scholarly journals Molecular composition and volatility of isoprene photochemical oxidation secondary organic aerosol under low and high NO<sub>x</sub> conditions

2016 ◽  
Author(s):  
Emma L. D'Ambro ◽  
Ben H. Lee ◽  
Jiumeng Liu ◽  
John E. Shilling ◽  
Cassandra J. Gaston ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Group Contribution ◽  
Molecular Composition ◽  
Photochemical Oxidation ◽  
Organic Nitrates ◽  
Ionization Mass ◽  
Equilibrium Partitioning ◽  
Group Contribution Methods

Abstract. We present measurements of secondary organic aerosol (SOA) formation from isoprene photochemical oxidation formed in an environmental simulation chamber using dry neutral seed particles, thereby suppressing the role of acid catalyzed multiphase chemistry, at a variety of oxidant conditions. A high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS) utilizing iodide-adduct ionization coupled to the Filter Inlet for Gases and AEROsols (FIGAERO) allowed for the simultaneous online sampling of the gas and particle composition. Under high HO2 and low NO conditions, highly oxygenated (O : C ≥ 1) C5 compounds were major components (~ 50 %) of the SOA. The overall composition of the SOA evolved both as a function of time and as a function of input NO concentrations. As the level of input NO increased, organic nitrates increased in both the gas- and particle-phases, but the dominant non-nitrate particle-phase components monotonically decreased. We use comparisons of measured and predicted gas-particle partitioning of individual components to assess the validity of literature-based group-contribution methods for estimating saturation vapor concentrations. While there is evidence for equilibrium partitioning being achieved on the chamber residence time scale (5.2 hours) for some individual components, significant errors in group-contribution methods are revealed. In addition, > 30 % of the SOA mass, detected as low-molecular weight compounds, cannot be reconciled with equilibrium partitioning. These compounds desorb from the FIGAERO at unexpectedly high temperatures given their molecular composition, indicative of thermal decomposition of effectively lower volatility components, likely larger molecular weight oligomers. We use these insights from the laboratory and observations of the same SOA components made during the Southern Oxidant and Aerosol Study (SOAS) to assess the importance of isoprene photooxidation as a local SOA source.

scholarly journals Molecular composition and volatility of isoprene photochemical oxidation secondary organic aerosol under low- and high-NO<sub><i>x</i></sub> conditions

2017 ◽  
Vol 17 (1) ◽  
pp. 159-174 ◽  
Author(s):  
Emma L. D'Ambro ◽  
Ben H. Lee ◽  
Jiumeng Liu ◽  
John E. Shilling ◽  
Cassandra J. Gaston ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Group Contribution ◽  
Molecular Composition ◽  
Photochemical Oxidation ◽  
Organic Nitrates ◽  
Ionization Mass ◽  
Equilibrium Partitioning ◽  
Group Contribution Methods

Abstract. We present measurements of secondary organic aerosol (SOA) formation from isoprene photochemical oxidation in an environmental simulation chamber at a variety of oxidant conditions and using dry neutral seed particles to suppress acid-catalyzed multiphase chemistry. A high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) utilizing iodide-adduct ionization coupled to the Filter Inlet for Gases and Aerosols (FIGAERO) allowed for simultaneous online sampling of the gas and particle composition. Under high-HO2 and low-NO conditions, highly oxygenated (O : C  ≥  1) C5 compounds were major components (∼ 50 %) of SOA. The SOA composition and effective volatility evolved both as a function of time and as a function of input NO concentrations. Organic nitrates increased in both the gas and particle phases as input NO increased, but the dominant non-nitrate particle-phase components monotonically decreased. We use comparisons of measured and predicted gas-particle partitioning of individual components to assess the validity of literature-based group-contribution methods for estimating saturation vapor concentrations. While there is evidence for equilibrium partitioning being achieved on the chamber residence timescale (5.2 h) for some individual components, significant errors in group-contribution methods are revealed. In addition, > 30 % of the SOA mass, detected as low-molecular-weight semivolatile compounds, cannot be reconciled with equilibrium partitioning. These compounds desorb from the FIGAERO at unexpectedly high temperatures given their molecular composition, which is indicative of thermal decomposition of effectively lower-volatility components such as larger molecular weight oligomers.

Evidence for a kinetically controlled burying mechanism for growth of high viscosity secondary organic aerosol

2020 ◽  
Vol 22 (1) ◽  
pp. 66-83 ◽  
Author(s):  
Allison C. Vander Wall ◽  
Véronique Perraud ◽  
Lisa M. Wingen ◽  
Barbara J. Finlayson-Pitts
Keyword(s):  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
High Viscosity ◽  
Particle Formation ◽  
Organic Nitrates ◽  
Equilibrium Partitioning ◽  
Kinetically Controlled

The incorporation of organic nitrates into viscous secondary organic aerosol during particle formation is enhanced relative to expected equilibrium partitioning, and is best described by a kinetically controlled “burying” mechanism.

scholarly journals High-molecular-weight esters in α-pinene ozonolysis secondary organic aerosol: Structural characterization and mechanistic proposal for their formation from highly oxygenated molecules

2018 ◽  
Author(s):  
Ariane Kahnt ◽  
Reinhilde Vermeylen ◽  
Yoshiteru Iinuma ◽  
Mohammad Safi Shalamzari ◽  
Willy Maenhaut ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Molecular Weight ◽  
Gas Phase ◽  
High Molecular Weight ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Molecular Structures ◽  
Ionization Mass ◽  
Alkoxy Radical ◽  
Pinic Acid

Abstract. Stable high-molecular-weight esters are present in α-pinene ozonolysis secondary organic aerosol (SOA) with the two most abundant ones corresponding to a diaterpenylic ester of cis-pinic acid with a molecular weight (MW) of 368 C19H28O7) and a hydroxypinonyl ester of cis-pinic acid with a MW of 358 (C17H26O8). However, their molecular structures are not completely elucidated and their relationship with highly oxygenated molecules (HOMs) in the gas phase is still unclear. In this study, liquid chromatography in combination with positive ion electrospray ionization mass spectrometry has been performed on high-molecular-weight esters present in α-pinene/O3 SOA with and without derivatization into methyl esters. Unambiguous evidence could be obtained for the molecular structure of the MW 368 ester in that it corresponds to an ester of cis-pinic acid where the carboxyl substituent of the dimethylcyclobutane ring and not the methylcarboxyl substituent is esterified with 7-hydroxypinonic acid. The same linkage was already proposed in previous work for the MW 358 ester (Yasmeen et al., 2010), but could be supported in the present study. Guided by the molecular structures of these stable esters, we propose a formation mechanism from gas-phase HOMs that takes into account the formation of an unstable C19H28O11 product, which is detected as a major species in α-pinene ozonolysis experiments as well as in the pristine forest atmosphere by chemical ionization – atmospheric pressure ionization – time-of-flight mass spectrometry with nitrate clustering (Ehn et al., 2012, 2014). It is suggested that an acyl peroxy radical related to cis-pinic acid (RO2·) and an alkoxy radical related to 7- or 5-hydroxypinonic acid (R'O·) serve as key gas-phase radicals and combine according to a RO2· + R'O· → RO3R' radical termination reaction. Subsequently, the unstable C19H28O11

scholarly journals High-molecular-weight esters in <i>α</i>-pinene ozonolysis secondary organic aerosol: structural characterization and mechanistic proposal for their formation from highly oxygenated molecules

2018 ◽  
Vol 18 (11) ◽  
pp. 8453-8467 ◽  
Author(s):  
Ariane Kahnt ◽  
Reinhilde Vermeylen ◽  
Yoshiteru Iinuma ◽  
Mohammad Safi Shalamzari ◽  
Willy Maenhaut ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Molecular Weight ◽  
Gas Phase ◽  
High Molecular Weight ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Molecular Structures ◽  
Ionization Mass ◽  
Ester Formation ◽  
Pinic Acid

Abstract. Stable high-molecular-weight esters are present in α-pinene ozonolysis secondary organic aerosol (SOA) with the two most abundant ones corresponding to a hydroxypinonyl ester of cis-pinic acid with a molecular weight (MW) of 368 (C19H28O7) and a diaterpenylic ester of cis-pinic acid with a MW of 358 (C17H26O8). However, their molecular structures are not completely elucidated and their relationship with highly oxygenated molecules (HOMs) in the gas phase is still unclear. In this study, liquid chromatography in combination with positive ion electrospray ionization mass spectrometry has been performed on high-molecular-weight esters present in α-pinene ozonolysis SOA with and without derivatization into methyl esters. Unambiguous evidence could be obtained for the molecular structure of the MW 368 ester in that it corresponds to an ester of cis-pinic acid where the carboxyl substituent of the dimethylcyclobutane ring and not the methylcarboxyl substituent is esterified with 7-hydroxypinonic acid. The same linkage was already proposed in previous work for the MW 358 ester (Yasmeen et al., 2010), but could be supported in the present study. Guided by the molecular structures of these stable esters, we propose a formation mechanism from gas-phase HOMs that takes into account the formation of an unstable C19H28O11 product, which is detected as a major species in α-pinene ozonolysis experiments as well as in the pristine forest atmosphere by chemical ionization–atmospheric pressure ionization–time-of-flight mass spectrometry with nitrate clustering (Ehn et al., 2012, 2014). It is suggested that an acyl peroxy radical related to cis-pinic acid (RO2⚫) and an alkoxy radical related to 7- or 5-hydroxypinonic acid (R′O⚫) serve as key gas-phase radicals and combine according to a RO2 + R′O⚫ → RO3R′ radical termination reaction. Subsequently, the unstable C19H28O11 HOM species decompose through the loss of oxygen or ketene from the inner part containing a labile trioxide function and the conversion of the unstable acyl hydroperoxide groups to carboxyl groups, resulting in stable esters with a molecular composition of C19H28O7 (MW 368) and C17H26O8 (MW 358), respectively. The proposed mechanism is supported by several observations reported in the literature. On the basis of the indirect evidence presented in this study, we hypothesize that RO2 + R′O⚫ → RO3R′ chemistry is at the underlying molecular basis of high-molecular-weight ester formation upon α-pinene ozonolysis and may thus be of importance for new particle formation and growth in pristine forested environments.

scholarly journals Phase, composition, and growth mechanism for secondary organic aerosol from the ozonolysis of <i>α</i>-cedrene

2016 ◽  
Vol 16 (5) ◽  
pp. 3245-3264 ◽  
Author(s):  
Yue Zhao ◽  
Lisa M. Wingen ◽  
Véronique Perraud ◽  
Barbara J. Finlayson-Pitts
Keyword(s):  
Mass Spectrometry ◽  
Molecular Weight ◽  
Flow Reactor ◽  
Secondary Organic Aerosol ◽  
Aldol Condensation ◽  
Reaction Times ◽  
Organic Aerosol ◽  
Particle Formation ◽  
Ionization Mass ◽  
Early Stages

Abstract. Sesquiterpenes are an important class of biogenic volatile organic compounds (BVOCs) and have a high secondary organic aerosol (SOA) forming potential. However, SOA formation from sesquiterpene oxidation has received less attention compared to other BVOCs such as monoterpenes, and the underlying mechanisms remain poorly understood. In this work, we present a comprehensive experimental investigation of the ozonolysis of α-cedrene both in a glass flow reactor (27–44 s reaction times) and in static Teflon chambers (30–60 min reaction times). The SOA was collected by impaction or filters, followed by analysis using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and electrospray ionization mass spectrometry (ESI-MS), or measured online using direct analysis in real-time mass spectrometry (DART-MS) and aerosol mass spectrometry (AMS). The slow evaporation of 2-ethylhexyl nitrate that was incorporated into the SOA during its formation and growth gives an estimated diffusion coefficient of 3  ×  10−15 cm2 s−1 and shows that SOA is a highly viscous semisolid. Possible structures of four newly observed low molecular weight (MW  ≤  300 Da) reaction products with higher oxygen content than those previously reported were identified. High molecular weight (HMW) products formed in the early stages of the oxidation have structures consistent with aldol condensation products, peroxyhemiacetals, and esters. The size-dependent distributions of HMW products in the SOA, as well as the effects of stabilized Criegee intermediate (SCI) scavengers on HMW products and particle formation, confirm that HMW products and reactions of SCI play a crucial role in early stages of particle formation. Our studies provide new insights into mechanisms of SOA formation and growth in α-cedrene ozonolysis and the important role of sesquiterpenes in new particle formation as suggested by field measurements.

scholarly journals Nocturnal isoprene oxidation over the Northeast United States in summer and its impact on reactive nitrogen partitioning and secondary organic aerosol

2009 ◽  
Vol 9 (1) ◽  
pp. 225-269
Author(s):  
S. S. Brown ◽  
J. A. deGouw ◽  
C. Warneke ◽  
T. B. Ryerson ◽  
W. P. Dubé ◽  
...  
Keyword(s):  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Nitrogen Partitioning ◽  
Photochemical Oxidation ◽  
Reactive Nitrogen ◽  
Organic Nitrates ◽  
Isoprene Oxidation ◽  
Northeast Us ◽  
Aircraft Study

Abstract. Isoprene is the largest single VOC emission to the atmosphere. Although it is primarily oxidized photochemically during daylight hours, late-day emissions that remain in the atmosphere at sunset undergo oxidation by NO3 in regionally polluted areas with large NOx levels. A recent aircraft study examined isoprene and its nocturnal oxidants in a series of night flights across the Northeast US, a region with large emissions of both isoprene and NOx. Substantial amounts of isoprene that were observed after dark were strongly anticorrelated with measured NO3 and were the most important factor determining the lifetime of this radical. The products of photochemical oxidation of isoprene, methyl vinyl ketone and methacrolein, were more uniformly distributed, and served as tracers for the presence of isoprene at sunset, prior to its oxidation by NO3. Comparison of a determination of the mass of isoprene oxidized in darkness by NO3 to a calculation of integrated isoprene emissions showed that large amounts (>20%) of emitted isoprene may undergo nocturnal oxidation in this region. Organic nitrates produced from the NO3+isoprene reaction, though not directly measured, were estimated to account for 2–9% of total reactive nitrogen and 7–31% of other long-lived organic nitrates such as PAN. The mass of isoprene oxidized by NO3 was comparable to and correlated with the organic aerosol loading for flights with relatively low organic aerosol background. The contribution of nocturnal isoprene oxidation to secondary organic aerosol was determined in the range 1–17%, and isoprene SOA mass derived from NO3 was calculated to exceed that due to OH by approximately 50%.

scholarly journals Nocturnal isoprene oxidation over the Northeast United States in summer and its impact on reactive nitrogen partitioning and secondary organic aerosol

2009 ◽  
Vol 9 (9) ◽  
pp. 3027-3042 ◽  
Author(s):  
S. S. Brown ◽  
J. A. deGouw ◽  
C. Warneke ◽  
T. B. Ryerson ◽  
W. P. Dubé ◽  
...  
Keyword(s):  
Secondary Organic Aerosol ◽  
Large Fraction ◽  
Organic Aerosol ◽  
Nitrogen Partitioning ◽  
Photochemical Oxidation ◽  
Reactive Nitrogen ◽  
Organic Nitrates ◽  
Isoprene Oxidation ◽  
Northeast Us

Abstract. Isoprene is the largest single VOC emission to the atmosphere. Although it is primarily oxidized photochemically during daylight hours, late-day emissions that remain in the atmosphere at sunset undergo oxidation by NO3 in regionally polluted areas with large NOx levels. A recent aircraft study examined isoprene and its nocturnal oxidants in a series of night flights across the Northeast US, a region with large emissions of both isoprene and NOx. Substantial amounts of isoprene that were observed after dark were strongly anticorrelated with measured NO3 and were the most important factor determining the lifetime of this radical. The products of photochemical oxidation of isoprene, methyl vinyl ketone and methacrolein, were more uniformly distributed, and served as tracers for the presence of isoprene at sunset, prior to its oxidation by NO3. A determination of the mass of isoprene oxidized in darkness showed it to be a large fraction (>20%) of emitted isoprene. Organic nitrates produced from the NO3+isoprene reaction, though not directly measured, were estimated to account for 2–9% of total reactive nitrogen. The mass of isoprene oxidized by NO3 was comparable to and correlated with the organic aerosol loading for flights with relatively low organic aerosol background. The contribution of nocturnal isoprene oxidation to secondary organic aerosol was determined in the range 1–17%, and isoprene SOA mass derived from NO3 was calculated to exceed that due to OH by approximately 50%.

scholarly journals Characterization of organic nitrate constituents of secondary organic aerosol (SOA) from nitrate-radical-initiated oxidation of limonene using high-resolution chemical ionization mass spectrometry

2018 ◽  
Vol 18 (8) ◽  
pp. 5467-5481 ◽  
Author(s):  
Cameron Faxon ◽  
Julia Hammes ◽  
Michael Le Breton ◽  
Ravi Kant Pathak ◽  
Mattias Hallquist
Keyword(s):  
High Resolution ◽  
Chemical Ionization ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Formation Mechanisms ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Ionization Mass ◽  
Nitrate Radical ◽  
Particle Phase

Abstract. The gas-phase nitrate radical (NO3⚫) initiated oxidation of limonene can produce organic nitrate species with varying physical properties. Low-volatility products can contribute to secondary organic aerosol (SOA) formation and organic nitrates may serve as a NOx reservoir, which could be especially important in regions with high biogenic emissions. This work presents the measurement results from flow reactor studies on the reaction of NO3⚫ with limonene using a High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS) combined with a Filter Inlet for Gases and AEROsols (FIGAERO). Major condensed-phase species were compared to those in the Master Chemical Mechanism (MCM) limonene mechanism, and many non-listed species were identified. The volatility properties of the most prevalent organic nitrates in the produced SOA were determined. Analysis of multiple experiments resulted in the identification of several dominant species (including C10H15NO6, C10H17NO6, C8H11NO6, C10H17NO7, and C9H13NO7) that occurred in the SOA under all conditions considered. Additionally, the formation of dimers was consistently observed and these species resided almost completely in the particle phase. The identities of these species are discussed, and formation mechanisms are proposed. Cluster analysis of the desorption temperatures corresponding to the analyzed particle-phase species yielded at least five distinct groupings based on a combination of molecular weight and desorption profile. Overall, the results indicate that the oxidation of limonene by NO3⚫ produces a complex mixture of highly oxygenated monomer and dimer products that contribute to SOA formation.

scholarly journals Characterization of organic nitrate constituents of secondary organic aerosol (SOA) from nitrate-radical-initiated oxidation of limonene using High-Resolution Chemical Ionization Mass Spectrometry

2017 ◽  
Author(s):  
Cameron Faxon ◽  
Julia Hammes ◽  
Ravi Kant Pathak ◽  
Mattias Hallquist
Keyword(s):  
High Resolution ◽  
Chemical Ionization ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Formation Mechanisms ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Ionization Mass ◽  
Nitrate Radical ◽  
Particle Phase

Abstract. The gas phase nitrate radical (NO3•) initiated oxidation of limonene can produce organic nitrate species with varying physical properties. Low-volatility products can contribute to secondary organic aerosol (SOA) formation and organic nitrates may serve as a NOx reservoir, which could be especially important in regions with high biogenic emissions. This work presents the measurement results from flow reactor studies on the reaction of NO3• and limonene using a High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-ToF-CIMS) combined with a Filter Inlet for Gases and AEROsols (FIGAERO). Major condensed-phase species were identified, and the identity and volatility properties of the most prevalent organic nitrates in the produced SOA were determined. Analysis of multiple experiments resulted in the identification of several dominant species (including C10H15NO6, C10H17NO6, C8H11NO6, C10H17NO7, and C9H13NO7) that occurred in the SOA under all conditions considered. The observed and expected (listed) products (associated with the Master Chemical Mechanism (MCM) limonene mechanism) were compared, and many non-listed species were identified. Additionally, the formation of dimers was consistently observed and these species resided almost completely in the particle phase. The identities of these species are discussed, and formation mechanisms are proposed. Cluster analysis of the desorption temperatures corresponding to the analyzed particle-phase species yielded at least five distinct groupings based on a combination of molecular weight and desorption profile. Overall, the results indicate that the oxidation of limonene by NO3• produces a complex mixture of highly oxygenated monomer and dimer products that contribute to SOA formation.

scholarly journals Phase, composition and growth mechanism for secondary organic aerosol from the ozonolysis of α-cedrene

2015 ◽  
Vol 15 (23) ◽  
pp. 34981-35034 ◽  
Author(s):  
Y. Zhao ◽  
L. M. Wingen ◽  
V. Perraud ◽  
B. J. Finlayson-Pitts
Keyword(s):  
Mass Spectrometry ◽  
Molecular Weight ◽  
Flow Reactor ◽  
Secondary Organic Aerosol ◽  
Aldol Condensation ◽  
Reaction Times ◽  
Organic Aerosol ◽  
Particle Formation ◽  
Ionization Mass ◽  
Early Stages

Abstract. Sesquiterpenes are an important class of biogenic volatile organic compounds (BVOCs) and have a high secondary organic aerosol (SOA) forming potential. However, SOA formation from sesquiterpene oxidation has received less attention compared to other BVOCs such as monoterpenes, and the underlying mechanisms remain poorly understood. In this work, we present a comprehensive experimental investigation of the ozonolysis of α-cedrene both in a glass flow reactor (27–44 s reaction times) and in static Teflon chambers (30–60 min reaction times). The SOA was collected by impaction or filters, followed by analysis using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and electrospray ionization mass spectrometry (ESI-MS), or measured on line using direct analysis in real time (DART-MS) and aerosol mass spectrometry (AMS). The slow evaporation of 2-ethylhexyl nitrate that was incorporated into the SOA during its formation and growth gives an estimated diffusion coefficient of 3 × 10−15 cm2 s−1 and shows that SOA is a highly viscous semi-solid. Possible structures of four newly observed low molecular weight (MW ≤ 300 Da) reaction products with higher oxygen content than those previously reported were identified. High molecular weight (HMW) products formed in the early stages of the oxidation have structures consistent with aldol condensation products, peroxyhemiacetals, and esters. The size-dependent distributions of HMW products in the SOA, as well as the effects of stabilized Criegee intermediate (SCI) scavengers on HMW products and particle formation, confirm that HMW products and reactions of Criegee intermediates play a crucial role in early stages of particle formation. Our studies provide new insights into mechanisms of SOA formation and growth in α-cedrene ozonolysis and the important role of sesquiterpenes in new particle formation as suggested by field measurements.

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