Infrared Laser Absorption Spectroscopy Research Articles

Kinetics and Mechanism of the Singlet Oxygen Atom Reaction with Dimethyl Ether.

We combine in situ laser spectroscopy, quantum chemistry, and kinetic calculations to study the reaction of a singlet oxygen atom with dimethyl ether. Infrared laser absorption spectroscopy and Faraday rotation spectroscopy are used for the detection and quantification of the reaction products OH, H2O, HO2, and CH2O on submillisecond time scales. Fitting temporal profiles of products with simulations using an in-house reaction mechanism allows product branching to be quantified at 30, 60, and 150 Torr. The experimentally determined product branching agrees well with master equation calculations based on electronic structure data and transition state theory. The calculations demonstrate that the dimethyl peroxide (CH3OOCH3) generated via O-insertion into the C-O bond undergoes subsequent dissociation to CH3O + CH3O through energetically favored reactions without an intrinsic barrier. This O-insertion mechanism can be important for understanding the fate of biofuels leaking into the atmosphere and for plasma-based biofuel processing technologies.

Mapping gas–phase CO<sub>2</sub> in the headspace of two champagne glasses through infrared laser absorption spectroscopy: ŒnoXpert glass versus INAO glass

Mapping gas–phase CO<sub>2</sub> in the headspace of two champagne glasses through infrared laser absorption spectroscopy: ŒnoXpert glass versus INAO glass

Optical pressure sensing at MHz rates via collisional line broadening of carbon monoxide: uncertainty quantification in reacting flows

An optical method for high-speed line-of-sight pressure measurements using infrared laser absorption spectroscopy is presented with detailed uncertainty analysis related to thermodynamic and compositional variation in combustion environments. The technique exploits simultaneous sub-microsecond sensing of temperature and mole fraction to extract pressure from collisional line broadening at MHz rates. A distributed-feedback quantum-cascade laser near 5 upmu m in a bias-tee circuit is used to spectrally resolve multiple rovibrational transitions in the P-branch of the fundamental band of carbon monoxide, which may be seeded or nascent to reacting flows. A comprehensive approach for estimating collisional line broadening in complex combustion gas mixtures is presented. Uncertainty is quantified for a wide range of conditions, reflecting different fuels, equivalence ratios, reaction progress, and combustion modes (deflagration and detonation), which influence gas composition and temperature. The sensor was evaluated for accuracy and precision in both a high-enthalpy shock-tube facility in hydrocarbon–air ignition experiments and behind ethylene–oxygen detonation waves in a detonation-impulse tube facility at temperatures from 1500 to 3000 K and pressures from 0.5 to 10 bar. Pressure measurements were compared to measurements by piezoelectric pressure transducers and to theoretical estimates from normal-shock and Chapman-Jouguet simulations. The high-speed path-integrated optical pressure measurement offers an alternative to traditional electromechanical transducers that are constrained to values at wall boundaries and have proven unreliable in some harsh reacting flows.

Multi-line Boltzmann regression for near-electronvolt temperature and CO sensing via MHz-rate infrared laser absorption spectroscopy

Multi-line Boltzmann regression for near-electronvolt temperature and CO sensing via MHz-rate infrared laser absorption spectroscopy

High-Precision Triple Oxygen Isotope Analysis of Carbon Dioxide by Tunable Infrared Laser Absorption Spectroscopy.

Precision measurements of the stable isotope ratios of oxygen (18O/16O and 17O/16O) in CO2 are critical to atmospheric monitoring and terrestrial climate research. High-precision 17O measurements by isotope ratio mass spectrometry (IRMS) are challenging because they require complicated sample preparation procedures, long measurement times, and relatively large samples sizes. Recently, tunable infrared laser direct absorption spectroscopy (TILDAS) has shown significant potential as an alternative technique for triple oxygen isotope analysis of CO2, although the ultimate level of reproducibility is unknown, partly because it is unclear how to relate TILDAS measurements to an internationally accepted isotope abundance scale (e.g., VSMOW2-SLAP2). Here, we present a method for high-precision triple oxygen isotope analysis of CO2 by TILDAS, requiring ∼8-9 μmol of CO2 (or 0.9 mg carbonate) in 50 min, plus ∼1.5 h for sample preparation and dilution of CO2 in N2 to a nominal 400 μmol mol-1. Overall reproducibility of Δ'17O (CO2) was 0.004‰ (4 per meg) for IAEA603 (SE, n = 6) and 10 per meg for NBS18 (SE, n = 4). Values corrected to the VSMOW2-SLAP2 scale are in good agreement with established techniques of high-precision IRMS, with the exception of Δ'17O measured by platinum-catalyzed exchange of CO2 with O2. Compared to high-precision IRMS, TILDAS offers the advantage of times less sample, and greater throughput, without loss of reproducibility. The flexibility of the technique should allow for many important applications to global biogeochemical monitoring and investigation of 17O anomalies in a range of geological materials.

Real-time methods of hydrogen sulfide detection

A comparative analytical review of existing methods and means of measuring hydrogen sulfide content in gasses was performed. The method of infrared laser absorption spectroscopy, which uses semiconductor diode lasers tunable in the mid-infrared range as emission sources, is proving to be one of the most promising methods for solving these problems.

Subnanomolar Sensitive Stable Isotopic Determination in CO2 by Tunable Infrared Laser Absorption Spectroscopy.

Oxygen and carbon stable isotope ratios (18O/16O, 13C/12C, and 17O/16O) of CO2 have been crucial in helping us understand Earth and planetary systems. These ratios have also been used in medicine for the noninvasive diagnosis of diseases from exhaled breath and for quantifying biochemical or metabolic reactions and in determining the production area of agricultural products. The current method for measuring the stable isotope ratios of CO2 is primarily gas-source isotope ratio mass spectroscopy (IRMS). Due to the recent demand for isotopic microanalysis of carbonates and organic compounds, the sample size required for isotopic measurements has been reduced to approximately 2 nmol CO2 (equivalent to 0.2 μg CaCO3 and 24 ng carbon) by using high-precision IRMS. We report a novel method using tunable mid-infrared laser direct absorption spectroscopy (TILDAS) for sensitive measurements of 18O/16O and 13C/12C in subnanomolar CO2. This method can accurately measure 18O/16O and 13C/12C in CO2 with a repeatability of less than 0.03‰ (n = 28) in a range of 0.3 nmol (equivalent to 0.03 μg CaCO3 and 3.8 ng carbon) to 30 nmol. This is a sample size 1 order of magnitude smaller than currently available sensitive analytical techniques. In addition, the TILDAS system measures 17O/16O simultaneously with a repeatability of less than 0.06‰ (n = 28). Our method is a major advance in supersensitive CO2 stable isotopic analyses for various fields.

Synchronic measurements of temperatures and concentrations of OH, NH, and NO in flames based on broadband ultraviolet absorption spectroscopy

Temperature is an important parameter influencing the combustion reaction path and rate and determining the combustion and energy exchange efficiency. The OH, NH, NO and other species are involved in the key elementary reactions of combustion and determine the generation of NO<i><sub>x</sub></i> pollutants. Therefore, temperature and concentration measurements of OH, NH, and NO are of great significance for combustion diagnostics and research on reaction or emission mechanisms. In this work, a measurement system with high spatial resolution based on broadband ultraviolet absorption spectroscopy is established to realize simultaneous measurements of the temperature and concentrations of OH, NH, and NO in flames. Low detection limits of these three species are achieved by using the established measurement method. The 1<i>σ</i> detection limit of NH is 1.8 ppb·m (1560 K), which is realized for the first time in atmospheric-pressure flames using absorption spectroscopy. The 1<i>σ</i> detection limits of OH and NO are 60 ppb·m (1590 K) and 1 ppm·m (1380 K), respectively, which are obviously better than the existing results obtained by using infrared laser absorption spectroscopy. Then, the distributions of temperatures and concentrations of OH, NO and NH are acquired at various heights in an atmospheric-pressure NH<sub>3</sub>/CH<sub>4</sub>/air premixed flat flame with a high spatial resolution of nearly 0.1 mm. The broadband absorption spectra of OH and NH are acquired simultaneously inside the flame front, and the spectra of OH and NO are acquired simultaneously above the flame front. Inside or near the flame front, the temperatures deduced from the spectra of OH, NH, and NO are consistent, verifying the ability of these three species to be used to measure temperature. In addition, OH, NH, and NO are found to be suitable for different regions in combustion. The OH absorption is suitable for the post-combustion region with temperatures higher than 1000 K, the NH absorption can be used to acquire the temperature inside the flame front in complex combustion, and the NO absorption was able to provide the temperature in the region before or outside combustion at lower temperatures. Additionally, the experimental temperature and concentration profiles are in good agreement with the computational fluid dynamics predictions based on the mechanism, exhibiting the accuracy of the simultaneous temperature and concentration measurements by using broadband ultraviolet absorption spectra. Moreover, the differences in temperature and OH concentration between experiments and simulations indicate that the carbon sub-mechanism in the mechanism given by Okafor et al. [Okafor E C, Naito Y, Colson S, Ichikawa A, Kudo T, Hayakawa A, Kobayashi H <ext-link ext-link-type="uri" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://doi.org/10.1016/j.combustflame.2017.09.002">2018 <i>Combust. Flame</i> <b>187</b> 185</ext-link>] should be further improved for more accurate predictions of NH<sub>3</sub>/CH<sub>4</sub> combustion.

Data Pre-Processing of Infrared Spectral Breathprints for Lung Cancer Detection.

Though breath analysis shows promise as a noninvasive and cost-effective approach to lung cancer screening, biomarkers in exhaled breath samples can be overwhelmed by irrelevant internal and environmental volatile organic compounds (VOCs). These extraneous VOCs can obscure the disease signature in a spectral breathprint, hindering the performance of pattern recognition models. In this work, pre-processing pipelines consisting of missing value replacement, detrending, and normalization techniques were evaluated to reduce these effects and enhance the features of interest in infrared cavity ring-down spectra. The best performing pipeline consisted of moving average detrending, linear interpolation for missing values, and vector normalization. This model achieved an average accuracy of 73.04% across five types of classifiers, exhibiting an 8.36% improvement compared to a baseline model (p < 0.05). A linear support vector machine classifier yielded the best performance (79.75% accuracy, 67.74% sensitivity, 87.50% specificity). This work can serve to guide pre-processing in future lung cancer breath research and, more broadly, in infrared laser absorption spectroscopy in general.

APPLICABILITY OF THE SPECTROSCOPY IN THE ANALYSIS OF SCUBA DIVERS RESPIRATION

Scuba diving could increase free radicals production which acts as signaling molecules to induce adaptation against oxidative attack. The aim of the new research was to study the impact of scuba diving effects on multiple gas composition responses from the exhaled breath of professional divers. Ethylene, ammonia, and carbon dioxide concentrations from diver s respiration were measured before and after the immersion to 8 m depth in the Black Sea. The ethylene gas (for oxidative stress condition), the ammonia gas (for proteins degradation) and the carbon dioxide gas from the respiration of the six divers were evaluated by mean of the breath test using infrared laser absorption spectroscopy. The experimental results for each breath test of scuba divers will be presented and discussed.

Influence of the Active Screen Plasma Power during Afterglow Nitrocarburizing on the Surface Modification of AISI 316L

Active screen plasma nitrocarburizing (ASPNC) increases the surface hardness and lifetime of austenitic stainless steel without deteriorating its corrosion resistance. Using an active screen made of carbon opens up new technological possibilities that have not been exploited to date. In this study, the effect of screen power variation without bias application on resulting concentrations of process gas species and surface modification of AISI 316L steel was studied. The concentrations of gas species (e.g., HCN, NH3, CH4, C2H2) were measured as functions of the active screen power and the feed gas composition at constant temperature using in situ infrared laser absorption spectroscopy. At constant precursor gas composition, the decrease in active screen power led to a decrease in both the concentrations of the detected molecules and the diffusion depths of nitrogen and carbon. Depending on the gas mixture, a threshold of the active screen power was found above which no changes in the expanded austenite layer thickness were measured. The use of a heating independent of the screen power offers an additional parameter for optimizing the ASPNC process in addition to changes in the feed gas composition and the bias power. In this way, an advanced process control can be established.

Effect of the admixture of N2 to low pressure, low temperature H2-CH4-CO2 microwave plasmas used for large area deposition of nanocrystalline diamond films

In a distributed antenna array reactor, microwave H2-CH4-CO2 plasmas with admixture of N2 used for the low-temperature deposition of nanocrystalline diamond (NCD) films are studied by in situ infrared laser absorption spectroscopy (LAS) and optical emission spectroscopy techniques. The experiments are carried out in order to analyze the dependence of temperatures and species densities as a function of the admixture of nitrogen. The evolution of the concentrations of the methyl radical (CH3), and of five stable molecules (NH3, HCN, CH4, C2H2, and CO), are monitored in the plasma processes by LAS using tunable lead salt diode lasers and external-cavity quantum cascade lasers (EC-QCL) as radiation sources. OES is performed simultaneously to obtain complementary information about (i) the degree of dissociation of H2 precursor gas, (ii) the gas temperature and therefore (iii) the density of atomic hydrogen, a key species in the chemistry of NCD deposition plasmas. The species temperatures are not significantly affected by the nitrogen addition. The concentrations of the various species are in the range between 1011 to 1015 molecules cm−3. HCN and CO are the major products in the plasma besides atomic hydrogen. The analysis of the nitrogen and carbon mass balances of the measured species shows that in addition to NH3 and HCN other nitrogen containing species are produced in the plasma which were not probed. It is shown that the formation of HCN consumes C atoms that can be provided from hydrocarbon species and from the deposition of carbon-containing films on the reactor walls, which results in a decrease of the measured densities of hydrocarbon species.

Spectroscopic study of plasma nitrocarburizing processes with an industrial-scale carbon active screen

The active screen plasma nitrocarburizing technology is an improvement of conventional plasma nitrocarburizing by providing a homogeneous temperature distribution within the workload and reducing soot formation. In this study, an industrial-scale active screen (AS) made of carbon-fibre-reinforced carbon serves as the cathode as well as the carbon source for the plasma-chemical processes taking place. The pulsed dc discharge was maintained at a few mbar of pressure while simultaneously being fed with a mixed gas flow of hydrogen and nitrogen ranging from 10 to 100 slh. Using in situ infrared laser absorption spectroscopy with lead salt tuneable diode lasers and external-cavity quantum cascade lasers, the temperatures and concentrations of HCN, NH3, CH4, C2H2, and CO have been monitored as a function of pressure and total gas flow. To simulate industrial treatment conditions the temperature of the sample workload in the centre of the reactor volume was kept at 773 K by varying the plasma power at the AS between 6 and 8.5 kW. The resulting spectroscopically measured temperatures in the plasma agreed well with this value. Concentrations of the various species ranged from 6 × 1013 to 1 × 1016 cm−3 with HCN being the most abundant species.

Measurement of evaporation of hydrocarbon droplets by laser absorption spectroscopy

Concentration measurements of evaporated hydrocarbon species by infrared laser absorption spectroscopy at a monodisperse droplet chain are presented. A droplet generator was installed within a flow channel and operated with cyclohexane, iso-octane, n-heptane, n-pentane and 1-butanol. The flow channel was flushed with a laminar flow of air at different temperatures. The absorption of a HeNe laser beam at $$\lambda = 3.39\,\upmu \hbox {m}$$ traversing through the flow channel at varying distances from the droplet chain was exploited to determine the vapor concentrations of the hydrocarbons. Measurements of the absorption cross sections in a heated gas cell ($$T = 300$$–773 K) enabled the quantification of the absorption signals from the droplet chain. Vapor concentrations were determined in planes perpendicular to the droplet chain. From the increase of vapor concentration between the planes, the evaporation rate could be determined. The evaporation rates were measured in dependence of co-flow temperature, droplet velocity, droplet generation frequency and droplet spacing. In the investigated temperature range of the air (313–430 K) the evaporation rates increased linearly with temperature. The order of the fuels with respect to evaporation rates corresponded with the boiling points of the individual fuels. In addition to the presentation of the results, the paper discusses the performance of vapor concentration measurements by laser absorption spectroscopy at droplet chains which has not been tested before in such a configuration. Particular attention was paid to the spatial resolution of the measurement. The results are well suited to validate models and numerical simulations.

Characterization of high-explosive detonations using broadband infrared external cavity quantum cascade laser absorption spectroscopy

Infrared laser absorption spectroscopy provides a powerful tool for probing physical and chemical properties of high-explosive detonations. A broadly tunable swept-wavelength external cavity quantum cascade laser operating in the mid-wave infrared (MWIR) spectral region is used to measure transmission through explosive fireballs generated from 14 g charges of 4 different explosive types detonated in an enclosed chamber. Analysis of time-resolved transmission and emission at a 2 μs sampling rate shows the evolution of fireball infrared opacity in the first 10 ms after detonation. Broadband high-resolution absorption spectra acquired over the spectral range of 2050–2300 cm−1 (4.35–4.88 μm) at a 100 Hz rate are used to measure properties of fireball evolution over longer time scales out to 100 s. Path-integrated concentrations of combustion products CO, CO2, H2O, and N2O are measured and show evolutions over multiple time scales and significant differences between explosive types. Spectral analysis is used to characterize gas temperature and to measure broadband attenuation from absorption and scattering of particulates. Analysis of the results provides information on the MWIR optical properties, gaseous detonation/combustion products, and particulates throughout the explosive process including initial detonation, fireball expansion and cooling, and diffusive mixing in the chamber.

Solid carbon active screen plasma nitrocarburizing of AISI 316L stainless steel: Influence of N2-H2 gas composition on structure and properties of expanded austenite

Plasma nitrocarburizing based on active screen technology using a carbon-fiber reinforced carbon active screen was applied in an industrial-scale unit for thermochemical surface treatment of austenitic stainless steel. This concept is based on the use of a solid-carbon-source for the generation of highly reactive process gases directly in the active screen plasma. In this work, plasma nitrocarburizing of AISI 316L stainless steel was performed by means of the variation of the precursor gases H2 and N2 in the range of 0% N2 up to 100% N2 without the use of any additional carbon bearing gas. For a set of H2-N2 gas mixtures, the resulting reaction gas was monitored using infrared laser absorption spectroscopy (IRLAS). The four main stable species HCN, CH4, NH3 and C2H2 were detected. A detailed analysis of the surface microstructure resulting for each specific H2-N2 precursor gas mixture was performed. This included glow discharge optical emission spectroscopy (GDOES), optical microscopy, micro hardness measurements, as well as X-ray diffraction analysis.The concentrations of hydrocarbons CH4 and C2H2 were most abundant in case of pure hydrogen plasma, and a carbon-expanded austenite layer with hardness values up to 600 HK0.01 and smooth hardness gradient resulted. The admixture of N2 to the precursor gas significantly increased the concentrations of HCN and NH3. Due to this, a duplex structure of nitrogen-expanded austenite γN and carbon-expanded austenite γC formed. With increasing content of N2 up to 50% in the precursor gas, the resulting layer thickness increased and the hardness reached values up to 1300 HK0.01. At strong nitrogen excess in the precursor gas, the nitrogen concentration in the expanded austenite significantly increased, the Fe2–3(N, C) phase was formed, and simultaneously the layer thickness decreased. Structure and properties of the expanded austenite layer significantly changed by only varying the H2-N2 ratio of the precursor gas mixture.

Spectroscopic investigations of plasma nitrocarburizing processes using an active screen made of carbon in a model reactor

The active screen plasma nitrocarburizing technology significantly reduces the risk of cementite precipitation in the compound layer of nitrocarburized materials and of soot production compared to conventional plasma nitrocarburizing. In a laboratory-scaled plasma nitriding monitoring reactor, PLANIMOR, using an active screen made of carbon, low-pressure pulsed dc N2–H2 plasmas have been studied by infrared laser absorption spectroscopy (IRLAS) techniques. Applying IRLAS, using tunable diode lasers (TDL) and a quantum cascade laser (QCL) as radiation sources, the evolution of the concentrations of eight stable molecular reaction products, C2H2, C2H4, CH4, HCN, NH3, CO, C2H6, and C2N2, and of the CH3 radical, have been monitored. By using the line ratio method, the rotational temperatures of HCN and CO could be determined in a range of 300–400 K and 300–500 K, respectively. Analysing the profile of the CH3 Q(3-3) absorption line, the gas temperature of this radical, i.e. the temperature in the vicinity of the plasma zone, has been found to range between 400–800 K. The concentrations of the detected molecular reaction products were found to be in the range of 1012–1016 molecules cm−3 with HCN and NH3 as the most abundant reaction products. Additionally, the respective conversion efficiencies to the product molecules (RC ≈ 5 × 1012–2 × 1016 molecules J−1) have been determined for different mixing ratios of N2:H2 in the feed gas and plasma power values. Taking into account the concentrations of all carbon-containing species, a maximum of the carbon combustion of the screen material of up to 96 mg h−1 has been found for a N2–H2 ratio of 1:1 and the highest plasma power of the screen of Pscreen = 106 W.

On improved understanding of plasma-chemical processes in complex low-temperature plasmas

Over the last years, chemical sensing using optical emission spectroscopy (OES) in the visible spectral range has been combined with methods of mid infrared laser absorption spectroscopy (MIR-LAS) in the molecular fingerprint region from 3 to 20 μm, which contains strong rotational–vibrational absorption bands of a large variety of gaseous species. This optical approach established powerful in situ diagnostic tools to study plasma-chemical processes of complex low-temperature plasmas. The methods of MIR-LAS enable to detect stable and transient molecular species in ground and excited states and to measure the concentrations and temperatures of reactive species in plasmas. Since kinetic processes are inherent to discharges ignited in molecular gases, high time resolution on sub-second timescales is frequently desired for fundamental studies as well as for process monitoring in applied research and industry. In addition to high sensitivity and good temporal resolution, the capacity for broad spectral coverage enabling multicomponent detection is further expanding the use of OES and MIR-LAS techniques. Based on selected examples, this paper reports on recent achievements in the understanding of complex low-temperature plasmas. Recently, a link with chemical modeling of the plasma has been provided, which is the ultimate objective for a better understanding of the chemical and reaction kinetic processes occurring in the plasma.

High-Precision Simultaneous 18O/16O, 13C/12C, and 17O/16O Analyses for Microgram Quantities of CaCO3 by Tunable Infrared Laser Absorption Spectroscopy.

Stable isotope ratios (18O/16O, 13C/12C, and 17O/16O) in carbonates have contributed greatly to the understanding of Earth and planetary systems, climates, and history. The current method for measuring isotopologues of CO2 derived from CaCO3 is primarily gas-source isotope ratio mass spectroscopy (IRMS). However, IRMS has drawbacks, such as mass overlap by multiple CO2 isotopologues and contaminants, the requirement of careful sample purification, and the use of major instrumentation needing permanent installation and a high power electrical supply. Here, we report simultaneous 18O/16O, 13C/12C, and 17O/16O analyses for microgram quantities of CaCO3 using a tunable mid-infrared laser absorption spectroscopy (TILDAS) system, which has no mass overlap problem and yields high sensitivity/precision measurements on small samples, as small as 0.02 μmol of CO2 (equivalent to 2 μg of CaCO3) with standard errors of less than 0.08 ‰ for 18O/16O and 13C/12C (±0.136 ‰ and ±0.387 ‰ repeatability; n = 10). In larger samples of CO2, 0.68 μmol (or 68 μg of CaCO3), standard error is less than 0.04 ‰ for 18O/16O and 13C/12C (< ±0.1 ‰ repeatability; n = 10) and 0.03 ‰ for 17O/16O (±0.069 ‰ repeatability; n = 10). We also show, for the first time, the relationship between 17O/16O ratios measured using the TILDAS system and published δ17O values of international standard materials (NBS-18 and -19) measured by IRMS. The benchtop TILDAS system, with cryogen-free sample preparation vacuum lines for microgram quantities of carbonates, is therefore a significant advance in carbonate stable isotope ratio geochemistry and is a new alternative to conventional IRMS.

Pyrolysis behavior of thermally thick wood particles: Time-resolved characterization with laser based in-situ diagnostics

Infrared laser absorption spectroscopy (IRLAS) and laser-induced fluorescence spectroscopy (LIF) are applied in the present study for online in-situ characterization of volatiles products in the close vicinity of a single pyrolysing wood sphere. These advanced analytical techniques are combined with online measurements of temperature and mass evolutions in order to gain further insight into the complex processes occurring during slow pyrolysis of thermally thick wood particles. Three different heating rates (5, 10, 20°C/min) and two wood types (beech, pine) were used. Time-resolved absolute concentrations of the main permanent gases CO2, CO, CH4 and H2O were measured applying IRLAS. From the LIF measurements the qualitative temporal release of polycyclic aromatic hydrocarbons (PAHs) could be deduced. Different behaviors regarding the release of volatiles, temperature evolution and conversion rates were observed for both wood species, which could not be ascribed only to the different content of cellulose, hemicellulose and lignin. According to the measured volatiles evolution an enhancement of heterogeneous catalytic tar cracking seemed to be present with higher heating rates for both wood types. However, the evolution of exothermicity and PAH release differed for both wood types indicating different reaction pathways. An analysis of possible reaction pathways including secondary reactions is performed taking into account all experimental findings about the in-situ composition of the volatiles and the evolution of the PAHs as well as the exothermicity. The differences in the pyrolytic behavior of both species can be related to both the chemical and physical properties of the raw materials.