scholarly journals α-pinene photooxidation under controlled chemical conditions – Part 1: Gas-phase composition in low- and high-NO<sub>x</sub> environments

2012 ◽  
Vol 12 (14) ◽  
pp. 6489-6504 ◽  
Author(s):  
N. C. Eddingsaas ◽  
C. L. Loza ◽  
L. D. Yee ◽  
J. H. Seinfeld ◽  
P. O. Wennberg
Keyword(s):  
Gas Phase ◽  
Carboxylic Acids ◽  
First Generation ◽  
Peroxy Radical ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Peroxy Radicals ◽  
Alkoxy Radical ◽  
Alkyl Peroxy Radicals ◽  
Chemical Conditions

Abstract. The OH oxidation of α-pinene under both low- and high-NOx environments was studied in the Caltech atmospheric chambers. Ozone was kept low to ensure OH was the oxidant. The initial α-pinene concentration was 20–50 ppb to ensure that the dominant peroxy radical pathway under low-NOx conditions is reaction with HO2, produced from reaction of OH with H2O2, and under high-NOx conditions, reactions with NO. Here we present the gas-phase results observed. Under low-NOx conditions the main first generation oxidation products are a number of α-pinene hydroxy hydroperoxides and pinonaldehyde, accounting for over 40% of the yield. In all, 65–75% of the carbon can be accounted for in the gas phase; this excludes first-generation products that enter the particle phase. We suggest that pinonaldehyde forms from RO2 + HO2 through an alkoxy radical channel that regenerates OH, a mechanism typically associated with acyl peroxy radicals, not alkyl peroxy radicals. The OH oxidation and photolysis of α-pinene hydroxy hydroperoxides leads to further production of pinonaldehyde, resulting in total pinonaldehyde yield from low-NOx OH oxidation of ~33%. The low-NOx OH oxidation of pinonaldehyde produces a number of carboxylic acids and peroxyacids known to be important secondary organic aerosol components. Under high-NOx conditions, pinonaldehyde was also found to be the major first-generation OH oxidation product. The high-NOx OH oxidation of pinonaldehyde did not produce carboxylic acids and peroxyacids. A number of organonitrates and peroxyacyl nitrates are observed and identified from α-pinene and pinonaldehyde.

scholarly journals α-pinene photooxidation under controlled chemical conditions – Part 1: Gas-phase composition in low- and high-NO<sub>x</sub> environments

2012 ◽  
Vol 12 (3) ◽  
pp. 6447-6483 ◽  
Author(s):  
N. C. Eddingsaas ◽  
C. L. Loza ◽  
L. D. Yee ◽  
J. H. Seinfeld ◽  
P. O. Wennberg
Keyword(s):  
Gas Phase ◽  
Carboxylic Acids ◽  
First Generation ◽  
Peroxy Radical ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Peroxy Radicals ◽  
Alkoxy Radical ◽  
Alkyl Peroxy Radicals ◽  
Chemical Conditions

Abstract. The OH oxidation of α-pinene under both low- and high-NOx environments was studied in the Caltech atmospheric chambers. Ozone was kept low to ensure OH was the oxidant. The initial α-pinene concentration was 20–50 ppb to ensure that the dominant peroxy radical pathway under low-NOx conditions is reaction with HO2 and under high-NOx conditions, reactions with NO. Here we present the gas-phase results observed. Under low-NOx conditions the main first generation oxidation products are α-pinene hydroxy hydroperoxide and pinonaldehyde, accounting for over 40% of the yield. In all, 65–75% of the carbon can be accounted for in the gas phase; this excludes first-generation products that enter the particle phase. We suggest that pinonaldehyde forms from RO2 + HO2 through an alkoxy radical channel that regenerates OH, a mechanism typically associated with acyl peroxy radicals, not alkyl peroxy radicals. The OH oxidation and photolysis of α-pinene hydroxy hydroperoxides leads to further production of pinonaldehyde, resulting in total pinonaldehyde yield from low-NOx OH oxidation of ~33%. The low-NOx OH oxidation of pinonaldehyde produces a number of carboxylic acids and peroxyacids known to be important secondary organic aerosol components. Under high-NOx conditions, pinonaldehyde was also found to be the major first-generation OH oxidation product. The high-NOx OH oxidation of pinonaldehyde did not produce carboxylic acids and peroxyacids. A number of organonitrates and peroxyacyl nitrates are observed and identified from α-pinene and pinonaldehyde.

scholarly journals α-pinene photooxidation under controlled chemical conditions – Part 2: SOA yield and composition in low- and high-NOx environments

2012 ◽  
Vol 12 (4) ◽  
pp. 8579-8615
Author(s):  
N. C. Eddingsaas ◽  
C. L. Loza ◽  
L. D. Yee ◽  
M. Chan ◽  
K. A. Schilling ◽  
...  
Keyword(s):  
Gas Phase ◽  
Ammonium Sulfate ◽  
Carboxylic Acids ◽  
Peroxy Radical ◽  
Organic Aerosol ◽  
Seed Particles ◽  
Field Samples ◽  
Phase Oxidation ◽  
Gas Phase Oxidation ◽  
Chemical Conditions

Abstract. The gas-phase oxidation of α-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with α-pinene have been found in field samples and some are used as tracers of α-pinene oxidation. α-pinene reacts readily with OH and O3 in the atmosphere followed by reactions with both HO2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from low- and high-NOx OH oxidation of α-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O3 concentrations to ensure that OH was the main oxidant and low α-pinene concentrations such that the peroxy radical (RO2) reacted primarily with either HO2 under low-NOx conditions or NO under high-NOx conditions. SOA yield was suppressed under conditions of high-NO. SOA yield under high-NO conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NOx conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NOx products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of α-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under low-NOx conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols.

scholarly journals α-pinene photooxidation under controlled chemical conditions – Part 2: SOA yield and composition in low- and high-NO<sub>x</sub> environments

2012 ◽  
Vol 12 (16) ◽  
pp. 7413-7427 ◽  
Author(s):  
N. C. Eddingsaas ◽  
C. L. Loza ◽  
L. D. Yee ◽  
M. Chan ◽  
K. A. Schilling ◽  
...  
Keyword(s):  
Gas Phase ◽  
Ammonium Sulfate ◽  
Carboxylic Acids ◽  
Peroxy Radical ◽  
Organic Aerosol ◽  
Seed Particles ◽  
Field Samples ◽  
Phase Oxidation ◽  
Gas Phase Oxidation ◽  
Chemical Conditions

Abstract. The gas-phase oxidation of α-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with α-pinene have been found in field samples and some are used as tracers of α-pinene oxidation. α-pinene reacts readily with OH and O3 in the atmosphere followed by reactions with both HO2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from low- and high-NOx OH oxidation of α-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O3 concentrations to ensure that OH was the main oxidant and low α-pinene concentrations such that the peroxy radical (RO2) reacted primarily with either HO2 under low-NOx conditions or NO under high-NOx conditions. SOA yield was suppressed under conditions of high-NOx. SOA yield under high-NOx conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NOx conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NOx products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of α-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under low-NOx conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols.

scholarly journals Formation of Highly Oxygenated Low-Volatility Products from Cresol Oxidation

2016 ◽  
Author(s):  
Rebecca H. Schwantes ◽  
Katherine A. Schilling ◽  
Renee C. McVay ◽  
Hanna Lignell ◽  
Matthew M. Coggon ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Ring Opening ◽  
Chemical Ionization ◽  
First Generation ◽  
Direct Analysis ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Ionization Mass ◽  
Particle Phase

Abstract. Hydroxyl radical (OH) oxidation of toluene produces the ring-retaining products cresol and benzaldehyde, and the ring-opening products bicyclic intermediate compounds and epoxides. Here, first- and later-generation OH oxidation products from cresol and benzaldehyde are identified in laboratory chamber experiments. For benzaldehyde, first-generation ring-retaining products are identified, but later-generation products are not detected. For cresol, low-volatility (saturation mass concentration, C* ~ 3.5 × 104–7.7 × 10−3 μg m−3) first- and later-generation ring-retaining products are identified. Subsequent OH addition to the aromatic ring of o-cresol leads to compounds such as hydroxy, dihydroxy, and trihydroxy methyl benzoquinones and dihydroxy, trihydroxy, tetrahydroxy, and pentahydroxy toluenes. These products are detected in the gas phase by chemical ionization mass spectrometry (CIMS) and in the particle phase using offline direct analysis in real time mass spectrometry (DART-MS). Our data suggest that the yield of trihydroxy toluene from dihydroxy toluene is substantial. While an exact yield cannot be reported as authentic standards are unavailable, we find that a yield for trihydroxy toluene from dihydroxy toluene of ~ 0.7 (equal to the yield of dihydroxy toluene from o-cresol) is consistent with experimental results for o-cresol oxidation under low-NO conditions. These results suggest that even though the cresol pathway accounts for only ~ 20 % of the oxidation products of toluene, it is the source of a significant fraction (~ 20–40 %) of toluene secondary organic aerosol (SOA) due to the formation of low-volatility products.

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.

scholarly journals Formation of highly oxygenated low-volatility products from cresol oxidation

2017 ◽  
Vol 17 (5) ◽  
pp. 3453-3474 ◽  
Author(s):  
Rebecca H. Schwantes ◽  
Katherine A. Schilling ◽  
Renee C. McVay ◽  
Hanna Lignell ◽  
Matthew M. Coggon ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Ring Opening ◽  
Chemical Ionization ◽  
First Generation ◽  
Direct Analysis ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Ionization Mass ◽  
Particle Phase

Abstract. Hydroxyl radical (OH) oxidation of toluene produces ring-retaining products: cresol and benzaldehyde, and ring-opening products: bicyclic intermediate compounds and epoxides. Here, first- and later-generation OH oxidation products from cresol and benzaldehyde are identified in laboratory chamber experiments. For benzaldehyde, first-generation ring-retaining products are identified, but later-generation products are not detected. For cresol, low-volatility (saturation mass concentration, C* ∼ 3.5  ×  104 − 7.7  ×  10−3 µg m−3), first- and later-generation ring-retaining products are identified. Subsequent OH addition to the aromatic ring of o-cresol leads to compounds such as hydroxy, dihydroxy, and trihydroxy methyl benzoquinones and dihydroxy, trihydroxy, tetrahydroxy, and pentahydroxy toluenes. These products are detected in the gas phase by chemical ionization mass spectrometry (CIMS) and in the particle phase using offline direct analysis in real-time mass spectrometry (DART-MS). Our data suggest that the yield of trihydroxy toluene from dihydroxy toluene is substantial. While an exact yield cannot be reported as authentic standards are unavailable, we find that a yield for trihydroxy toluene from dihydroxy toluene of ∼ 0.7 (equal to the reported yield of dihydroxy toluene from o-cresol; Olariu et al., 2002) is consistent with experimental results for o-cresol oxidation under low-NO conditions. These results suggest that even though the cresol pathway accounts for only ∼ 20 % of the oxidation products of toluene, it is the source of a significant fraction (∼ 20–40 %) of toluene secondary organic aerosol (SOA) due to the formation of low-volatility products.

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;

scholarly journals Formaldehyde production from isoprene oxidation across NO<sub><i>x</i></sub> regimes

2015 ◽  
Vol 15 (21) ◽  
pp. 31587-31620 ◽  
Author(s):  
G. M. Wolfe ◽  
J. Kaiser ◽  
T. F. Hanisco ◽  
F. N. Keutsch ◽  
J. A. de Gouw ◽  
...  
Keyword(s):  
First Generation ◽  
Transport Model ◽  
Peroxy Radical ◽  
Oxidation Products ◽  
Peroxy Radicals ◽  
Chemical Transport Model ◽  
Mixing Ratios ◽  
Urban Rural ◽  
Isoprene Oxidation ◽  
Southeast Us

Abstract. The chemical link between isoprene and formaldehyde (HCHO) is a strong, non-linear function of NOx (= NO + NO2). This relationship is a linchpin for top-down isoprene emission inventory verification from orbital HCHO column observations. It is also a benchmark for overall mechanism performance with regard to VOC oxidation. Using a comprehensive suite of airborne in situ observations over the Southeast US, we quantify HCHO production across the urban-rural spectrum. Analysis of isoprene and its major first-generation oxidation products allows us to define both a "prompt" yield of HCHO (molecules of HCHO produced per molecule of freshly-emitted isoprene) and the background HCHO mixing ratio (from oxidation of longer-lived hydrocarbons). Over the range of observed NOx values (roughly 0.1–2 ppbv), the prompt yield increases by a factor of 3 (from 0.3 to 0.9 ppbv ppbv−1), while background HCHO increases by more than a factor of 2 (from 1.5 to 3.3 ppbv). We apply the same method to evaluate the performance of both a global chemical transport model (AM3) and a measurement-constrained 0-D chemical box model. Both models reproduce the NOx dependence of the prompt HCHO yield, illustrating that models with updated isoprene oxidation mechanisms can adequately capture the link between HCHO and recent isoprene emissions. On the other hand, both models under-estimate background HCHO mixing ratios, suggesting missing HCHO precursors, inadequate representation of later-generation isoprene degradation and/or under-estimated hydroxyl radical concentrations. Moreover, we find that the total organic peroxy radical production rate is essentially independent of NOx, as the increase in oxidizing capacity with NOx is largely balanced by a decrease in VOC reactivity. Thus, the observed NOx dependence of HCHO mainly reflects the changing fate of organic peroxy radicals.

scholarly journals Global simulations of monoterpene-derived peroxy radical fates and the distributions of highly oxygenated organic molecules (HOM) and accretion products

2021 ◽  
Author(s):  
Ruochong Xu ◽  
Joel A. Thornton ◽  
Ben H. Lee ◽  
Yanxu Zhang ◽  
Lyatt Jaeglé ◽  
...  
Keyword(s):  
Rate Constants ◽  
First Generation ◽  
Transport Model ◽  
Peroxy Radical ◽  
Organic Aerosol ◽  
Laboratory Studies ◽  
Chemical Transport Model ◽  
Cross Reactions ◽  
Formation Kinetics ◽  
The Impact

Abstract. We evaluate monoterpene-derived peroxy radical (MT-RO2) unimolecular autoxidation and self and cross reactions with other RO2 in the GEOS-Chem global chemical transport model. Formation of associated highly oxygenated organic molecule (HOM) and accretion products are tracked in competition with other bimolecular reactions. Autoxidation is the dominant fate up to 6–8 km for first-generation MT-RO2 which can undergo unimolecular H-shifts. Reaction with NO can be a more common fate for H-shift rate constants < 0.1 s−1 or at altitudes higher than 8 km due to the imposed Arrhenius temperature dependence of unimolecular H-shifts. For MT-derived HOM-RO2, generated by multi-step autoxidation of first-generation MT-RO2, reaction with other RO2 is predicted to be the major fate throughout most of the boreal and tropical forested regions, while reaction with NO dominates in temperate and subtropical forests of the Northern Hemisphere. The newly added reactions result in ~4 % global average decrease of HO2 and RO2 mainly due to faster self-/cross-reactions of MT-RO2, but the impact upon HO2/OH/NOx abundances is only important in the planetary boundary layer (PBL) over portions of tropical forests. Within the bounds of formation kinetics and HOM photochemical lifetime constraints from laboratory studies, predicted HOM concentrations in MT-rich regions and seasons reach 10 % or even exceed total organic aerosol as predicted by the standard GEOS-Chem model. Comparisons to observations reveal large uncertainties remain for key reaction parameters and processes, especially the photochemical lifetime of HOM and associated accretion products. Using the highest reported yields and H-shift rate constants of MT-RO2 that undergo autoxidation, HOM concentrations tend to exceed the limited set of observations. Similarly, we infer that RO2 cross reactions rate constants near the gas-kinetic limit with accretion product branching greater than ~0.25 are inconsistent with total organic aerosol unless there is rapid decomposition of accretion products, the accretion products have saturation vapor concentrations > > 1 μg m−3, or modeled MT emission rates are overestimated. This work suggests further observations and laboratory studies related to MT-RO2 derived HOM and gas-phase accretion product formation kinetics, and especially their atmospheric fate, such as gas-particle partitioning, multi-phase chemistry, and net SOA formation, are needed.

scholarly journals Atmospheric β-Caryophyllene-Derived Ozonolysis Products at Interfaces

2018 ◽  
Author(s):  
Ariana Gray Bé ◽  
Hilary M. Chase ◽  
Liu, Yangdongliu ◽  
Mary Alice Upshur ◽  
Zhang, Yue ◽  
...  
Keyword(s):  
Gas Phase ◽  
Structural Information ◽  
High Surface ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Laboratory Studies ◽  
Sum Frequency ◽  
Sum Frequency Generation Spectroscopy ◽  
Surface Active ◽  
Cloud Activation

<p>By integrating organic synthesis, secondary organic aerosol synthesis and collection, DFT calculations, and vibrational sum frequency generation spectroscopy, we identify close spectral matches between the surface vibrational spectra of β-caryophyllene-derived secondary organic material and those of β-caryophyllene aldehyde and β-caryophyllonic acid at various interfaces. Combined with the record high surface tension depression described previously for these same oxidation products, we discuss possibilities for an intrinsically chemical origin for cloud activation by terpene-derived surfactants. Although the present study does not unequivocally identify the synthesized and analyzed oxidation products on the β-caryophyllenederived SOM surfaces, these two compounds appear to be the most surface active out of the series, and have also been foci of previous β-caryophyllene field and laboratory studies.</p><p>An orientation analysis by phase-resolved SFG spectroscopy reveals a “pincer-like” configuration of the β-caryophyllene oxidation products, albeit on a model quartz surface, that somewhat resembles the orientation of inverse double-tailed surfactants at the surfaces biological systems. The structural information suggests that the less polar moiety of a surface-localized oxidation product, such as those studied here, may be the first site-of-contact for a gas-phase molecule approaching an SOA particle containing surface-active β-caryophyllene oxidation products.</p>

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