scholarly journals Oxygenated products formed from OH-initiated reactions of trimethylbenzene: autoxidation and accretion

2020 ◽  
Vol 20 (15) ◽  
pp. 9563-9579
Author(s):  
Yuwei Wang ◽  
Archit Mehra ◽  
Jordan E. Krechmer ◽  
Gan Yang ◽  
Xiaoyu Hu ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Flow Reactor ◽  
Time Of Flight ◽  
Oxidation Products ◽  
Urban Atmosphere ◽  
Reaction Pathways ◽  
Peroxy Radicals ◽  
Flight Mass Spectrometer

Abstract. Gas-phase oxidation pathways and products of anthropogenic volatile organic compounds (VOCs), mainly aromatics, are the subject of intensive research, with attention paid to their contributions to secondary organic aerosol (SOA) formation and potentially new particle formation (NPF) in the urban atmosphere. In this study, a series of OH-initiated oxidation experiments of trimethylbenzene (TMB, C9H12) including 1,2,4-TMB, 1,3,5-TMB, 1,2,3-TMB, and 1,2,4-(methyl-D3)-TMBs (C9H9D3) were investigated in an oxidation flow reactor (OFR) in the absence and presence of NOx. Products were measured using a suite of state-of-the-art instruments, i.e. a nitrate-based chemical ionization–atmospheric pressure interface time-of-flight mass spectrometer (nitrate CI-APi-TOF), an iodide-adduct chemical ionization time-of-flight mass spectrometer (iodide CI-TOF) equipped with a Filter Inlet for Gases and AEROsols (FIGAERO), and a Vocus proton-transfer-reaction mass spectrometer (Vocus PTR). A large number of C9 products with 1–11 oxygen atoms and C18 products presumably formed from dimerization of C9 peroxy radicals were observed, hinting at the extensive existence of autoxidation and accretion reaction pathways in the OH-initiated oxidation reactions of TMBs. Oxidation products of 1,2,4-(methyl-D3)-TMBs with deuterium atoms in different methyl substituents were then used as a molecular basis to propose potential autoxidation reaction pathways. Accretion of C9 peroxy radicals is the most significant for aromatics with meta-substituents and the least for aromatics with ortho-substituents if the number and size of substituted groups are identical. The presence of NOx would suppress the formation of highly oxygenated molecules (HOMs) of C18 and enhance the formation of organonitrates and even dinitrate organic compounds. Our results show that the oxidation products of TMB are much more diverse and could be more oxygenated than the current mechanisms predict.

scholarly journals Oxygenated products formed from OH-initiated reactions of trimethylbenzene: Autoxidation and accretion

2020 ◽  
Author(s):  
Yuwei Wang ◽  
Archit Mehra ◽  
Jordan E. Krechmer ◽  
Gan Yang ◽  
Xiaoyu Hu ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Flow Reactor ◽  
Time Of Flight ◽  
Oxidation Products ◽  
Urban Atmosphere ◽  
Reaction Pathways ◽  
Peroxy Radicals ◽  
Flight Mass Spectrometer

Abstract. Gas-phase oxidation pathways and products of anthropogenic volatile organic compounds (VOCs), mainly aromatics, are the subject of intensive research with attention paid to their contributions to secondary organic aerosol (SOA) formation and potentially, new particle formation (NPF) in the urban atmosphere. In this study, a series of OH-initiated oxidation experiments of trimethylbenzene (TMB, C9H12) including 1,2,4-TMB, 1,3,5-TMB, 1,2,3-TMB, and 1,2,4-(methyl-D3)-TMBs (C9H9D3) were investigated in an oxidation flow reactor (OFR), in the absence and presence of NOx. Products were measured using a suite of state-of-the-art instruments, i.e., a nitrate-based chemical ionization – atmospheric pressure interface time-of-flight mass spectrometer (Nitrate CI-APi-TOF), an iodide-adduct chemical ionization – time-of-flight mass spectrometer (Iodide CI-TOF) equipped with a Filter Inlet for Gases and AEROsols (FIGAERO), and a Vocus proton-transfer-reaction mass spectrometer (Vocus PTR). A large number of C9 products with 1–11 oxygen atoms and C18 products presumably formed from dimerization of C9 peroxy radicals were observed, hinting the extensive existence of autoxidation and accretion reaction pathways in the OH-initiated oxidation reactions of TMBs. Oxidation products of 1,2,4-(methyl-D3)-TMBs with deuterium atoms in different methyl substituents were then used as a molecular basis to propose potential autoxidation reaction pathways. Accretion of C9 peroxy radicals is the most significant for aromatics with meta-substituents and the least for aromatics with ortho-substituents, if the number and size of substituted groups are identical. The presence of NOx would suppress the formation of C18 highly oxygenated molecules (HOMs) and enhance the formation of organonitrates, and even dinitrate organic compounds. Our results show that the oxidation products of TMB are much more diverse and could be more oxygenated than the current mechanisms predict.

scholarly journals Evaluating the performance of five different chemical ionization techniques for detecting gaseous oxygenated organic species

2019 ◽  
Vol 12 (4) ◽  
pp. 2403-2421 ◽  
Author(s):  
Matthieu Riva ◽  
Pekka Rantala ◽  
Jordan E. Krechmer ◽  
Otso Peräkylä ◽  
Yanjun Zhang ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Time Of Flight ◽  
Mass Spectrometers ◽  
Organic Species ◽  
Flight Mass Spectrometer ◽  
Wide Range ◽  
Volatile Organic

Abstract. The impact of aerosols on climate and air quality remains poorly understood due to multiple factors. One of the current limitations is the incomplete understanding of the contribution of oxygenated products, generated from the gas-phase oxidation of volatile organic compounds (VOCs), to aerosol formation. Indeed, atmospheric gaseous chemical processes yield thousands of (highly) oxygenated species, spanning a wide range of chemical formulas, functional groups and, consequently, volatilities. While recent mass spectrometric developments have allowed extensive on-line detection of a myriad of oxygenated organic species, playing a central role in atmospheric chemistry, the detailed quantification and characterization of this diverse group of compounds remains extremely challenging. To address this challenge, we evaluated the capability of current state-of-the-art mass spectrometers equipped with different chemical ionization sources to detect the oxidation products formed from α-Pinene ozonolysis under various conditions. Five different mass spectrometers were deployed simultaneously for a chamber study. Two chemical ionization atmospheric pressure interface time-of-flight mass spectrometers (CI-APi-TOF) with nitrate and amine reagent ion chemistries and an iodide chemical ionization time-of-flight mass spectrometer (TOF-CIMS) were used. Additionally, a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF 8000) and a new “vocus” PTR-TOF were also deployed. In the current study, we compared around 1000 different compounds between each of the five instruments, with the aim of determining which oxygenated VOCs (OVOCs) the different methods were sensitive to and identifying regions where two or more instruments were able to detect species with similar molecular formulae. We utilized a large variability in conditions (including different VOCs, ozone, NOx and OH scavenger concentrations) in our newly constructed atmospheric simulation chamber for a comprehensive correlation analysis between all instruments. This analysis, combined with estimated concentrations for identified molecules in each instrument, yielded both expected and surprising results. As anticipated based on earlier studies, the PTR instruments were the only ones able to measure the precursor VOC, the iodide TOF-CIMS efficiently detected many semi-volatile organic compounds (SVOCs) with three to five oxygen atoms, and the nitrate CI-APi-TOF was mainly sensitive to highly oxygenated organic (O > 5) molecules (HOMs). In addition, the vocus showed good agreement with the iodide TOF-CIMS for the SVOC, including a range of organonitrates. The amine CI-APi-TOF agreed well with the nitrate CI-APi-TOF for HOM dimers. However, the loadings in our experiments caused the amine reagent ion to be considerably depleted, causing nonlinear responses for monomers. This study explores and highlights both benefits and limitations of currently available chemical ionization mass spectrometry instrumentation for characterizing the wide variety of OVOCs in the atmosphere. While specifically shown for the case of α-Pinene ozonolysis, we expect our general findings to also be valid for a wide range of other VOC–oxidant systems. As discussed in this study, no single instrument configuration can be deemed better or worse than the others, as the optimal instrument for a particular study ultimately depends on the specific target of the study.

scholarly journals Evaluating the performance of five different chemical ionization techniques for detecting gaseous oxygenated organic species

2018 ◽  
Author(s):  
Matthieu Riva ◽  
Pekka Rantala ◽  
Jordan E. Krechmer ◽  
Otso Peräkylä ◽  
Yanjun Zhang ◽  
...  
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Time Of Flight ◽  
Mass Spectrometers ◽  
Organic Species ◽  
Flight Mass Spectrometer ◽  
Wide Range ◽  
Volatile Organic

Abstract. The impact of aerosols on climate and air quality remains poorly understood due to multiple factors. One of the current limitations is the incomplete understanding of the contribution of oxygenated products, generated from the gas-phase oxidation of volatile organic compounds (VOC), to aerosol formation. Indeed, atmospheric gaseous chemical processes yield thousands of (highly) oxygenated species, spanning a wide range of chemical formulas, functional groups and, consequently, volatilities. While recent mass spectrometric developments have allowed extensive on-line detection of a myriad of oxygenated organic species, playing a central role in atmospheric chemistry, the detailed quantification and characterization of this diverse group of compounds remains extremely challenging. To address this challenge, we evaluated the capability of current state-of-the-art mass spectrometers equipped with different chemical ionization sources to detect the oxidation products formed from α-pinene ozonolysis under various conditions. Five different mass spectrometers were deployed simultaneously for a chamber study. Two chemical ionization atmospheric pressure interface time-of-flight mass spectrometers (CI-APi-TOF) with nitrate and amine reagent ion chemistries and an iodide chemical ionization time-of-flight mass spectrometer (TOF-CIMS). Additionally, a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF 8000) and a new “Vocus” PTR-TOF were also deployed. In the current study, we compared around 1000 different compounds between each of the five instruments, with the aim to determine which oxygenated VOC (OVOC) the different methods were sensitive to, and identifying regions where two or more instruments were able to detect species with similar molecular formulae. We utilized a large variability in conditions (including different VOC, ozone, NOx and OH scavenger concentrations) in our newly constructed atmospheric simulation chamber for a comprehensive correlation analysis between all instruments. This analysis, combined with estimated concentrations for identified molecules in each instrument, yielded both expected and surprising results. As anticipated based on earlier studies: the PTR instruments were the only ones able to measure the precursor VOC; the iodide TOF-CIMS efficiently detected many semi-volatile organic compounds (SVOC) with 3 to 5 oxygen atoms; and the nitrate CI-APi-TOF was mainly sensitive to highly-oxygenated organic (O > 5) molecules (HOM). In addition, the Vocus showed good agreement with the iodide TOF-CIMS for the SVOC, including also a range of organonitrates. The amine CI-APi-TOF agreed well with the nitrate CI-APi-TOF for HOM dimers. However, the loadings in our experiments caused the amine reagent ion to be considerably depleted, causing non-linear responses for monomers. This study explores and highlights both benefits and limitations of currently available chemical ionization mass spectrometry instrumentation for characterizing the wide variety of OVOC in the atmosphere. While specifically shown for the case of α-pinene ozonolysis, we expect our general findings to be valid also for a wide range of other VOC-oxidant systems. As discussed in this study, no single instrument configuration can be deemed better or worse than the others, as the optimal instrument for a particular study ultimately depends on the specific target of the study.

scholarly journals Furthering information from OH and HO<sub>2</sub> +RO<sub>2</sub> observations using a high resolution time of flight mass spectrometer

2016 ◽  
Author(s):  
R. L. Mauldin III ◽  
M. P. Rissanen ◽  
T. Petäjä ◽  
M. Kulmala
Keyword(s):  
High Resolution ◽  
Mass Spectrometer ◽  
Atmospheric Pressure ◽  
Chemical Ionization ◽  
Time Of Flight ◽  
Chemical Conversion ◽  
Oxidation Products ◽  
Organic Species ◽  
Flight Mass Spectrometer ◽  
Volatile Organic

Abstract. An instrument has been developed which allows an entire suite of oxidation products (H2SO4 and Extremely Low Volatile Organic Compounds, ELVOCs) to be measured along with the concentrations of the key radical species OH and HO2 +RO2. The system combines the techniques for chemical conversion of OH or HO2 +RO2 into H2SO4 together with nitrate ion (NO3-) Chemical Ionization (CI) and Atmospheric Pressure interface - Time of Flight Mass Spectrometer (NO3- CI-APi-ToF) which has been previously used for the detection of ELVOCs and a few other oxygenated organic species. The system exhibits the same sensitivity towards OH or HO2 +RO2 as previous quadrupole chemical ionization (CIMS) measurements with limits of detection of ~2 x 105 and ~2 x 106 molecule cm-3 for OH and HO2+RO2 respectively. Unlike previous CIMS measurements, the use of a NO3- CI-APi-ToF allows the acquisition of the entire mass spectrum at high resolution with each measurement, allowing one to see how the organic species behave when the sample flow is perturbed with reagent gasses (SO2 or NO). While the combination of these measurements into one instrument is of great practical value, it is the combination of these data within the spectra obtained in each mode that extends the information far beyond the measurements themselves.

scholarly journals Technical Note: Performance of Chemical Ionization Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS) for the measurement of atmospherically significant oxygenated volatile organic compounds

2007 ◽  
Vol 7 (3) ◽  
pp. 609-620 ◽  
Author(s):  
K. P. Wyche ◽  
R. S. Blake ◽  
A. M. Ellis ◽  
P. S. Monks ◽  
T. Brauers ◽  
...  
Keyword(s):  
Reaction Time ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Time Of Flight ◽  
Mixing Ratios ◽  
Flight Mass Spectrometer ◽  
Accuracy And Precision ◽  
Ionization Reaction ◽  
Volatile Organic ◽  
Tof Ms

Abstract. The performance of a new chemical ionization reaction time-of-flight mass spectrometer (CIR-TOF-MS) utilising the environment chamber SAPHIR (Simulation of Atmospheric Photochemistry In a large Reaction Chamber- Forschungzentrum Jülich, Germany) is described. The work took place as part of the ACCENT (Atmospheric Composition and Change the European NeTwork for excellence) supported oxygenated volatile organic compound (OVOC) measurement intercomparison during January 2005. The experiment entailed the measurement of 14 different atmospherically significant OVOCs at various mixing ratios in the approximate range 10.0–0.6 ppbV. The CIR-TOF-MS operated throughout the exercise with the hydronium ion (H3O+) as the primary chemical ionization (CI) reagent in order to facilitate proton transfer to the analyte OVOCs. The results presented show that the CIR time-of-flight mass spectrometer is capable of detecting a wide range of atmospheric OVOCs at mixing ratios of around 10 ppbV in "real-time" (i.e. detection on the one-minute time scale), with sub-ppbV measurement also achieved following an increase in averaging time to tens of minutes. It is shown that in general OVOC measurement is made with high accuracy and precision, with integration time, mixing ratio and compound dependent values as good as 4–13% and 3–15% respectively. It is demonstrated that CIR-TOF-MS has rapid multi-channel response at the required sensitivity, accuracy and precision for atmospheric OVOC measurement.

Eddy covariance (EC) fluxes of monoterpene oxidation products from a boreal forest canopy

2020 ◽  
Author(s):  
Lejish Vettikkat ◽  
Arttu Ylisirniö ◽  
Iida Pullinen ◽  
Luís Miguel Feijó Barreira ◽  
Pasi Miettinen ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Eddy Covariance ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Time Of Flight ◽  
Ground Level ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Aerosol Formation ◽  
Flux Measurements

&lt;p&gt;Oxidation of volatile organic compounds (VOC) by ozone (O&lt;sub&gt;3&lt;/sub&gt;), hydroxyl radicals (OH) and nitrogen oxide radicals (NO&lt;sub&gt;3&lt;/sub&gt;, NOx) reduces their volatility and leads to the formation of secondary organic aerosols (SOA) through gas-particle partitioning. Recent studies have shown that monoterpene (C&lt;sub&gt;10&lt;/sub&gt;H&lt;sub&gt;16&lt;/sub&gt;) oxidation products can participate in all stages of aerosol formation, especially in forested boreal environments. However, deposition of these semi-volatile and (extremely) low-volatility organic compounds (SVOC, LVOC, ELVOC) to surfaces in the canopy directly competes with the gas-particle partitioning and has a substantial effect (~50%) on organic aerosol loading. Hence understanding the fate of these oxidation products is crucial in determining the organic aerosol budget and thereby constraining their contribution to climate-relevant processes such as new-particle formation and cloud formation.&lt;/p&gt;&lt;p&gt;Oxidation products of monoterpenes were measured at the station for measuring ecosystem atmosphere relations (SMEAR II), a boreal forest research station in Hyyti&amp;#228;l&amp;#228;, Finland, in spring/summer 2019. The forest is dominated by Scots pine (&lt;em&gt;Pinus sylvestris&lt;/em&gt; L.) and Norway spruce (&lt;em&gt;Picea abies&lt;/em&gt; (L.) H. Karst) which are well known high monoterpene emitters. Eddy covariance (EC) flux measurements of oxygenated organic compounds in the gas phase were performed using an iodide-adduct high-resolution time-of-flight chemical ionization mass spectrometer (I-CIMS) with high frequency (5 Hz) co-located with a sonic anemometer (METEK USA-1) on a tower, 35 m above the forest floor. The ion-molecule reaction (IMR) chamber of I-CIMS was actively humidified to mitigate the dependence of the sensitivity of the measurements on the ambient relative humidity. The EC data were analysed following standard correction procedures like lag correction, coordinate rotation and uncertainty analysis. VOCs and oxygenated VOCs were also measured at ground level using a Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus PTR-MS), which is sensitive also to the majority of compounds measured by I-CIMS.&lt;/p&gt;&lt;p&gt;We present the first continuous I-CIMS dataset at high time resolution (5 Hz) from a tall tower and calculate the Eddy covariance fluxes of a wide range of monoterpene oxidation products during the primary plant-growth season in a boreal forest. Bidirectional fluxes for formic acid (HCOOH) were observed at a higher temporal resolution than reported in earlier studies. We found an increasing trend in the deposition velocity for heavier monoterpene oxidation products which enables us to constrain the net flow of organics between the atmosphere and the canopy layer using the continuity/mass balance equation. When coupled to ground-based measurements using Vocus-PTR, our EC flux measurements will give further insight about the abundance of organics above the canopy vs near ground-level. We also plan to integrate our observations with a chemical transport model containing details of monoterpene oxidation chemistry (ADCHEM) to simulate the sources and sinks and to derive parameterizations for representing the dry deposition rates of monoterpene oxidation products in the boreal forested environments.&lt;/p&gt;

scholarly journals Coupling a gas chromatograph simultaneously to a flame ionization detector and chemical ionization mass spectrometer for isomer-resolved measurements of particle-phase organic compounds

2020 ◽  
Author(s):  
Chenyang Bi ◽  
Jordan E. Krechmer ◽  
Graham O. Frazier ◽  
Wen Xu ◽  
Andrew T. Lambe ◽  
...  
Keyword(s):  
Functional Groups ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Measurement Techniques ◽  
Oxidation Products ◽  
Ionization Mass ◽  
Particle Phase ◽  
Gas Chromatograph ◽  
New Instrument

Abstract. Atmospheric oxidation products of volatile organic compounds consist of thousands of unique chemicals that have distinctly different physical and chemical properties depending on their detailed structures and functional groups. Measurement techniques that can achieve molecular characterizations with details down to functional groups (i.e., isomer-resolved resolution) are consequently necessary to provide understandings of differences of fate and transport within isomers produced in the oxidation process. We demonstrate a new instrument coupling the thermal desorption aerosol gas chromatograph (TAG), which enables the separation of isomers, with the high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS), which has the capability of classifying unknown compounds by their molecular formulas, and the flame ion detector (FID), which provide a near-universal response to organic compounds. The TAG-CIMS/FID is used to provide isomer-resolved measurements of samples from liquid standard injections and particle-phase organics generated in oxidation flow reactors. By coupling a TAG to a CIMS, the CIMS is enhanced with an additional dimension of information (resolution of individual molecules) at the cost of time resolution (i.e., one sample per hour instead of per minute). We found that isomers are prevalent in sample matrix with an average number of three to five isomers per formula depending on the precursors in the oxidation experiments. Additionally, a multi-reagent ionization mode is investigated in which both zero air and iodide are introduced as reagent ions, to examine the feasibility of extending the use of an individual CIMS to a broader range of analytes with still selective reagent ions. While this approach reduces iodide-adduct ions by a factor of two, [M−H]− and [M+O2]− ions produced from lower-polarity compounds increase by a factor of five to ten, improving their detection by CIMS. The method expands the range of detected chemical species by using two chemical ionization reagents simultaneously, enabled by the pre-separation of analyte molecules before ionization.

An Iodide-Adduct High-Resolution Time-of-Flight Chemical-Ionization Mass Spectrometer: Application to Atmospheric Inorganic and Organic Compounds

2014 ◽  
Vol 48 (11) ◽  
pp. 6309-6317 ◽  
Author(s):  
Ben H. Lee ◽  
Felipe D. Lopez-Hilfiker ◽  
Claudia Mohr ◽  
Theo Kurtén ◽  
Douglas R. Worsnop ◽  
...  
Keyword(s):  
High Resolution ◽  
Organic Compounds ◽  
Mass Spectrometer ◽  
Chemical Ionization ◽  
Time Of Flight ◽  
Ionization Mass ◽  
Resolution Time ◽  
Inorganic And Organic
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