile in der Umluft während der Abnahmen wurde parallel erhoben. Die Analyse der Umluft- und Atemluftproben erfolgte mittels Protonen Transfer Reaktions-Massenspektrometrie (PTR-MS). Raucher zeigten in der Ausatemluft signifikant erhöhte Acetonitrilekonzentrationen im Vergleich zu Nichtrauchern (p<0,001). Die Erstellung einer receiver-operating-characteristic curve ergab für die Unterscheidung von Rauchern und Nichtrauchern mittels PTR-MS eine Sensitivität von 79% und eine Spezifität von 91% bei einem Schwellenwert von 20.31 parts per billion. Diese erste Feldstudie zum Thema Acetonitrile in einem großen Testkollektiv konnte die Praktikabilität dieses Markers als schnellen und nichtinvasiven Test rezenten Raucherverhaltens nachweisen. Wir schlussfolgern, dass die Analyse der Atemgaskonzentration von Acetonitrile Rückschlüsse auf das aktive Raucherverhalten ziehen lässt.
[Beauchamp2004] "Short-term measurements of CO, NO, NO< sub> 2, organic compounds and PM< sub> 10 at a motorway location in an Austrian valley",
, vol. 38, no. 16: Elsevier, pp. 2511–2522, 2004.
In situ measurements of CO, NOx, PM10 and certain organic compounds took place over an 11 day period encompassing a 12 h motorway blockade. Located within the Inn valley (Tirol, Austria), the monitoring site experiences varying meteorological conditions and traffic frequency throughout the day which both strongly influence air pollutant levels. Early morning increases of NOx, PM10 and aromatic hydrocarbons were clearly correlated with rising traffic. Midday minima and afternoon maxima may be explained by changing wind conditions and varying inversion layer dynamics. Night time lows in concentrations can be explained by minimal traffic activity. Classification of compound sources was made through grouping of data, separated into times when heavy duty vehicles (HDV) were permitted to use the motorway and HDV-ban periods. Increased levels of NOx and PM10 were observed from data that included periods of high HDV numbers, with levels decreasing significantly during HDV-ban periods. In contrast, the aromatic hydrocarbons and CO displayed only minor variations between these two periods. Furthermore, on typical workdays NOx levels reached a maximum that corresponded to a peak in HDV numbers, whereas the aromatic compounds peaked later when LDV numbers had reached their maximum. Our findings give strong evidence that increased NOx and PM10 levels can be predominantly attributed to HDV traffic. Principal components analyses for the separated data further support this conclusion.
[Graus2004] "Transient release of oxygenated volatile organic compounds during light-dark transitions in grey poplar leaves",
, vol. 135, no. 4: American Society of Plant Biologists, pp. 1967–1975, 2004.
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.
[Warneke2004] "Two additional advantages of proton-transfer ion trap mass spectrometry.",
Rapid Commun Mass Spectrom
, vol. 18, no. 1, pp. 133–134, 2004.
[Kato2004] "Urban air measurements using PTR-MS in Tokyo area and comparison with GC-FID measurements",
International Journal of Mass Spectrometry
, vol. 235, no. 2: Elsevier, pp. 103–110, 2004.
Ambient air at a suburban area in Tokyo was measured by proton transfer reaction mass spectrometry (PTR-MS) and GC-FID simultaneously. Good correlations were obtained for hydrocarbon concentrations between GC-FID and PTR-MS, but concentrations differed by factor of 0.52–2.15, depending on the hydrocarbon. This shows that the calculated PTR-MS data needs to be corrected by standard gas measurements. Isoprene measured by PTR-MS is influenced by other species and the results of isoprene is not reliable at low concentration. Oxygenated volatile organic carbons showed higher concentrations during summer than in fall. This reflects the enhanced photochemical reactivity in summer. On the other hand, aromatic hydrocarbons, emitted mainly from car exhaust, did not show a difference between summer and fall. The ratios of aromatic hydrocarbons can be used as an indicator of photochemical reaction. Enhanced photochemical reactions were expected from these ratios during summer.
[Steinbrecher2004] "Vegetation-atmospheric interactions: The emissions of biogenic volatile organic compounds (BVOC) and their relevance to atmospheric particle dynamics",
Biogeochemistry of Forested Catchments in a Changing Environment: A Case Study in NE-Bavaria, Germany, Ecol. Stud, vol. 172, pp. 215–232, 2004.