scholarly journals Highly oxygenated organic molecules produced by the oxidation of benzene and toluene in a wide range of OH exposure and NO<sub><i>x</i></sub> conditions

2021 ◽  
Vol 21 (15) ◽  
pp. 12005-12019
Author(s):  
Xi Cheng ◽  
Qi Chen ◽  
Yong Jie Li ◽  
Yan Zheng ◽  
Keren Liao ◽  
...  
Keyword(s):  
Organic Molecules ◽  
Product Distribution ◽  
Experimental Conditions ◽  
Effective Lifetime ◽  
Product Distributions ◽  
Wide Range ◽  
Multifunctional Products ◽  
The Impact ◽  
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, the 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 that multigeneration 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. More oxygenated products present in our study than in previous flow tube studies, highlighting the impact of experimental conditions on product distributions. 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 peroxyacyl nitrates, 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 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 Effect of NO<sub><i>x</i></sub> on 1,3,5-trimethylbenzene (TMB) oxidation product distribution and particle formation

2019 ◽  
Vol 19 (23) ◽  
pp. 15073-15086 ◽  
Author(s):  
Epameinondas Tsiligiannis ◽  
Julia Hammes ◽  
Christian Mark Salvador ◽  
Thomas F. Mentel ◽  
Mattias Hallquist
Keyword(s):  
Urban Areas ◽  
Organic Molecules ◽  
Flow Reactor ◽  
Organic Aerosol ◽  
Product Distribution ◽  
Particle Formation ◽  
Product Distributions ◽  
Tropospheric Aerosol ◽  
Volatile Organic ◽  
Free Environment

Abstract. Secondary organic aerosol (SOA) represents a significant fraction of the tropospheric aerosol and its precursors are volatile organic compounds (VOCs). Anthropogenic VOCs (AVOC) dominate the VOC budget in many urban areas with 1,3,5-trimethylbenzene (TMB) being among the most reactive aromatic AVOCs. TMB formed highly oxygenated organic molecules (HOMs) in an NOx-free environment, which could contribute to new particle formation (NPF) depending on oxidation conditions where elevated OH oxidation enhanced particle formation. The experiments were performed in an oxidation flow reactor, the Go:PAM unit, under controlled OH oxidation conditions. By addition of NOx to the system we investigated the effect of NOx on particle formation and on the product distribution. We show that the formation of HOMs, and especially HOM accretion products, strongly varies with NOx conditions. We observe a suppression of HOM and particle formation with increasing NOx/ΔTMB ratio and an increase in the formation of organonitrates (ONs) mostly at the expense of HOM accretion products. We propose reaction mechanisms and pathways that explain the formation and observed product distributions with respect to oxidation conditions. We hypothesise that, based on our findings from TMB oxidation studies, aromatic AVOCs may not contribute significantly to NPF under typical NOx/AVOC conditions found in urban atmospheres.

Reactions of Alkyl Halides in Fused Salt Media

1971 ◽  
Vol 49 (1) ◽  
pp. 1-6 ◽  
Author(s):  
R. A. Bailey ◽  
S. F. Prest
Keyword(s):  
Organic Molecules ◽  
Product Distribution ◽  
Exchange Reactions ◽  
Cyclization Reactions ◽  
Composition Effects ◽  
Carbonium Ion ◽  
Product Distributions ◽  
Halide Exchange ◽  
Melt Composition ◽  
Acid Character

Passage of C1 to C5 haloalkanes through SnCl2–KCl melts results in halide exchange reactions, alkene formation, and rearrangement (including cyclization) reactions of the organic molecules. Relative reactivities, product distributions and melt composition effects are consistent with a carbonium ion mechanism in which the melt functions as a halide ion acceptor. Some control of product distribution by choice of Lewis acid character of the melt seems possible.

scholarly journals Experimental Guidelines for Studies Designed to Investigate the Impact of Antioxidant Supplementation on Exercise Performance

2010 ◽  
Vol 20 (1) ◽  
pp. 2-14 ◽  
Author(s):  
Scott K. Powers ◽  
Ashley J. Smuder ◽  
Andreas N. Kavazis ◽  
Matthew B. Hudson
Keyword(s):  
Oxidative Stress ◽  
Oxidative Damage ◽  
Antioxidant Capacity ◽  
Exercise Performance ◽  
Human Performance ◽  
Experimental Situation ◽  
Redox Balance ◽  
Experimental Conditions ◽  
Wide Range ◽  
The Impact

Research interest in the effects of antioxidants on exercise-induced oxidative stress and human performance continues to grow as new scientists enter this field. Consequently, there is a need to establish an acceptable set of criteria for monitoring antioxidant capacity and oxidative damage in tissues. Numerous reports have described a wide range of assays to detect both antioxidant capacity and oxidative damage to biomolecules, but many techniques are not appropriate in all experimental conditions. Here, the authors present guidelines for selecting and interpreting methods that can be used by scientists to investigate the impact of antioxidants on both exercise performance and the redox status of tissues. Moreover, these guidelines will be useful for reviewers who are assigned the task of evaluating studies on this topic. The set of guidelines contained in this report is not designed to be a strict set of rules, because often the appropriate procedures depend on the question being addressed and the experimental model. Furthermore, because no individual assay is guaranteed to be the most appropriate in every experimental situation, the authors strongly recommend using multiple assays to verify a change in biomarkers of oxidative stress or redox balance.

scholarly journals Estimation of Critical Uncertainty Sources in Discharge Measurements using Controlled Experimental Conditions

2018 ◽  
Vol 40 ◽  
pp. 06046
Author(s):  
Dongsu Kim ◽  
Aurélien Despax ◽  
Marian Muste ◽  
Jérôme Le Coz
Keyword(s):  
Acoustic Doppler Velocimeter ◽  
Experimental Facility ◽  
Experimental Conditions ◽  
Uncertainty Sources ◽  
Wide Range ◽  
Discharge Estimation ◽  
Sampling Duration ◽  
The Impact ◽  
Natural Scale

Providing experimental results along with associated uncertainties is essential not only for ensuring confidence in the quality of the final results but also for guiding improved instrument design and the protocols for measurement acquisition. Moreover, if the uncertainty analysis is conducted in a controlled manner and over a wide range for the measured variables its results can serve as a decision-making aid in conducting new experiments. This paper provides three examples of end-to-end assessments of the impact of uncertainty sources involved in the discharge estimation in open channels using point velocities measured with Acoustic Doppler Velocimeter. The analyzed uncertainty sources are: a) the sampling duration for velocity measurement, b) the number of points in the verticals, and, c) the number of verticals across the measurement cross-section. The raw data for the uncertainty estimations were acquired at the KICT River Experiment Center (South Korea), an experimental facility designed for facilitiating quasi natural-scale experiments. The three sources of uncertainties are assembled in practical visualization means that can be used for planning the acquisition of new experiments with similar instruments.

scholarly journals Modelling the formation and composition of secondary organic aerosol from α- and β-pinene ozonolysis using MCM v3

2004 ◽  
Vol 4 (3) ◽  
pp. 2905-2948 ◽  
Author(s):  
M. E. Jenkin
Keyword(s):  
Secondary Organic Aerosol ◽  
Experimental Studies ◽  
Organic Aerosol ◽  
Chemical Mechanism ◽  
Oh Radicals ◽  
Product Distributions ◽  
Wide Range ◽  
Partitioning Coefficients ◽  
Detailed Composition ◽  
Multifunctional Products

Abstract. The formation and detailed composition of secondary organic aerosol (SOA) from the gas phase ozonolysis of α- and β-pinene has been simulated using the Master Chemical Mechanism version 3 (MCM v3), coupled with a representation of gas-to-aerosol transfer of semivolatile and involatile oxygenated products. A kinetics representation, based on equilibrium absorptive partitioning of ca. 200 semivolatile products, was found to provide an acceptable description of the final mass concentrations observed in a number of reported laboratory and chamber experiments, provided partitioning coefficients were increased by about two orders of magnitude over those defined on the basis of estimated vapour pressures. This adjustment is believed to be due, at least partially, to the effect of condensed phase association reactions of the partitioning products. Even with this adjustment, the simulated initial formation of SOA was delayed relative to that observed, implying the requirement for the formation of species of much lower volatility to initiate SOA formation. The inclusion of a simplified representation of the formation and gas-to-aerosol transfer of involatile dimers of 22 bi- and multifunctional carboxylic acids (in addition to the absorptive partitioning mechanism) allowed a much improved description of SOA formation for a wide range of conditions. The simulated SOA composition recreates certain features of the product distributions observed in a number of experimental studies, but implies an important role for multifunctional products containing hydroperoxy groups (i.e. hydroperoxides). This is particularly the case for experiments in which 2-butanol is used to scavenge OH radicals, because [HO2]/[RO2] ratios are elevated in such systems. The optimized mechanism is used to calculate SOA yields from α- and β-pinene ozonolysis in the presence and absence of OH scavengers, and as a function of temperature.

scholarly journals Modelling the formation and composition of secondary organic aerosol from α- and β-pinene ozonolysis using MCM v3

2004 ◽  
Vol 4 (7) ◽  
pp. 1741-1757 ◽  
Author(s):  
M. E. Jenkin
Keyword(s):  
Secondary Organic Aerosol ◽  
Experimental Studies ◽  
Organic Aerosol ◽  
Chemical Mechanism ◽  
Oh Radicals ◽  
Product Distributions ◽  
Wide Range ◽  
Partitioning Coefficients ◽  
Detailed Composition ◽  
Multifunctional Products

Abstract. The formation and detailed composition of secondary organic aerosol (SOA) from the gas phase ozonolysis of α- and β-pinene has been simulated using the Master Chemical Mechanism version 3 (MCM v3), coupled with a representation of gas-to-aerosol transfer of semivolatile and involatile oxygenated products. A kinetics representation, based on equilibrium absorptive partitioning of ca. 200 semivolatile products, was found to provide an acceptable description of the final mass concentrations observed in a number of reported laboratory and chamber experiments, provided partitioning coefficients were increased by about two orders of magnitude over those defined on the basis of estimated vapour pressures. This adjustment is believed to be due, at least partially, to the effect of condensed phase association reactions of the partitioning products. Even with this adjustment, the simulated initial formation of SOA was delayed relative to that observed, implying the requirement for the formation of species of much lower volatility to initiate SOA formation. The inclusion of a simplified representation of the formation and gas-to-aerosol transfer of involatile dimers of 22 bi- and multifunctional carboxylic acids (in addition to the absorptive partitioning mechanism) allowed a much improved description of SOA formation for a wide range of conditions. The simulated SOA composition recreates certain features of the product distributions observed in a number of experimental studies, but implies an important role for multifunctional products containing hydroperoxy groups (i.e. hydroperoxides). This is particularly the case for experiments in which 2-butanol is used to scavenge OH radicals, because [HO2]/[RO2] ratios are elevated in such systems. The optimized mechanism is used to calculate SOA yields from α- and β-pinene ozonolysis in the presence and absence of OH scavengers, and as a function of temperature.

scholarly journals Global-Scale Metabolomic Profiling of Human Hair for Simultaneous Monitoring of Endogenous Metabolome, Short- and Long-Term Exposome

2021 ◽  
Vol 9 ◽  
Author(s):  
Ying Chen ◽  
Jian Guo ◽  
Shipei Xing ◽  
Huaxu Yu ◽  
Tao Huan
Keyword(s):  
High Performance ◽  
High Resolution Mass Spectrometry ◽  
Global Scale ◽  
Short Term ◽  
Experimental Conditions ◽  
Hair Samples ◽  
Wide Range ◽  
Endogenous Metabolites ◽  
The Impact

Hair is a unique biological matrix that adsorbs short-term exposures (e. g., environmental contaminants and personal care products) on its surface and also embeds endogenous metabolites and long-term exposures in its matrix. In this work, we developed an untargeted metabolomics workflow to profile both temporal exposure chemicals and endogenous metabolites in the same hair sample. This analytical workflow begins with the extraction of short-term exposures from hair surfaces through washing. Further development of mechanical homogenization extracts endogenous metabolites and long-term exposures from the cleaned hair. Both solutions of hair wash and hair extract were analyzed using ultra-high-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HRMS)-based metabolomics for global-scale metabolic profiling. After analysis, raw data were processed using bioinformatic programs recently developed specifically for exposome research. Using optimized experimental conditions, we detected a total of 10,005 and 9,584 metabolic features from hair wash and extraction samples, respectively. Among them, 274 and 276 features can be definitively confirmed by MS2 spectral matching against spectral library, and an additional 3,356 and 3,079 features were tentatively confirmed as biotransformation metabolites. To demonstrate the performance of our hair metabolomics, we collected hair samples from three female volunteers and tested their hair metabolic changes before and after a 2-day exposure exercise. Our results show that 645 features from wash and 89 features from extract were significantly changed from the 2-day exposure. Altogether, this work provides a novel analytical approach to study the hair metabolome and exposome at a global scale, which can be implemented in a wide range of biological applications for a deeper understanding of the impact of environmental and genetic factors on human health.

scholarly journals Effect of NO<sub>x</sub> on 1,3,5-trimethylbenzene (TMB) oxidation product distribution and particle formation

2019 ◽  
Author(s):  
Julia Hammes ◽  
Epameinondas Tsiligiannis ◽  
Thomas F. Mentel ◽  
Mattias Hallquist
Keyword(s):  
Urban Areas ◽  
Organic Molecules ◽  
Flow Reactor ◽  
Organic Aerosol ◽  
Product Distribution ◽  
Particle Formation ◽  
Product Distributions ◽  
Tropospheric Aerosol ◽  
Volatile Organic ◽  
Free Environment

Abstract. Secondary organic aerosol (SOA) represents a significant fraction of the tropospheric aerosol and its precursors are volatile organic compounds (VOC). Anthropogenic VOCs (AVOC) dominate the VOC budget in many urban areas with 1,3,5-trimethylbenzene (TMB) being among the most reactive aromatic AVOCs. TMB formed highly oxygenated organic molecules (HOM) in NOx free environment, which could contribute to new particle formation (NPF) depending on oxidation conditions were elevated OH oxidation enhanced particle formation. The experiments were performed in an oxidation flow reactor, the Go : PAM unit, under controlled OH oxidation conditions. By addition of NOx to the system we investigated the effect of NOx on particle formation and on the product distribution. We show that the formation of HOM and especially HOM accretion products, strongly varies with NOx conditions. We observe a suppression of HOM and particle formation with increasing NOx / ΔTMB and an increase in the formation of organonitrates (ON) mostly at the expense of HOM accretion products. We propose reaction mechanisms/pathways that explain the formation and observed product distributions with respect to oxidation conditions. We hypothesize that, based on our findings from TMB oxidation studies, aromatic AVOCs may not contribute significantly to NPF under typical NOx / AVOC conditions found in urban atmospheres.

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