scholarly journals Enhancement of atmospheric H<sub>2</sub>SO<sub>4</sub> / H<sub>2</sub>O nucleation: organic oxidation products versus amines

2014 ◽  
Vol 14 (2) ◽  
pp. 751-764 ◽  
Author(s):  
T. Berndt ◽  
M. Sipilä ◽  
F. Stratmann ◽  
T. Petäjä ◽  
J. Vanhanen ◽  
...  
Keyword(s):  
First Generation ◽  
Oxidation Products ◽  
Oh Radicals ◽  
Flow Tube ◽  
Experimental Conditions ◽  
Criegee Intermediates ◽  
Wide Range ◽  
Independent Process ◽  
Oxidant Production ◽  
Organic Oxidation

Abstract. Atmospheric H2SO4 / H2O nucleation influencing effects have been studied in the flow tube IfT-LFT (Institute for Tropospheric Research – Laminar Flow Tube) at 293 ± 0.5 K and a pressure of 1 bar using synthetic air as the carrier gas. The presence of a possible background amine concentration in the order of 107–108 molecule cm−3 throughout the experiments has to be taken into account. In a first set of investigations, ozonolysis of olefins (tetramethylethylene, 1-methyl-cyclohexene, α-pinene and limonene) for close to atmospheric concentrations, served as the source of OH radicals and possibly other oxidants initiating H2SO4 formation starting from SO2. The oxidant generation is inevitably associated with the formation of organic oxidation products arising from the parent olefins. These products (first generation mainly) showed no clear effect on the number of nucleated particles within a wide range of experimental conditions for H2SO4 concentrations higher than ~107 molecule cm−3. Also the early growth process of the nucleated particles was not significantly influenced by the organic oxidation products in line with the expected growth by organic products using literature data. An additional, H2SO4-independent process of particle (nano-CN) formation was observed in the case of α-pinene and limonene ozonolysis for H2SO4 concentrations smaller than ~107 molecule cm−3. Furthermore, the findings confirm the appearance of an additional oxidant for SO2 beside OH radicals, very likely stabilized Criegee Intermediates (sCI). A second set of experiments has been performed in the presence of added amines in the concentrations range of a few 107–1010 molecule cm−3 applying photolytic OH radical generation for H2SO4 production without addition of other organics. All amines showed significant nucleation enhancement with increasing efficiency in the order pyridine < aniline < dimethylamine < trimethylamine. This result supports the idea of H2SO4 cluster stabilization by amines due to strong H2SO4↔amine interactions. On the other hand, this study indicates that for organic oxidation products (in presence of the possible amine background as stated) a distinct H2SO4 / H2O nucleation enhancement can be due to increased H2SO4 formation caused by additional organic oxidant production (sCI) rather than by stabilization of H2SO4 clusters due to H2SO4↔organics interactions.

scholarly journals Enhancement of atmospheric H<sub>2</sub>SO<sub>4</sub>/H<sub>2</sub>O nucleation: organic oxidation products versus amines

2013 ◽  
Vol 13 (6) ◽  
pp. 16301-16335 ◽  
Author(s):  
T. Berndt ◽  
M. Sipilä ◽  
F. Stratmann ◽  
T. Petäjä ◽  
J. Vanhanen ◽  
...  
Keyword(s):  
Oxidation Products ◽  
Radical Scavenger ◽  
Oh Radicals ◽  
Oh Radical ◽  
Flow Tube ◽  
Experimental Conditions ◽  
Wide Range ◽  
Nucleation Mechanisms ◽  
Comparison Of The Results ◽  
Organic Oxidation

Abstract. Atmospheric H2SO4/H2O nucleation influencing effects have been studied in the flow tube IfT-LFT (Institute for Tropospheric Research – Laminar Flow Tube) at 293 ± 0.5 K and a pressure of 1 bar using synthetic air as the carrier gas. The presence of a possible background amine concentration in the order of 107–108 molecule cm−3 throughout the experiments has to be taken into account. In a first set of investigations, ozonolysis of olefins (tetramethylethylene, 1-methyl-cyclohexene, α-pinene and limonene) for close to atmospheric concentrations, served as the source of OH radicals and possibly other oxidants initiating H2SO4 formation starting from SO2. The oxidant generation is inevitably associated with the formation of a series of organic oxidation products arising from the parent olefins. These products (first generation mainly) showed no clear effect on the number of nucleated particles within a wide range of experimental conditions for H2SO4 concentrations higher than ~107 molecule cm−3. A comparison of the results of two different particle counters (50% cut-off size: about 1.5 nm or 2.5–3 nm) suggested that the early growth process of the nucleated particles was not significantly influenced by the organic oxidation products. An additional, H2SO4-independent process of particle (nano-CN) formation was observed in the case of α-pinene and limonene ozonolysis for H2SO4 concentrations smaller than ~10 7 molecule cm−3. Furthermore, the findings confirm the existence of an additional oxidant for SO2 beside OH radicals, very likely stabilized Criegee Intermediate (sCI). In the case of the ozonolysis of tetramethylethylene, the H2SO4 measurements in the absence and presence of an OH radical scavenger were well described by modelling using recently obtained kinetic data for the sCI reactivity in this system. A second set of experiments has been performed in the presence of added amines (trimethylamine, dimethylamine, aniline and pyridine) in the concentration range of a few 107–1010 molecule cm−3. Here, photolytic OH radical generation was applied for H2SO4 production with no addition of other organics. All amines showed a significant nucleation enhancement with increasing efficiency in the order pyridine < aniline < dimethylamine < trimethylamine. This result supports the idea of H2SO4 cluster stabilization by amines due to strong H2SO4 &amp;leftrightarrow; amine interactions. On the other hand, this study reveals that for organic oxidation products (in presence of the possible amine background as stated) a distinct H2SO4/H2O nucleation enhancement can be due to increased H2SO4 formation caused by additional organic oxidant production (sCI) rather than by stabilization of H2SO4 clusters due to H2SO4 &amp;leftrightarrow; organics interactions. However, because the molecular composition of nucleating clusters was not measured, the role of any background substances, unavoidably present in any system, to experimental data remains unclear. Also the experimental conditions do not cover fully the range of atmospheric observations, e.g., the concentration of precursor vapours represents rather the upper end of the atmospheric range. More experimental work is needed before definite conclusions about the nucleation mechanisms in the atmosphere can be drawn.

scholarly journals Highly Oxygenated Organic Molecules Produced by the Oxidation of Benzene and Toluene in a Wide Range of OH Exposure and NO<sub>x</sub> Conditions

2021 ◽  
Author(s):  
Xi Cheng ◽  
Qi Chen ◽  
Yong Jie Li ◽  
Yan Zheng ◽  
Keren Liao ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Product Distribution ◽  
Flow Tube ◽  
Experimental Conditions ◽  
Effective Lifetime ◽  
Wide Range ◽  
Volatile Organic ◽  
Multifunctional Products ◽  
Oxidation Of Benzene ◽  
Oxygenated Products

Abstract. Oxidation of aromatic volatile organic compounds (VOCs) leads to the formation of tropospheric ozone and secondary organic aerosol, for which gaseous oxygenated products are important intermediates. We show herein experimental results of highly oxygenated organic molecules (HOMs) produced by the oxidation of benzene and toluene in a wide range of OH exposure and NOx conditions. The results suggest multi-generation OH oxidation plays an important role in the product distribution, which likely proceeds more preferably via H subtraction than OH addition for early-generation products from light aromatics. Our experimental conditions promote the formation of more oxygenated products than previous flow-tube studies. The formation of dimeric products however was suppressed and might be unfavorable under conditions of high OH exposure and low NOx in toluene oxidation. Under high-NOx conditions, nitrogen-containing multifunctional products are formed, while the formation of other HOMs is suppressed. Products containing two nitrogen atoms become more important as the NOx level increases, and the concentrations of these compounds depend significantly on NO2. The highly oxygenated nitrogen-containing products might be peroxyacylnitrates, implying a prolonged effective lifetime of RO2 that facilitates regional pollution. Our results call for further investigation on the roles of high-NO2 conditions in the oxidation of aromatic VOCs.

scholarly journals Photo-oxidation of pinonaldehyde at low NO<sub>x</sub>: from chemistry to organic aerosol formation

2013 ◽  
Vol 13 (6) ◽  
pp. 3227-3236 ◽  
Author(s):  
H. J. Chacon-Madrid ◽  
K. M. Henry ◽  
N. M. Donahue
Keyword(s):  
First Generation ◽  
Single Species ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Photochemical Oxidation ◽  
Oh Radicals ◽  
General Tendency ◽  
Aerosol Formation ◽  
Uv Illumination ◽  
Terpene Oxidation

Abstract. Pinonaldehyde oxidation by OH radicals under low-NOx conditions produces significant secondary organic aerosol (SOA) mass yields. Under concurrent UV illumination, mass yields are lower than high-NOx yields published earlier by our group. However, when OH radicals are produced via dark ozonolysis the SOA mass yields are comparable at high and low NOx. Because pinonaldehyde is a major first-generation gas-phase product of α-pinene oxidation by either ozone or OH radicals, its potential to form SOA serves as a molecular counterpoint to bulk SOA aging experiments involving SOA formed from α-pinene. Both the general tendency for aging reactions to produce more SOA and the sensitivity of the low-NOx products to UV photolysis observed in the bulk clearly occur for this single species as well. Photochemical oxidation of pinonaldehye and analogous first-generation terpene oxidation products are potentially a significant source of additional SOA in biogenically influenced air masses.

scholarly journals Photo-oxidation of pinonaldehyde at low NO<sub>x</sub>: from chemistry to organic aerosol formation

2012 ◽  
Vol 12 (3) ◽  
pp. 7727-7752 ◽  
Author(s):  
H. J. Chacon-Madrid ◽  
K. M. Henry ◽  
N. M. Donahue
Keyword(s):  
First Generation ◽  
Single Species ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Photochemical Oxidation ◽  
Oh Radicals ◽  
General Tendency ◽  
Aerosol Formation ◽  
Uv Illumination ◽  
Terpene Oxidation

Abstract. Pinonaldehyde oxidation by OH radicals under low-NOx conditions produces significant secondary organic aerosol (SOA) mass yields. Under concurrent UV illumination, mass yields are lower than high-NOx yields published earlier by our group. However, when OH radicals are produced via dark ozonolysis the SOA mass yields are comparable at high and low NOx. Because pinonaldehyde is a major first-generation gas-phase product of α-pinene oxidation by either ozone or OH radicals, its potential to form SOA serves as a molecular counterpoint to bulk SOA aging experiments involving SOA formed from α-pinene. Both the general tendency for aging reactions to produce more SOA and the sensitivity of the low-NOx products to UV photolysis observed in the bulk clearly occur for this single species as well. Photochemical oxidation of pinonaldehye and analogous first-generation terpene oxidation products are potentially a significant source of additional SOA in biogenically influenced air masses.

scholarly journals The role of radical chemistry in the product formation from nitrate radical initiated gas-phase oxidation of isoprene

2021 ◽  
Author(s):  
Philip T. M. Carlsson ◽  
Luc Vereecken ◽  
Anna Novelli ◽  
François Bernard ◽  
Birger Bohn ◽  
...  
Keyword(s):  
Gas Phase ◽  
First Generation ◽  
Product Distribution ◽  
Chem Phys ◽  
Oxidation Products ◽  
Rate Coefficients ◽  
Peroxy Radicals ◽  
Model Calculations ◽  
Alkoxy Radicals ◽  
Wide Range

&lt;p&gt;Experiments at atmospherically relevant conditions were performed in the simulation chamber SAPHIR, investigating the reaction of isoprene with NO&lt;sub&gt;3&lt;/sub&gt; and its subsequent oxidation. Due to the production of NO&lt;sub&gt;3&lt;/sub&gt; from the reaction of NO&lt;sub&gt;2&lt;/sub&gt; with O&lt;sub&gt;3&lt;/sub&gt; as well as the formation of OH in subsequent reactions, the reactions of isoprene with O&lt;sub&gt;3&lt;/sub&gt; and OH were estimated to contribute up to 15% of the total isoprene consumption each in these experiments. The ratio of RO&lt;sub&gt;2&lt;/sub&gt; to HO&lt;sub&gt;2&lt;/sub&gt; concentrations was varied by changing the reactant concentrations, which modifies the product distribution from bimolecular reactions of the nitrated RO&lt;sub&gt;2&lt;/sub&gt;. The reaction with HO&lt;sub&gt;2&lt;/sub&gt; or NO&lt;sub&gt;3&lt;/sub&gt; was found to be the main bimolecular loss process for the RO&lt;sub&gt;2&lt;/sub&gt; radicals under all conditions examined.&lt;/p&gt;&lt;p&gt;Yields of the first-generation isoprene oxygenated nitrates as well as the sum of methyl vinyl ketone (MVK) and methacrolein (MACR) were determined by high resolution proton mass spectrometry using the Vocus PTR-TOF. The experimental time series of these products are compared to model calculations based on the MCM v3.3.1,&lt;sup&gt;1&lt;/sup&gt; the isoprene mechanism as published by Wennberg &lt;em&gt;et al.&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt; and the newly developed FZJ-NO&lt;sub&gt;3&lt;/sub&gt;-isoprene mechanism,&lt;sup&gt;3&lt;/sup&gt; which incorporates theory-based rate coefficients for a wide range of reactions.&lt;/p&gt;&lt;p&gt;Among other changes, the FZJ-NO&lt;sub&gt;3&lt;/sub&gt;-isoprene mechanism contains a novel fast oxidation route through the epoxidation of alkoxy radicals, originating from the formation of nitrated peroxy radicals. This inhibits the formation of MVK and MACR from the NO&lt;sub&gt;3&lt;/sub&gt;-initiated oxidation of isoprene to practically zero, which agrees with the observations from chamber experiments. In addition, the FZJ-NO&lt;sub&gt;3&lt;/sub&gt;-isoprene mechanism increases the level of agreement for the main first-generation oxygenated nitrates.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;1&lt;/sup&gt; M. E. Jenkin, J. C. Young and A. R. Rickard, The MCM v3.3.1 degradation scheme for isoprene, &lt;em&gt;Atmospheric Chem. Phys.&lt;/em&gt;, 2015, &lt;strong&gt;15&lt;/strong&gt;, 11433&amp;#8211;11459.&lt;/p&gt;&lt;p&gt;&lt;sup&gt;2&lt;/sup&gt; P. O. Wennberg &lt;em&gt;at al.&lt;/em&gt;, Gas-Phase Reactions of Isoprene and Its Major Oxidation Products, &lt;em&gt;Chem. Rev.&lt;/em&gt;, 2018, &lt;strong&gt;118&lt;/strong&gt;, 3337&amp;#8211;3390.&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;3&lt;/sup&gt; L. Vereecken &lt;em&gt;et al.&lt;/em&gt;, Theoretical and experimental study of peroxy and alkoxy radicals in the NO3-initiated oxidation of isoprene, &lt;em&gt;Phys. Chem. Chem. Phys.&lt;/em&gt;, submitted.&lt;/p&gt;

Strongly Coupled Redox-Linked Conformational Switching at the Active Site of the Non-Heme Iron-Dependent Dioxygenase, TauD

2019 ◽  
Author(s):  
Christopher John ◽  
Greg M. Swain ◽  
Robert P. Hausinger ◽  
Denis A. Proshlyakov
Keyword(s):  
Active Site ◽  
Structural Model ◽  
Heme Iron ◽  
Chemical Transformations ◽  
Experimental Conditions ◽  
Strongly Coupled ◽  
Non Heme Iron ◽  
Reversible Redox ◽  
Wide Range ◽  
Complex Structural

2-Oxoglutarate (2OG)-dependent dioxygenases catalyze C-H activation while performing a wide range of chemical transformations. In contrast to their heme analogues, non-heme iron centers afford greater structural flexibility with important implications for their diverse catalytic mechanisms. We characterize an <i>in situ</i> structural model of the putative transient ferric intermediate of 2OG:taurine dioxygenase (TauD) by using a combination of spectroelectrochemical and semi-empirical computational methods, demonstrating that the Fe (III/II) transition involves a substantial, fully reversible, redox-linked conformational change at the active site. This rearrangement alters the apparent redox potential of the active site between -127 mV for reduction of the ferric state and 171 mV for oxidation of the ferrous state of the 2OG-Fe-TauD complex. Structural perturbations exhibit limited sensitivity to mediator concentrations and potential pulse duration. Similar changes were observed in the Fe-TauD and taurine-2OG-Fe-TauD complexes, thus attributing the reorganization to the protein moiety rather than the cosubstrates. Redox difference infrared spectra indicate a reorganization of the protein backbone in addition to the involvement of carboxylate and histidine ligands. Quantitative modeling of the transient redox response using two alternative reaction schemes across a variety of experimental conditions strongly supports the proposal for intrinsic protein reorganization as the origin of the experimental observations.

Introduction

2018 ◽  
Author(s):  
Anna-Maria Hartmann
Keyword(s):  
Sixteenth Century ◽  
Early Modern ◽  
Literary History ◽  
First Generation ◽  
Early Modern England ◽  
Related Material ◽  
Wide Range ◽  
The World ◽  
Early English

Mythographies were books that collected, explained, and interpreted myth-related material. Extremely popular during the Renaissance, these works appealed to a wide range of readers. While the European mythographies of the sixteenth century have been utilized by scholars, the short, early English mythographies, written from 1577 to 1647, have puzzled critics. The first generation of English mythographers did not, as has been suggested, try to compete with their Italian predecessors. Instead, they made mythographies into rhetorical instruments designed to intervene in topical debates outside the world of classical learning. Because English mythographers brought mythology to bear on a variety of contemporary issues, they unfold a lively and historically well-defined picture of the roles myth was made to play in early modern England. Exploring these mythographies can contribute to previous insights into myth in the Renaissance offered by studies of iconography, literary history, allegory, and myth theory.

scholarly journals Low-Energy Electron Damage to Condensed-Phase DNA and Its Constituents

2021 ◽  
Vol 22 (15) ◽  
pp. 7879
Author(s):  
Yingxia Gao ◽  
Yi Zheng ◽  
Léon Sanche
Keyword(s):  
Condensed Phase ◽  
Genetic Material ◽  
High Energy ◽  
Dna Lesions ◽  
Low Energy ◽  
Experimental Investigations ◽  
Experimental Conditions ◽  
Strand Breaks ◽  
Sequence Of Events ◽  
Wide Range

The complex physical and chemical reactions between the large number of low-energy (0–30 eV) electrons (LEEs) released by high energy radiation interacting with genetic material can lead to the formation of various DNA lesions such as crosslinks, single strand breaks, base modifications, and cleavage, as well as double strand breaks and other cluster damages. When crosslinks and cluster damages cannot be repaired by the cell, they can cause genetic loss of information, mutations, apoptosis, and promote genomic instability. Through the efforts of many research groups in the past two decades, the study of the interaction between LEEs and DNA under different experimental conditions has unveiled some of the main mechanisms responsible for these damages. In the present review, we focus on experimental investigations in the condensed phase that range from fundamental DNA constituents to oligonucleotides, synthetic duplex DNA, and bacterial (i.e., plasmid) DNA. These targets were irradiated either with LEEs from a monoenergetic-electron or photoelectron source, as sub-monolayer, monolayer, or multilayer films and within clusters or water solutions. Each type of experiment is briefly described, and the observed DNA damages are reported, along with the proposed mechanisms. Defining the role of LEEs within the sequence of events leading to radiobiological lesions contributes to our understanding of the action of radiation on living organisms, over a wide range of initial radiation energies. Applications of the interaction of LEEs with DNA to radiotherapy are briefly summarized.

scholarly journals Review of the Upright Balance Assessment Based on the Force Plate

2021 ◽  
Vol 18 (5) ◽  
pp. 2696
Author(s):  
Baoliang Chen ◽  
Peng Liu ◽  
Feiyun Xiao ◽  
Zhengshi Liu ◽  
Yong Wang
Keyword(s):  
Postural Balance ◽  
Force Plate ◽  
Assessment Method ◽  
Balance Assessment ◽  
Experimental Conditions ◽  
Methodological Research ◽  
Assessment Tests ◽  
Wide Range ◽  
Foot Posture ◽  
Plate System

Quantitative assessment is crucial for the evaluation of human postural balance. The force plate system is the key quantitative balance assessment method. The purpose of this study is to review the important concepts in balance assessment and analyze the experimental conditions, parameter variables, and application scope based on force plate technology. As there is a wide range of balance assessment tests and a variety of commercial force plate systems to choose from, there is room for further improvement of the test details and evaluation variables of the balance assessment. The recommendations presented in this article are the foundation and key part of the postural balance assessment; these recommendations focus on the type of force plate, the subject’s foot posture, and the choice of assessment variables, which further enriches the content of posturography. In order to promote a more reasonable balance assessment method based on force plates, further methodological research and a stronger consensus are still needed.

scholarly journals Computational Fluid Dynamics Modeling of Rotating Annular VUV/UV Photoreactor for Water Treatment

Processes ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 79
Author(s):  
Minghan Luo ◽  
Wenjie Xu ◽  
Xiaorong Kang ◽  
Keqiang Ding ◽  
Taeseop Jeong
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Water Treatment ◽  
Cfd Modeling ◽  
Flow Mode ◽  
Oh Radicals ◽  
Dynamics Modeling ◽  
Rotational Movement ◽  
Contaminant Degradation ◽  
Wide Range

The ultraviolet photochemical degradation process is widely recognized as a low-cost, environmentally friendly, and sustainable technology for water treatment. This study integrated computational fluid dynamics (CFD) and a photoreactive kinetic model to investigate the effects of flow characteristics on the contaminant degradation performance of a rotating annular photoreactor with a vacuum-UV (VUV)/UV process performed in continuous flow mode. The results demonstrated that the introduced fluid remained in intensive rotational movement inside the reactor for a wide range of inflow rates, and the rotational movement was enhanced with increasing influent speed within the studied velocity range. The CFD modeling results were consistent with the experimental abatement of methylene blue (MB), although the model slightly overestimated MB degradation because it did not fully account for the consumption of OH radicals from byproducts generated in the MB decomposition processes. The OH radical generation and contaminant degradation efficiency of the VUV/UV process showed strong correlation with the mixing level in a photoreactor, which confirmed the promising potential of the developed rotating annular VUV reactor in water treatment.

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