Peroxy Radical Processes and Product Formation in the OH Radical-Initiated Oxidation of α-Pinene for Near-Atmospheric Conditions

2021 ◽  
Author(s):  
Torsten Berndt
Keyword(s):  
Peroxy Radical ◽  
Product Formation ◽  
Oh Radical ◽  
Atmospheric Conditions ◽  
Radical Processes

New pathways of the reaction of OH radicals with dimethyl sulfide based on CH3SCH2O2 isomerization

2020 ◽  
Author(s):  
Torsten Berndt ◽  
Wiebke Scholz ◽  
Bernhard Mentler ◽  
Lukas Fischer ◽  
Erik Hans Hoffmann ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Dimethyl Sulfide ◽  
Peroxy Radical ◽  
Product Formation ◽  
Experimental Investigations ◽  
Oh Radicals ◽  
Atmospheric Conditions ◽  
Free Jet ◽  
Isomerization Process ◽  
Efficient Detection

<p>Dimethyl sulfide (DMS), produced by marine organisms, represents the most abundant, biogenic sulfur emission into the Earth´s atmosphere. The gas-phase degradation of DMS is mainly initiated by the reaction with the OH radical forming first CH<sub>3</sub>SCH<sub>2</sub>O<sub>2</sub> radicals from the dominant H-abstraction channel. A fast CH<sub>3</sub>SCH<sub>2</sub>O<sub>2</sub> isomerization process was proposed as a result of quantum chemical calculations. In the present study, experimental investigations on the product formation from OH + DMS have been conducted in a free-jet flow system at 295 ± 2 K and 1 bar air. Very efficient detection of CH<sub>3</sub>SCH<sub>2</sub>O<sub>2</sub> isomerization products has been achieved by iodide-CI-APi-TOF measurements allowing to run the reaction for close to atmospheric conditions. It is experimentally shown that the CH<sub>3</sub>SCH<sub>2</sub>O<sub>2</sub> radicals undergo a two-step isomerization process finally forming a product consistent with the formula HOOCH<sub>2</sub>SCHO. The isomerization process is accompanied by OH recycling. The rate-limiting first isomerization step, CH<sub>3</sub>SCH<sub>2</sub>O<sub>2</sub> → CH<sub>2</sub>SCH<sub>2</sub>OOH proceeds with k = (0.23 ± 0.12) s<sup>-1</sup> at 295 ± 2 K. Competing bimolecular CH<sub>3</sub>SCH<sub>2</sub>O<sub>2</sub> reactions with NO, HO<sub>2</sub> or RO<sub>2</sub> radicals are less important for trace-gas conditions over the oceans.  Results of atmospheric chemistry simulations demonstrate the predominance (≥95%) of CH<sub>3</sub>SCH<sub>2</sub>O<sub>2</sub> isomerization. The rapid peroxy radical isomerization, not yet considered in models, substantially changes the understanding of DMS´s degradation processes in the atmosphere.</p>

scholarly journals Influence of Gaseous Environment on Reaction Behavior and Phase Formation in Ti/2B Reactive Multilayer Foils

2012 ◽  
Vol 1405 ◽  
Author(s):  
Robert V. Reeves ◽  
Mark A. Rodriguez ◽  
Eric D. Jones ◽  
David P. Adams
Keyword(s):  
High Speed ◽  
Ambient Pressure ◽  
Product Formation ◽  
Atmospheric Conditions ◽  
Bilayer Thickness ◽  
X Ray Diffraction ◽  
High Speed Imaging ◽  
Reaction Behavior ◽  
Gaseous Environment ◽  
Sputter Deposited

ABSTRACTThe effects of surrounding gaseous environment on the reaction behaviors and product formation for sputter-deposited Ti/2B reactive multilayers are reported. With the surrounding environment set to different air pressures, from atmospheric conditions to 10-4 Torr, Ti/2B samples were reacted in a self-propagating mode, and the average reaction wave velocities were determined through high-speed imaging. Propagation speeds for 3.0 μm-thick multilayers were in the range of 10.89 to 0.05 m/s depending on bilayer thickness (i.e., reactant layer periodicity) and ambient pressure. X-ray diffraction analysis showed that single-phase TiB2 forms within multilayers that have small bilayer thickness. Multilayers that have a large bilayer thickness developed a mixture of TiB2, TiB and TiO2.

scholarly journals Intercomparison of peroxy radical measurements obtained at atmospheric conditions by laser-induced fluorescence and electron spin resonance spectroscopy

2009 ◽  
Vol 2 (1) ◽  
pp. 55-64 ◽  
Author(s):  
H. Fuchs ◽  
T. Brauers ◽  
R. Häseler ◽  
F. Holland ◽  
D. Mihelcic ◽  
...  
Keyword(s):  
Electron Spin Resonance ◽  
Electron Spin ◽  
Peroxy Radical ◽  
High Sensitivity ◽  
Chemical Conversion ◽  
Laser Induced Fluorescence ◽  
Resonance Spectroscopy ◽  
Atmospheric Conditions ◽  
Data Set ◽  
Spin Resonance

Abstract. Measurements of hydroperoxy radical (HO2) and organic peroxy radical (RO2) concentrations were performed by two different techniques in the atmospheric simulation chamber SAPHIR in Jülich, Germany. The first technique was the well-established Matrix Isolation Electron Spin Resonance (MIESR), which provides absolute measurements with a time resolution of 30 min and high accuracy (10%, 2 σ). The other technique, ROxLIF, has been newly developed. It is based on the selective chemical conversion of ROx radicals (HO2 and RO2) to OH, which is detected with high sensitivity by laser-induced fluorescence (LIF). ROxLIF is calibrated by quantitative photolysis of water vapor at 185 nm and provides ambient measurements at a temporal resolution of 1 min and accuracy of 20% (2 σ). The measurements of HO2 and RO2 obtained by the two techniques were compared for two types of atmospheric simulation experiments. In one experiment, HO2 and CH3O2 radicals were produced by photooxidation of methane in air at tropospheric conditions. In the second experiment, HO2 and C2H5O2 were produced by ozonolysis of 1-butene in air at dark conditions. The radical concentrations were within the range of 16 to 100 pptv for HO2 and 12 to 45 pptv for RO2. Good agreement was found in the comparison of the ROxLIF and MIESR measurements within their combined experimental uncertainties. Linear regressions to the combined data set yield slopes of 1.02±0.13 (1 σ) for RO2 and 0.98±0.08 (1 σ) for HO2 without significant offsets. The results confirm the calibration of the ROxLIF instrument and demonstrate that it can be applied with good accuracy for measurements of atmospheric peroxy radical concentrations.

Importance of isomerization reactions for the OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

2020 ◽  
Author(s):  
Anna Novelli ◽  
Luc Vereecken ◽  
Birger Bohn ◽  
Hans-Peter Dorn ◽  
Georgios Gkatzelis ◽  
...  
Keyword(s):  
Oh Radicals ◽  
Oh Radical ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Unimolecular Reactions ◽  
Model Calculations ◽  
Hydrogen Shift ◽  
Wide Range ◽  
Regeneration Efficiency ◽  
Simulation Chamber

<p>Theoretical, laboratory and chamber studies have shown fast regeneration of hydroxyl radical (OH) in the photochemistry of isoprene largely due to previously disregarded unimolecular reactions which were previously thought not to be important under atmospheric conditions. Based on early field measurements, nearly complete regeneration was hypothesized for a wide range of tropospheric conditions, including areas such as the rainforest where slow regeneration of OH radicals is expected due to low concentrations of nitric oxide (NO). In this work the OH regeneration in the isoprene oxidation is directly quantified for the first time through experiments covering a wide range of atmospheric conditions (i.e. NO between 0.15 and 2 ppbv and temperature between 25 and 41°C) in the atmospheric simulation chamber SAPHIR. These conditions cover remote areas partially influenced by anthropogenic NO emissions, giving a regeneration efficiency of OH close to one, and areas like the Amazonian rainforest with very low NO, resulting in a surprisingly high regeneration efficiency of 0.5, i.e. a factor of 2 to 3 higher than explainable in the absence of unimolecular reactions. The measured radical concentrations were compared to model calculations and the best agreement was observed when at least 50% of the total loss of isoprene peroxy radicals conformers (weighted by their abundance) occurs via isomerization reactions for NO lower than 0.2 parts per billion (ppbv). For these levels of NO, up to 50% of the OH radicals are regenerated from the products of the 1,6 α-hydroxy-hydrogen shift (1,6-H shift) of Z-δ-RO<sub>2 </sub>radicals through photolysis of an unsaturated hydroperoxy aldehyde (HPALD) and/or through the fast aldehyde hydrogen shift (rate constant ~10 s<sup>-1</sup> at 300K) in di-hydroperoxy carbonyl peroxy radicals (di-HPCARP-RO<sub>2</sub>), depending on their relative yield. The agreement between all measured and modelled trace gases (hydroxyl, hydroperoxy and organic peroxy radicals, carbon monoxide and the sum of methyl vinyl ketone, methacrolein and hydroxyl hydroperoxides) is nearly independent on the adopted yield of HPALD and di-HPCARP-RO<sub>2</sub> as both degrade relatively fast (< 1 h), forming OH radical and CO among other products. Taking into consideration this and earlier isoprene studies, considerable uncertainties remain on the oxygenated products distribution, which affect radical levels and organic aerosol downwind of unpolluted isoprene dominated regions.</p>

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.

Relative rate coefficient measurements of OH radical reactions with (Z)-2-hexen-1-ol and (E)-3-hexen-1-ol under simulated atmospheric conditions

2014 ◽  
Vol 85 ◽  
pp. 92-98 ◽  
Author(s):  
Silvina A. Peirone ◽  
Javier A. Barrera ◽  
Raúl A. Taccone ◽  
Pablo M. Cometto ◽  
Silvia I. Lane
Keyword(s):  
Rate Coefficient ◽  
Relative Rate ◽  
Radical Reactions ◽  
Oh Radical ◽  
Atmospheric Conditions

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 &amp;rightarrow; QOOH, and subsequent O2 addition forming a next peroxy radical, QOOH + O2 &amp;rightarrow; 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.

Extent of H-atom abstraction from the reaction of the OH radical with 1-butene under atmospheric conditions

1985 ◽  
Vol 17 (7) ◽  
pp. 725-734 ◽  
Author(s):  
Roger Atkinson ◽  
Ernesto C. Tuazon ◽  
William P. L. Carter
Keyword(s):  
Oh Radical ◽  
Atmospheric Conditions

scholarly journals Investigation of the reaction of ozone with isoprene, methacrolein and methyl vinyl ketone using the HELIOS chamber

2017 ◽  
Vol 200 ◽  
pp. 289-311 ◽  
Author(s):  
Yangang Ren ◽  
Benoit Grosselin ◽  
Véronique Daële ◽  
Abdelwahid Mellouki
Keyword(s):  
Gas Phase ◽  
Organic Aerosol ◽  
Vinyl Ketone ◽  
Methyl Vinyl Ketone ◽  
Radical Scavenger ◽  
Oh Radical ◽  
Atmospheric Conditions ◽  
Experimental Conditions ◽  
Methyl Vinyl ◽  
Analytical Equipment

The rate constants for the ozonolysis of isoprene (ISO), methacrolein (MACR) and methyl vinyl ketone (MVK) have been measured using the newly built large volume atmospheric simulation chamber at CNRS-Orleans (France), HELIOS (Chambre de simulation atmosphérique à irradiation naturelle d’Orléans). The OH radical yields from the ozonolysis of isoprene, MACR and MVK have also been determined, as well as the gas phase stable products and their yields. The secondary organic aerosol yield for the ozonolysis of isoprene has been tentatively measured in the presence and absence of an OH radical scavenger. The measurements were performed under different experimental conditions with and without adding cyclohexane (cHX) as an OH radical scavenger. All experiments have been conducted at 760 torr of purified dry air (RH < 1%) and ambient temperature (T = 281–295 K). The data obtained are discussed and compared with those from the literature. The use of the HELIOS facility and its associated analytical equipment enables the derivation of kinetic parameters as well as mechanistic information under near realistic atmospheric conditions.

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