scholarly journals Formation of highly oxygenated organic molecules from chlorine atom initiated oxidation of alpha-pinene

2019 ◽  
Author(s):  
Yonghong Wang ◽  
Matthieu Riva ◽  
Hongbin Xie ◽  
Liine Heikkinen ◽  
Simon Schallhart ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Organic Aerosol ◽  
Heterogeneous Reactions ◽  
Peroxy Radicals ◽  
Chlorine Atoms ◽  
Uncertainty Range ◽  
Nitryl Chloride ◽  
Alpha Pinene ◽  
Calibration Methods ◽  
Substantial Uncertainty

Abstract. Highly oxygenated organic molecules (HOMs) from atmospheric oxidation of alpha-pinene can irreversibly condense to particles and contribute to secondary organic aerosol (SOA) formation. Recently, the formation of nitryl chloride (ClNO2) from heterogeneous reactions, followed by its subsequent photolysis is suggested to be an important source of chlorine atoms in many parts of the atmosphere. However, the oxidation of monoterpenes such as alpha-pinene by chlorine atoms has received very little attention, and the ability of this reaction to form HOM is completely unstudied. Here, chamber experiments were conducted with alpha-pinene and chlorine under low and high nitrogen oxide (NOx) conditions. A NO3-based CI-APi-TOF was used to measure HOM products. Clear distributions of monomers with 9–10 carbon atoms and dimers with 18–20 carbon atoms were observed under low NOx conditions. With increased concentration of NOx within the chamber, the formation of dimers was suppressed due to the reactions of peroxy radicals with NO. We estimated the HOM yields from chlorine-initiated oxidation of alpha-pinene under low-NOx conditions to be around 1.8 %, though with a substantial uncertainty range (0.8–4 %) due to lack of suitable calibration methods. Corresponding yields at high NOx could not be determined because of concurrent ozonolysis reactions. Our study demonstrates that chlorine atoms also initiated oxidation of alpha-pinene and yields low volatility organic compounds.

scholarly journals Formation of highly oxygenated organic molecules from chlorine-atom-initiated oxidation of alpha-pinene

2020 ◽  
Vol 20 (8) ◽  
pp. 5145-5155 ◽  
Author(s):  
Yonghong Wang ◽  
Matthieu Riva ◽  
Hongbin Xie ◽  
Liine Heikkinen ◽  
Simon Schallhart ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Organic Aerosol ◽  
Heterogeneous Reactions ◽  
Peroxy Radicals ◽  
Chlorine Atoms ◽  
Uncertainty Range ◽  
Nitryl Chloride ◽  
Alpha Pinene ◽  
Calibration Methods ◽  
Substantial Uncertainty

Abstract. Highly oxygenated organic molecules (HOMs) from atmospheric oxidation of alpha-pinene can irreversibly condense to particles and contribute to secondary organic aerosol (SOA) formation. Recently, the formation of nitryl chloride (ClNO2) from heterogeneous reactions, followed by its subsequent photolysis, is suggested to be an important source of chlorine atoms in many parts of the atmosphere. However, the oxidation of monoterpenes such as alpha-pinene by chlorine atoms has received very little attention, and the ability of this reaction to form HOMs is completely unstudied. Here, chamber experiments were conducted with alpha-pinene and chlorine under low- and high-nitrogen-oxide (NOx, NOx=NO+NO2) conditions. A nitrate-based CI-APi-ToF (chemical ionization–atmospheric pressure interface–time of flight) mass spectrometer was used to measure HOM products. Clear distributions of monomers with 9–10 carbon atoms and dimers with 18–20 carbon atoms were observed under low-NOx conditions. With increased concentration of NOx within the chamber, the formation of dimers was suppressed due to the reactions of peroxy radicals with NO. We estimated the HOM yields from chlorine-initiated oxidation of alpha-pinene under low-NOx conditions to be around 1.8 %, though with a substantial uncertainty range (0.8 %–4 %) due to lack of suitable calibration methods. Corresponding yields at high NOx could not be determined because of concurrent ozonolysis reactions. Our study demonstrates that also the oxidation of alpha-pinene by chlorine atoms and yield low-volatility organic compounds.

scholarly journals Peroxy Radical Chemistry and the Volatility Basis Set

2019 ◽  
Author(s):  
Meredith Schervish ◽  
Neil M. Donahue
Keyword(s):  
Temperature Dependence ◽  
Gas Phase ◽  
Organic Molecules ◽  
Peroxy Radical ◽  
Organic Aerosol ◽  
Basis Set ◽  
Strong Temperature Dependence ◽  
Peroxy Radicals ◽  
Cross Reactions ◽  
Oxidation Of Organics

Abstract. Gas-phase auto-oxidation of organics can generate highly-oxygenated organic molecules (HOMs) and thus increase secondary organic aerosol production and enable new-particle formation. Here we present a new implementation of the Volatility Basis Set (VBS) that explicitly resolves peroxy radicals (RO2) formed via auto-oxidation. The model includes a strong temperature dependence for auto oxidation as well as explicit termination of RO2, including reactions with NO, HO2, and other RO2. The RO2 cross reactions can produce dimers (ROOR). We explore the temperature and NOx dependence of this chemistry, showing that temperature strongly influences the intrinsic volatility distribution and that NO can suppress auto-oxidation under conditions typically found in the atmosphere.

The effect of NOx on formation of Highly Oxidized Multifunctional Molecules and SOA formation in photochemical system of α-pinene and β-pinene

2020 ◽  
Author(s):  
Sungah Kang ◽  
Thomas Mentel ◽  
Iida Pullinen ◽  
Monika Springer ◽  
Einhard Kleist ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Organic Aerosol ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Peroxy Radicals ◽  
Vapor Pressures ◽  
Alkoxy Radicals ◽  
Alkyl Radicals ◽  
Degree Of Oxidation ◽  
Multifunctional Molecules

<p>Highly oxygenated organic molecules (HOM) are formed in the atmosphere by autoxidation, i.e. peroxy radicals can undergo H-shift followed by O<sub>2</sub> addition. A sequence of these very fast steps leads to highly oxygenated peroxy radicals (HOM-RO<sub>2</sub>) and finally to stable termination products with O/C>1.<br>As other RO<sub>2</sub>, HOM-RO<sub>2</sub> are terminated by reactions with RO<sub>2</sub>, HO<sub>2</sub> and NO<sub>x</sub> and in addition form efficiently stable accretion products. In this study, three noticeable effects on HOM formation were found by introducing NO<sub>x</sub> in the photochemical system of monoterpenes. One effect is formation of highly oxygenated organic nitrates (HOM-ON) with sufficiently low vapor pressures allowing significant contributios to SOA formation. The second one is dimer suppression, because of competing dimer pathway (HOM-RO<sub>2</sub>·+ RO<sub>2</sub>·) and organic nitrate pathway (HOM-RO<sub>2</sub>·+ NO<sub>x</sub>). Thirdly, the reaction between peroxy radicals and NO increases alkoxy radicals in the system. The fragmentation of alkoxy radicals produces volatile compounds that should result in decrease of SOA yield. However, the effect of fragmentation is offset: alkoxy radicals also undergo H-shifts that produce alkyl radicals and after O<sub>2</sub> addition peroxy radicals, that eventually are higher oxygenated.</p><p>Because of their low volatility, HOM play a crucial role in new particle formation and secondary organic aerosol (SOA) formation. Suppression of dimers and increased degree of oxidation of the HOM monomer play together with the result of only a small reduction of the SOA yields.</p>

scholarly journals Effect of temperature on the formation of Highly-oxygenated Organic Molecules (HOM) from alpha-pinene ozonolysis

2018 ◽  
Author(s):  
Lauriane L. J. Quéléver ◽  
Kasper Kristensen ◽  
Louise Jensen ◽  
Bernadette Rosati ◽  
Ricky Teiwes ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Peroxy Radical ◽  
Effect Of Temperature ◽  
Strong Temperature Dependence ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Experimental Conditions ◽  
Mass Spectral ◽  
Alpha Pinene ◽  
Lower Temperature

Abstract. Highly-oxygenated Organic Molecules (HOM) are important contributors to Secondary Organic Aerosol (SOA) and New-Particle Formation (NPF) in the boreal atmosphere. This newly discovered class of molecules is efficiently formed from atmospheric oxidation of biogenic volatile organic compounds (VOC), such as monoterpenes, through a process called autoxidation. This process, in which peroxy-radical intermediates isomerize to allow addition of molecular oxygen, is expected to be highly temperature-dependent. Here, we studied the dynamics of HOM formation during alpha-pinene ozonolysis experiments performed at three different temperatures, 20 °C, 0 °C and −15 °C, in the Aarhus University Research on Aerosol (AURA) chamber. We found that the HOM formation, under our experimental conditions (50 ppb alpha-pinene, 100 ppb ozone), decreased considerably as temperature decreased, with molar yields dropping by around a factor of 50 when experiments were performed at 0 °C, compared to 20 °C. At −15 °C, the HOM signals were already close to the detection limit of the nitrate-based Chemical Ionization Atmospheric Pressure interface Time Of Flight (CI-APi-TOF) mass spectrometer used for measuring gas-phase HOM. Surprisingly, very little difference was seen in the mass spectral distribution of the HOM molecules of interest at 0 °C and 20 °C, with e.g. the ratios between the typical HOM products C10H14O7, C10H14O9, and C10H14O11 remaining fairly constant. The more oxidized species have undergone more isomerization steps, yet, at lower temperature, they did not decrease more than the less oxidized species. One possible explanation is be that the rate-limiting step forming these HOM occurs before the products become oxygenated enough to be detected by our CI-APi-TOF (i.e. typically seven or more oxygen atoms). The strong temperature dependence of HOM formation was observed under temperatures highly relevant for the boreal forest, but the exact magnitude of this effect in the atmosphere will be much more complex: the fate of peroxy-radicals is a competition between autoxidation (influenced by temperature and VOC type) and bimolecular termination pathways (influenced mainly by concentration of reaction partners). While the temperature influence is likely smaller in the boreal atmosphere than in our chamber, the magnitude and complexity of this effect clearly deserves more consideration in future studies in order to estimate the ultimate role of HOM on SOA and NPF under different atmospheric conditions.

scholarly journals Effect of temperature on the formation of highly oxygenated organic molecules (HOMs) from alpha-pinene ozonolysis

2019 ◽  
Vol 19 (11) ◽  
pp. 7609-7625 ◽  
Author(s):  
Lauriane L. J. Quéléver ◽  
Kasper Kristensen ◽  
Louise Normann Jensen ◽  
Bernadette Rosati ◽  
Ricky Teiwes ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Peroxy Radical ◽  
Effect Of Temperature ◽  
Strong Temperature Dependence ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Experimental Conditions ◽  
Alpha Pinene ◽  
Different Temperatures ◽  
Lower Temperature

Abstract. Highly oxygenated organic molecules (HOMs) are important contributors to secondary organic aerosol (SOA) and new-particle formation (NPF) in the boreal atmosphere. This newly discovered class of molecules is efficiently formed from atmospheric oxidation of biogenic volatile organic compounds (VOCs), such as monoterpenes, through a process called autoxidation. This process, in which peroxy-radical intermediates isomerize to allow addition of molecular oxygen, is expected to be highly temperature-dependent. Here, we studied the dynamics of HOM formation during α-pinene ozonolysis experiments performed at three different temperatures, 20, 0 and −15 ∘C, in the Aarhus University Research on Aerosol (AURA) chamber. We found that the HOM formation, under our experimental conditions (50 ppb α-pinene and 100 ppb ozone), decreased considerably at lower temperature, with molar yields dropping by around a factor of 50 when experiments were performed at 0 ∘C, compared to 20 ∘C. At −15 ∘C, the HOM signals were already close to the detection limit of the nitrate-based chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer used for measuring gas-phase HOMs. Surprisingly, comparing spectra measured at 0 and 20 ∘C, ratios between HOMs of different oxidation levels, e.g., the typical HOM products C10H14O7, C10H14O9, and C10H14O11, changed considerably less than the total HOM yields. More oxidized species have undergone more isomerization steps; yet, at lower temperature, they did not decrease more than the less oxidized species. One possible explanation is that the primary rate-limiting steps forming these HOMs occur before the products become oxygenated enough to be detected by our CI-APi-TOF (i.e., typically seven or more oxygen atoms). The strong temperature dependence of HOM formation was observed under temperatures highly relevant to the boreal forest, but the exact magnitude of this effect in the atmosphere will be much more complex: the fate of peroxy radicals is a competition between autoxidation (influenced by temperature and VOC type) and bimolecular termination pathways (influenced mainly by concentration of reaction partners). While the temperature influence is likely smaller in the boreal atmosphere than in our chamber, both the magnitude and complexity of this effect clearly deserve more consideration in future studies in order to estimate the ultimate role of HOMs on SOA and NPF under different atmospheric conditions.

scholarly journals Constraining condensed-phase formation kinetics of secondary organic aerosol components from isoprene epoxydiols

2016 ◽  
Vol 16 (3) ◽  
pp. 1245-1254 ◽  
Author(s):  
T. P. Riedel ◽  
Y.-H. Lin ◽  
Z. Zhang ◽  
K. Chu ◽  
J. A. Thornton ◽  
...  
Keyword(s):  
Aqueous Phase ◽  
Atmospheric Aerosols ◽  
Rate Constants ◽  
Reaction Rate ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Heterogeneous Reactions ◽  
Model Calculations ◽  
Reaction Rate Constants ◽  
Aerosol Mass

Abstract. Isomeric epoxydiols from isoprene photooxidation (IEPOX) have been shown to produce substantial amounts of secondary organic aerosol (SOA) mass and are therefore considered a major isoprene-derived SOA precursor. Heterogeneous reactions of IEPOX on atmospheric aerosols form various aerosol-phase components or "tracers" that contribute to the SOA mass burden. A limited number of the reaction rate constants for these acid-catalyzed aqueous-phase tracer formation reactions have been constrained through bulk laboratory measurements. We have designed a chemical box model with multiple experimental constraints to explicitly simulate gas- and aqueous-phase reactions during chamber experiments of SOA growth from IEPOX uptake onto acidic sulfate aerosol. The model is constrained by measurements of the IEPOX reactive uptake coefficient, IEPOX and aerosol chamber wall losses, chamber-measured aerosol mass and surface area concentrations, aerosol thermodynamic model calculations, and offline filter-based measurements of SOA tracers. By requiring the model output to match the SOA growth and offline filter measurements collected during the chamber experiments, we derive estimates of the tracer formation reaction rate constants that have not yet been measured or estimated for bulk solutions.

scholarly journals CRI-HOM: A novel chemical mechanism for simulating Highly Oxygenated Organic Molecules (HOMs) in global chemistry-aerosol-climate models

2020 ◽  
Author(s):  
James Weber ◽  
Alexander Archibald ◽  
Paul Griffiths ◽  
Scott Archer-Nicholls ◽  
Torsten Berndt ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Radiative Forcing ◽  
Organic Molecules ◽  
Climate Models ◽  
Global Climate Models ◽  
Chemical Mechanism ◽  
Atmospheric Composition ◽  
Climate Modelling ◽  
Particle Nucleation ◽  
Peroxy Radicals

Abstract. We present here results from a new mechanism, CRI-HOM, which we have developed to simulate the formation of highly oxygenated organic molecules (HOMs) from the gas phase oxidation of α-pinene, one of the most widely emitted BVOCs by mass. This concise scheme adds 12 species and 66 reactions to the Common Representative Intermediates (CRI) mechanism v2.2 Reduction 5 and enables the representation of semi-explicit HOM treatment suitable for long term global chemistry- aerosol-climate modelling, within a comprehensive tropospheric chemical mechanism. The key features of the new mechanism are (i) representation of the autoxidation of peroxy radicals from the hydroxyl radical and ozone initiated reactions of α-pinene, (ii) formation of multiple generations of peroxy radicals, (iii) formation of accretion products (dimers) and (iv) isoprene-driven suppression of accretion product formation, as observed in experiments. The mechanism has been constructed through optimisation against a series of flow tube laboratory experiments. The mechanism predicts a HOM yield of 4–6 % under conditions of low to moderate NOx, in line with experimental observations, and reproduces qualitatively the decline in HOM yield and concentration at higher NOx. The mechanism gives a HOM yield that also increases with temperature, in line with observations, and our mechanism compares favourably to some of the limited observations of [HOM] observed in the boreal forest in Finland and in the south east USA. The reproduction of isoprene-driven suppression of HOMs is a key step forward as it enables global climate models to capture the interaction between the major BVOC species, along with the potential climatic feedbacks. This suppression is demonstrated when the mechanism is used to simulate atmospheric profiles over the boreal forest and rainforest; different isoprene concentrations result in different [HOM] distributions, illustrating the importance of BVOC interactions in atmospheric composition and climate. Finally particle nucleation rates calculated from [HOM] in present day and pre- industrial atmospheres suggest that sulphuric acid free nucleation can compete effectively with other nucleation pathways in the boreal forest, particularly in the pre-industrial, with important implications for the aerosol budget and radiative forcing.

scholarly journals Volatility and hygroscopicity of aging secondary organic aerosol in a smog chamber

2011 ◽  
Vol 11 (3) ◽  
pp. 7423-7467 ◽  
Author(s):  
T. Tritscher ◽  
J. Dommen ◽  
P. F. DeCarlo ◽  
P. B. Barmet ◽  
A. P. Praplan ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Organic Aerosol ◽  
Heterogeneous Reactions ◽  
Physical Parameters ◽  
Oh Radicals ◽  
Smog Chamber ◽  
Chemical Aging ◽  
Aerosol Mass ◽  
Gas Phase Oxidation ◽  
Substantial Change

Abstract. The evolution of secondary organic aerosols (SOA) during (photo-)chemical aging processes was investigated in a smog chamber. SOA from 10–40 ppb α-pinene was formed during ozonolysis followed by aging with OH radicals. The particles' volatility and hygroscopicity (expressed as volume fraction remaining (VFR) and hygroscopicity parameter κ) were measured with a volatility and hygroscopicity tandem differential mobility analyzer (V/H-TDMA). These measurements were used as sensitive physical parameters to reveal the possible mechanisms responsible for the chemical changes in the SOA composition during aging: A change of VFR and/or κ during processing of atmospheric aerosol may occur either by addition of SOA mass (by condensation) or by an exchange of molecules in the SOA by other molecules with different properties. The former process increases the SOA mass by definition, while the latter keeps the SOA mass roughly constant and may occur either by heterogeneous reactions on the surface of the SOA particles, by homogeneous reactions like oligomerization or by an evaporation – gas-phase oxidation – recondensation cycle. Thus, when there is a substantial change in the aerosol mass with time, the condensation mechanism may be assumed to be dominant, while, when the mass stays roughly constant the exchange mechanism is likely to be dominant, a process termed ripening here. Depending on the phase of the experiment, an O3 mediated condensation, O3 mediated ripening, OH mediated condensation, and OH mediated ripening could be distinguished. During the O3 mediated condensation the particles volatility decreased (increasing VFR) while the hygroscopicity increased. Thereafter, in the course of O3 mediated ripening volatility continued to decrease, but hygroscopicity stayed roughly constant. After exposing the SOA to OH radicals an OH mediated condensation started with a significant increase of SOA mass. Concurrently, hygroscopicity and volatility increased. This phase was then followed by an OH mediated ripening with a decrease of volatility.

scholarly journals Constraining condensed-phase formation kinetics of secondary organic aerosol components from isoprene epoxydiols

2015 ◽  
Vol 15 (20) ◽  
pp. 28289-28316 ◽  
Author(s):  
T. P. Riedel ◽  
Y.-H. Lin ◽  
Z. Zhang ◽  
K. Chu ◽  
J. A. Thornton ◽  
...  
Keyword(s):  
Aqueous Phase ◽  
Atmospheric Aerosols ◽  
Rate Constants ◽  
Reaction Rate ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Heterogeneous Reactions ◽  
Model Calculations ◽  
Reaction Rate Constants ◽  
Aerosol Mass

Abstract. Isomeric epoxydiols from isoprene photooxidation (IEPOX) have been shown to produce substantial amounts of secondary organic aerosol (SOA) mass and are therefore considered a major isoprene-derived SOA precursor. Heterogeneous reactions of IEPOX on atmospheric aerosols form various aerosol-phase components or "tracers" that contribute to the SOA mass burden. A limited number of the reaction rate constants for these acid-catalyzed aqueous-phase tracer formation reactions have been constrained through bulk laboratory measurements. We have designed a chemical box model with multiple experimental constraints to explicitly simulate gas- and aqueous-phase reactions during chamber experiments of SOA growth from IEPOX uptake onto acidic sulfate aerosol. The model is constrained by measurements of the IEPOX reactive uptake coefficient, IEPOX and aerosol chamber wall-losses, chamber-measured aerosol mass and surface area concentrations, aerosol thermodynamic model calculations, and offline filter-based measurements of SOA tracers. By requiring the model output to match the SOA growth and offline filter measurements collected during the chamber experiments, we derive estimates of the tracer formation reaction rate constants that have not yet been measured or estimated for bulk solutions.

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