scholarly journals Different Pathways of the Formation of Highly Oxidized Multifunctional Organic Compounds (HOMs) from the Gas-Phase Ozonolysis of β-Caryophyllene

2016 ◽  
Author(s):  
Stefanie Richters ◽  
Hartmut Herrmann ◽  
Torsten Berndt
Keyword(s):  
Double Bond ◽  
Gas Phase ◽  
Organic Compounds ◽  
Atmospheric Pressure ◽  
Reaction System ◽  
Peroxy Radical ◽  
Closed Shell ◽  
Atmospheric Conditions ◽  
Reaction Products ◽  
Product Analysis

Abstract. The gas-phase mechanism of the formation of highly oxidized multifunctional organic compounds (HOMs) from the ozonolysis of β-caryophyllene was investigated in a free-jet flow system at atmospheric pressure and a temperature of 295 ± 2 K. Reaction products, mainly highly oxidized RO2 radicals, containing up to 14 oxygen atoms were detected using chemical ionization – atmospheric pressure interface – time-of-flight mass spectrometry with nitrate and acetate ionization. These highly oxidized RO2 radicals react with NO, NO2, HO22 and other RO2 radicals under atmospheric conditions forming the first-generation HOM closed-shell products. Mechanistic information on the formation of the highly oxidized RO2 radicals are based on results obtained with isotopically labeled ozone (18O3) in the ozonolysis reaction and from H/D exchange experiments of acidic H atoms in the products. The experimental findings indicate that HOM formation in this reaction system is considerably influenced by the presence of a double bond in the RO2 radicals primarily formed from the β-caryophyllene ozonolysis. Three different reaction types for HOM formation can be proposed allowing to explain the detected main products, i.e. (i) the simple autoxidation, corresponding to the repetitive reaction sequence of intramolecular H-abstraction of a RO2 radical, RO2 → QOOH, and subsequent O2 addition forming a next peroxy radical, QOOH + O2 → R'O2, (ii) an extended autoxidation mechanism additionally involving the internal reaction of a RO2 radical with a double bond forming most likely an endoperoxide, and (iii) an extended autoxidation mechanism including CO2 elimination. The individual reaction steps of the reaction types (ii) and (iii) are uncertain at the moment. From the product analysis it can be followed that the simple autoxidation mechanism accounts only for about one third of the formed HOMs. Time-dependent measurements showed that the HOM formation proceeds at a timescale of 3 s or less under the concentration regime applied here. The new reaction pathways represent an extension of the mechanistic understanding of HOM formation via autoxidation in the atmosphere, as recently discovered from laboratory investigations on monoterpene ozonolysis.

scholarly journals Different pathways of the formation of highly oxidized multifunctional organic compounds (HOMs) from the gas-phase ozonolysis of <i>β</i>-caryophyllene

2016 ◽  
Vol 16 (15) ◽  
pp. 9831-9845 ◽  
Author(s):  
Stefanie Richters ◽  
Hartmut Herrmann ◽  
Torsten Berndt
Keyword(s):  
Double Bond ◽  
Gas Phase ◽  
Organic Compounds ◽  
Atmospheric Pressure ◽  
Reaction System ◽  
Peroxy Radical ◽  
Closed Shell ◽  
Atmospheric Conditions ◽  
Reaction Products ◽  
Product Analysis

Abstract. The gas-phase mechanism of the formation of highly oxidized multifunctional organic compounds (HOMs) from the ozonolysis of β-caryophyllene was investigated in a free-jet flow system at atmospheric pressure and a temperature of 295 ± 2 K. Reaction products, mainly highly oxidized RO2 radicals containing up to 14 oxygen atoms, were detected using chemical ionization – atmospheric pressure interface – time-of-flight mass spectrometry with nitrate and acetate ionization. These highly oxidized RO2 radicals react with NO, NO2, HO2 and other RO2 radicals under atmospheric conditions forming the first-generation HOM closed-shell products. Mechanistic information on the formation of the highly oxidized RO2 radicals is based on results obtained with isotopically labelled ozone (18O3) in the ozonolysis reaction and from hydrogen/deuterium (H/D) exchange experiments of acidic H atoms in the products. The experimental findings indicate that HOM formation in this reaction system is considerably influenced by the presence of a double bond in the RO2 radicals primarily formed from the β-caryophyllene ozonolysis. Three different reaction types for HOM formation can be proposed, allowing for an explanation of the detected main products: (i) the simple autoxidation, corresponding to the repetitive reaction sequence of intramolecular H-abstraction of a RO2 radical, RO2  →  QOOH, and subsequent O2 addition, next forming a peroxy radical, QOOH + O2  →  R′O2; (ii) an extended autoxidation mechanism additionally involving the internal reaction of a RO2 radical with a double bond forming most likely an endoperoxide and (iii) an extended autoxidation mechanism including CO2 elimination. The individual reaction steps of the reaction types (ii) and (iii) are uncertain at the moment. From the product analysis it can be followed that the simple autoxidation mechanism accounts only for about one-third of the formed HOMs. Time-dependent measurements showed that the HOM formation proceeds at a timescale of 3 s or less under the concentration regime applied here. The new reaction pathways represent an extension of the mechanistic understanding of HOM formation via autoxidation in the atmosphere, as recently discovered from laboratory investigations on monoterpene ozonolysis.

Kinetics of the catalytic hydrodesulphurization reaction system; hydrogenolysis of thiophene

1980 ◽  
Vol 45 (10) ◽  
pp. 2728-2741 ◽  
Author(s):  
Pavel Fott ◽  
Petr Schneider
Keyword(s):  
Atmospheric Pressure ◽  
Active Sites ◽  
Flow Reactor ◽  
Kinetic Equations ◽  
Reaction System ◽  
Reaction Products ◽  
Molybdenum Catalyst ◽  
Cobalt Molybdenum Catalyst ◽  
Kinetics Of ◽  
Reaction Schemes

Kinetics have been studied of the reaction system taking place during the reaction of thiophene on the cobalt-molybdenum catalyst in a gradientless circulation flow reactor at 360 °C and atmospheric pressure. Butane has been found present in a small amount in the reaction products even at very low conversion. In view of this, consecutive and parallel-consecutive (triangular) reaction schemes have been proposed. In the former scheme the appearance of butane is accounted for by rate of desorption of butene being comparable with the rate of its hydrogenation. According to the latter scheme part of the butane originates from thiophene via a different route than through hydrogenation of butene. Analysis of the kinetic data has revealed that the reaction of thiophene should be considered to take place on other active sites than that of butene. Kinetic equations derived on this assumption for the consecutive and the triangular reaction schemes correlate experimental data with acceptable accuracy.

scholarly journals Modelling the evolution of organic carbon during its gas-phase tropospheric oxidation: development of an explicit model based on a self generating approach

2005 ◽  
Vol 5 (9) ◽  
pp. 2497-2517 ◽  
Author(s):  
B. Aumont ◽  
S. Szopa ◽  
S. Madronich
Keyword(s):  
Organic Carbon ◽  
Gas Phase ◽  
Organic Compounds ◽  
Parent Compound ◽  
Oxidation Products ◽  
Gradual Change ◽  
Reaction Products ◽  
Test Species ◽  
Lack Of Information ◽  
Data Processing Tool

Abstract. Organic compounds emitted in the atmosphere are oxidized in complex reaction sequences that produce a myriad of intermediates. Although the cumulative importance of these organic intermediates is widely acknowledged, there is still a critical lack of information concerning the detailed composition of the highly functionalized secondary organics in the gas and condensed phases. The evaluation of their impacts on pollution episodes, climate, and the tropospheric oxidizing capacity requires modelling tools that track the identity and reactivity of organic carbon in the various phases down to the ultimate oxidation products, CO and CO2. However, a fully detailed representation of the atmospheric transformations of organic compounds involves a very large number of intermediate species, far in excess of the number that can be reasonably written manually. This paper describes (1) the development of a data processing tool to generate the explicit gas-phase oxidation schemes of acyclic hydrocarbons and their oxidation products under tropospheric conditions and (2) the protocol used to select the reaction products and the rate constants. Results are presented using the fully explicit oxidation schemes generated for two test species: n-heptane and isoprene. Comparisons with well-established mechanisms were performed to evaluate these generated schemes. Some preliminary results describing the gradual change of organic carbon during the oxidation of a given parent compound are presented.

Perchlorosilanes and Perchlorocarbosilanes as Precursors to Silicon Carbide

2006 ◽  
Vol 911 ◽  
Author(s):  
Vladimir Sevastyanov ◽  
Yurij Ezhov ◽  
Roman Pavelko ◽  
Nikolaj Kuznetsov
Keyword(s):  
Thermal Decomposition ◽  
Silicon Carbide ◽  
Low Temperature ◽  
Gas Phase ◽  
Thermodynamic Modeling ◽  
Reaction System ◽  
Reaction Products ◽  
Gaseous Species ◽  
Phase Synthesis ◽  
Key Features

AbstractHomologues with the general stoichiometry a(SiCl4) : bSi : cC : d(SiC) are shown to be potential precursors for the low-temperature gas-phase synthesis of silicon carbide. Thermal decomposition of these precursors yields the chemically stable gaseous species SiCl4 and condensed Si, C, SiC, SiC+Si, or SiC+C. Thermodynamic modeling of the thermal decomposition of octachlorotrisilane, Si3Cl8, is used to analyze the key features of the thermolysis of perchlorosilanes with the general stoichiometry a(SiCl4) : bSi. The equilibrium compositions of reaction products in the Si3Cl8+CO system are determined. This reaction system enables low-temperature (400 – 1200 K) synthesis of silicon carbide.

scholarly journals The kinetics and mechanism of an aqueous phase isoprene reaction with hydroxyl radical

2011 ◽  
Vol 11 (15) ◽  
pp. 7399-7415 ◽  
Author(s):  
D. Huang ◽  
X. Zhang ◽  
Z. M. Chen ◽  
Y. Zhao ◽  
X. L. Shen
Keyword(s):  
Oxalic Acid ◽  
Gas Phase ◽  
Organic Compounds ◽  
Aqueous Phase ◽  
Laboratory Simulation ◽  
Potential Contribution ◽  
Phase Reaction ◽  
Oh Radical ◽  
Reaction Products ◽  
Isoprene Oxidation

Abstract. Aqueous phase chemical processes of organic compounds in the atmosphere have received increasing attention, partly due to their potential contribution to the formation of secondary organic aerosol (SOA). Here, we analyzed the aqueous OH-initiated oxidation of isoprene and its reaction products including carbonyl compounds and organic acids, regarding the acidity and temperature as in-cloudy conditions. We also performed a laboratory simulation to improve our understanding of the kinetics and mechanisms for the products of aqueous isoprene oxidation that are significant precursors of SOA; these included methacrolein (MACR), methyl vinyl ketone (MVK), methyl glyoxal (MG), and glyoxal (GL). We used a novel chemical titration method to monitor the concentration of isoprene in the aqueous phase. We used a box model to interpret the mechanistic differences between aqueous and gas phase OH radical-initiated isoprene oxidations. Our results were the first demonstration of the rate constant for the reaction between isoprene and OH radical in water, 1.2 ± 0.4) × 1010 M−1 s−1 at 283 K. Molar yields were determined based on consumed isoprene. Of note, the ratio of the yields of MVK (24.1 ± 0.8 %) to MACR (10.9 ± 1.1%) in the aqueous phase isoprene oxidation was approximately double that observed for the corresponding gas phase reaction. We hypothesized that this might be explained by a water-induced enhancement in the self-reaction of a hydroxy isoprene peroxyl radical (HOCH2C(CH3)(O2)CH = CH2) produced in the aqueous reaction. The observed yields for MG and GL were 11.4 ± 0.3 % and 3.8 ± 0.1 %, respectively. Model simulations indicated that several potential pathways may contribute to the formation of MG and GL. Finally, oxalic acid increased steadily throughout the course of the study, even after isoprene was consumed completely. The observed yield of oxalic acid was 26.2 ± 0.8 % at 6 h. The observed carbon balance accounted for ~50 % of the consumed isoprene. The presence of high-molecular-weight compounds may have accounted for a large portion of the missing carbons, but they were not quantified in this study. In summary, our work has provided experimental evidence that the availably abundant water could affect the distribution of oxygenated organic compounds produced in the oxidation of volatile organic compounds.

scholarly journals Multiday production of condensing organic aerosol mass in urban and forest outflow

2014 ◽  
Vol 14 (12) ◽  
pp. 17999-18047 ◽  
Author(s):  
J. Lee-Taylor ◽  
A. Hodzic ◽  
S. Madronich ◽  
B. Aumont ◽  
M. Camredon ◽  
...  
Keyword(s):  
Gas Phase ◽  
Organic Aerosol ◽  
Chemical Mechanism ◽  
Atmospheric Conditions ◽  
Reaction Products ◽  
Anthropogenic Aerosol ◽  
Air Masses ◽  
Aerosol Mass ◽  
Mass Increase ◽  
Radiative Characteristics

Abstract. Secondary organic aerosol (SOA) production in air masses containing either anthropogenic or biogenic (terpene-dominated) emissions is investigated using the explicit gas-phase chemical mechanism generator GECKO-A. Simulations show several-fold increases in SOA mass continuing for several days in the urban outflow, even as the initial air parcel is diluted into the regional atmosphere. The SOA mass increase in the forest outflow is more modest (∼50%) and of shorter duration (1–2 days). The production in the urban outflow stems from continuing oxidation of gas-phase precursors which persist in equilibrium with the particle phase, and can be attributed to multigenerational reaction products of both aromatics and alkanes. In particular we find large contributions from substituted maleic anhydrides and multi-substituted peroxide-bicyclic alkenes. The results show that the predicted production is a robust feature of our model even under changing atmospheric conditions, and contradict the notion that SOA undergoes little mass production beyond a short initial formation period. The results imply that anthropogenic aerosol precursors could influence the chemical and radiative characteristics of the atmosphere over an extremely wide region, and that SOA measurements near precursor sources may routinely underestimate this influence.

scholarly journals Modelling the evolution of organic carbon during its gas-phase tropospheric oxidation: development of an explicit model based on a self generating approach

2005 ◽  
Vol 5 (1) ◽  
pp. 703-754 ◽  
Author(s):  
B. Aumont ◽  
S. Szopa ◽  
S. Madronich
Keyword(s):  
Organic Carbon ◽  
Gas Phase ◽  
Organic Compounds ◽  
Parent Compound ◽  
Oxidation Products ◽  
Gradual Change ◽  
Reaction Products ◽  
Test Species ◽  
Lack Of Information ◽  
Data Processing Tool

Abstract. Organic compounds emitted in the atmosphere are oxidized in complex reaction sequences that produce a myriad of intermediates. Although the cumulative importance of these organic intermediates is widely acknowledged, there is still a critical lack of information concerning the detailed composition of the highly functionalized secondary organics in the gas and condensed phases. The evaluation of their impacts on pollution episodes, climate, and the tropospheric oxidizing capacity requires modelling tools that track the identity and reactivity of organic carbon in the various phases down to the ultimate oxidation products, CO and CO2. However, a fully detailed representation of the atmospheric transformations of organic compounds involves a very large number of intermediate species, far in excess of the number that can be reasonably written manually. This paper describes (1) the development of a data processing tool to generate the explicit gas-phase oxidation schemes of organic compounds under tropospheric conditions and (2) the protocol used to select the reaction products and the rate constants. Results are presented using the fully explicit oxidation schemes generated for two test species: n-heptane and isoprene. Comparisons with well-established mechanisms were performed to evaluate these generated schemes. Some preliminary results describing the gradual change of organic carbon during the oxidation of a given parent compound are presented.

scholarly journals Real-time detection of highly oxidized organosulfates and BSOA marker compounds during the F–BEACh 2014 field study

2016 ◽  
Author(s):  
Martin Brüggemann ◽  
Laurent Poulain ◽  
Andreas Held ◽  
Torsten Stelzer ◽  
Christoph Zuth ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Field Study ◽  
Gas Phase ◽  
Organic Compounds ◽  
Atmospheric Pressure ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Aerosol Mass ◽  
Marker Compounds ◽  
Sulfur Containing

Abstract. The chemical composition of organic aerosols was analyzed using complementary mass spectrometric techniques during a field study in Central Europe in July 2014 (Fichtelgebirge – Biogenic Emission and Aerosol Chemistry, F–BEACh 2014). Aerosols were analyzed in real-time by Aerosol Flowing Atmospheric-Pressure Afterglow Mass Spectrometry (AeroFAPA–MS), Aerosol Mass Spectrometry (AMS), and Chemical Ionization Atmospheric-Pressure interface Time-of-Flight Mass Spectrometry (CI–APiToF–MS). In addition, offline detection of acidic organic compounds was conducted by non-target screening of filter samples using High Resolution Mass Spectrometry (HRMS) in combination with Ultra-High Pressure Liquid Chromatography (UHPLC). In total, 93 acidic organic compounds were identified as characteristic contributors to the organic aerosol mass at the site. Among the carbon-, hydrogen-, oxygen-containing compounds, several common biogenic secondary organic aerosol (BSOA) marker compounds were detected. High concentrations were found for the monoterpene photooxidation products 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) and 3 carboxyheptanedioic acid, suggesting that α-/β-pinene and d-limonene oxidation products were dominating the organic aerosol fraction. In agreement, volatile organic compound (VOC) measurements showed high mixing ratios for these monoterpenes. Moreover, the high abundance of MBTCA and 3-carboxyheptanedioic acid and their concentration ratios to earlier-generation oxidation products, such as pinic acid, indicate that aged aerosol masses were present during the campaign period. HYSPLIT trajectory calculations revealed that most of the arriving air masses traveled long distances (>1,500 km) over land with high solar radiation, further supporting this hypothesis. Around 47 % of the detected compounds from the filter sample analysis were sulfur-containing, suggesting a high anthropogenic impact on biogenic emissions and their oxidation processes. Among the sulfur-containing compounds, several organosulfates, nitrooxy organosulfates, and highly oxidized organosulfates (HOOS) were unambiguously identified. In addition, correlations among HOOS classes, sulfate and highly oxidized multifunctional organic compounds (HOMs) were investigated. The results support the hypothesis of previous studies that HOOS are formed by reactions of gas-phase HOMs with particulate sulfate. Furthermore, a good agreement was observed between HOOS formation and gas-phase peroxyradical (RO2•) concentrations, measured by the CI–APiTOF–MS. This finding suggests RO2• to be either a direct or indirect precursor for HOOS. In addition, periods with high relative humidity revealed that aqueous-phase chemistry might play a major role in HOOS production.

scholarly journals Atmospheric degradation of 3-methylfuran: kinetic and products study

2011 ◽  
Vol 11 (7) ◽  
pp. 3227-3241 ◽  
Author(s):  
A. Tapia ◽  
F. Villanueva ◽  
M. S. Salgado ◽  
B. Cabañas ◽  
E. Martínez ◽  
...  
Keyword(s):  
Gas Phase ◽  
Aromatic Ring ◽  
Atmospheric Pressure ◽  
Ring Opening ◽  
Room Temperature ◽  
Rate Coefficients ◽  
Main Reaction ◽  
Phase Reaction ◽  
Reaction Products ◽  
Cl Atoms

Abstract. A study of the kinetics and products obtained from the reactions of 3-methylfuran with the main atmospheric oxidants has been performed. The rate coefficients for the gas-phase reaction of 3-methylfuran with OH and NO3 radicals have been determined at room temperature and atmospheric pressure (air and N2 as bath gases), using a relative method with different experimental techniques. The rate coefficients obtained for these reactions were (in units cm3 molecule−1 s−1) kOH = (1.13 ± 0.22) × 10−10 and kNO3 = (1.26 ± 0.18) × 10−11. Products from the reaction of 3-methylfuran with OH, NO3 and Cl atoms in the absence and in the presence of NO have also been determined. The main reaction products obtained were chlorinated methylfuranones and hydroxy-methylfuranones in the reaction of 3-methylfuran with Cl atoms, 2-methylbutenedial, 3-methyl-2,5-furanodione and hydroxy-methylfuranones in the reaction of 3-methylfuran with OH and NO3 radicals and also nitrated compounds in the reaction with NO3 radicals. The results indicate that, in all cases, the main reaction path is the addition to the double bond of the aromatic ring followed by ring opening in the case of OH and NO3 radicals. The formation of 3-furaldehyde and hydroxy-methylfuranones (in the reactions of 3-methylfuran with Cl atoms and NO3 radicals) confirmed the H-atom abstraction from the methyl group and from the aromatic ring, respectively. This study represents the first product determination for Cl atoms and NO3 radicals in reactions with 3-methylfuran. The reaction mechanisms and atmospheric implications of the reactions under consideration are also discussed.

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