Campholenic aldehyde ozonolysis: a mechanism leading to specific biogenic secondary organic aerosol constituents

In the present study, campholenic aldehyde ozonolysis was performed to investigate pathways leading to specific biogenic secondary organic aerosol (SOA) marker compounds. Campholenic aldehyde, a known α-pinene oxidation product, is suggested to be a key intermediate in the formation of terpenylic acid upon α-pinene ozonolysis. It was reacted with ozone in the presence and absence of an OH radical scavenger, leading to SOA formation with a yield of 0.75 and 0.8, respectively. The resulting oxidation products in the gas and particle phases were investigated employing a denuder/filter sampling combination. Gas-phase oxidation products bearing a carbonyl group, which were collected by the denuder, were derivatised by 2,4-dinitrophenylhydrazine (DNPH) followed by liquid chromatography/negative ion electrospray ionisation time-of-flight mass spectrometry analysis and were compared to the gas-phase compounds detected by online proton-transfer-reaction mass spectrometry. Particle-phase products were also analysed, directly or after DNPH derivatisation, to derive information about specific compounds leading to SOA formation. Among the detected compounds, the aldehydic precursor of terpenylic acid was identified and its presence was confirmed in ambient aerosol samples from the DNPH derivatisation, accurate mass data, and additional mass spectrometry (MS² and MS³ fragmentation studies). Furthermore, the present investigation sheds light on a reaction pathway leading to the formation of terpenylic acid, involving α-pinene, α-pinene oxide, campholenic aldehyde, and terpenylic aldehyde. Additionally, the formation of diaterpenylic acid acetate could be connected to campholenic aldehyde oxidation. The present study also provides insights into the source of other highly functionalised oxidation products (e.g. <i>m</i> / <i>z</i> 201, C₉H₁₄O₅ and <i>m</i> / <i>z</i> 215, C₁₀H₁₆O₅), which have been observed in ambient aerosol samples and smog chamber-generated monoterpene SOA. The <i>m</i> / <i>z</i> 201 and 215 compounds were tentatively identified as a C₉- and C₁₀-carbonyl-dicarboxylic acid, respectively, based on reaction mechanisms of campholenic aldehyde and ozone, as well as detailed interpretation of mass spectral data, in conjunction with the formation of corresponding DNPH derivatives

Particle‐Phase Uptake and Chemistry of Highly Oxygenated Organic Molecules (HOMs) From α‐Pinene OH Oxidation

Secondary organic aerosol (SOA) forms a major part of the tropospheric submicron particle mass. Still, the exact formation mechanisms of SOA have remained elusive. It is now admitted that highly oxygenated organic molecules (HOMs) can contribute to a large fraction of SOA formation. In this study, we performed a set of chamber experiments to investigate the SOA formation, and the HOMs uptake and processing directly formed by OH‐radical initiated oxidation of α‐pinene under two different aerosol seed conditions. Numerous HOM compounds were identified using advanced online and offline analytical techniques, and grouped into four classes according to their different uptake behaviors. For the first time, individual HOMs uptake coefficients ranging from 1.1 × 10−2 to 1.5 × 10−1 were experimentally determined and analyzed using a resistance model which considers uptake limitations by individual gas‐ and/or particle‐phase processes. This study demonstrates that the uptake coefficients of HOMs strongly depend on their molar mass and their respective O/C ratio. Results show that aerosol seed composition and phase state affect the initial uptake of HOMs. Furthermore, the study demonstrates that the acidity and/or different seed phase‐state can significantly enhance the subsequent uptake through occurring acidity‐driven reactions reflected in a reactive behavior, particularly under (NH4)HSO4 seed conditions, promoting up to 3 times a higher SOA mass formation including the formation of highly oxidized organosulfates (HOOS). Overall, the present study implies that HOMs and their subsequent chemical processing can play an important role in both the early growth of newly formed particles and SOA formation when particle acidity is high.Plain Language Summary: Tropospheric organic aerosol (OA) compounds represent a large part of submicron particulate matter. A big fraction of OA is formed from oxidation of emitted gaseous volatile organic compounds such as α‐pinene. Oxidation products are less‐volatile compounds that tend to condense on aerosol particles. Recently identified “highly oxygenated organic molecules” (HOMs) are formed by gas‐phase autoxidation processes and exhibit very low vapor pressures. Therefore, HOMs are expected to efficiently contribute to secondary organic aerosol (SOA). However, up to now, SOA formation potential of HOMs is still not well described because of lacking experimental investigations and analysis. Consequently, this study aims to investigate the mentioned HOMs partitioning and subsequent SOA formation from the OH‐radical initiated oxidation of α‐pinene under both Na2SO4 and (NH4)HSO4 aerosol seed conditions through complex chamber experiments. For the first time, individual HOMs uptake coefficients were determined experimentally. Further investigations demonstrated that the uptake coefficients of HOMs strongly depend on their molar mass, as well as on their respective O/C ratio. Finally, the results show that aerosol acidity and/or phase state significantly enhances the HOMs uptake and promotes up to three times higher SOA mass formation under (NH4)HSO4 seed conditions compared to that under neutral seed conditions.Key Points: Uptake coefficients of numerous highly oxygenated organic molecules (HOMs) were experimentally determined for the first time. HOMs uptake and secondary organic aerosol formation were significantly enhanced by acidic (NH4)HSO4 seed. Highly oxidized organosulfates formation were observed under acidic (NH4)HSO4 seed conditions.European Commission http://dx.doi.org/10.13039/501100000780National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809https://doi.org/10.25326/FJNF-7224https://doi.org/10.25326/KC8N-DY5

Terpenylic acid and related compounds: precursors for dimers in secondary organic aerosol from the ozonolysis of α- and β-pinene

In the present study, we have characterized the structure of a higher-molecular weight (MW) 358 α- and β-pinene dimeric secondary organic aerosol (SOA) product that received ample attention in previous molecular characterization studies and has been elusive. Based on mass spectrometric evidence for deprotonated molecules formed by electrospray ionization in the negative ion mode and chemical considerations, it is suggested that diaterpenylic acid is a key monomeric intermediate for dimers of the ester type. It is proposed that cis-pinic acid is esterified with the hydroxyl-containing diaterpenylic acid, which can be explained through acid-catalyzed hydrolysis of the recently elucidated lactone-containing terpenylic acid and/or diaterpenylic acid acetate, both first-generation oxidation products. To a minor extent, higher-MW 358 and 344 diester products are formed containing other terpenoic acids as monomeric units, i.e., diaterpenylic acid instead of cis-pinic acid, and diaterebic acid instead of diaterpenylic acid. It is shown that the MW 358 diester and related MW 344 compounds, which can be regarded as processed SOA products, also occur in ambient fine (PM2.5) rural aerosol collected at night during the warm period of the 2006 summer field campaign conducted at K-puszta, Hungary, a rural site with coniferous vegetation. This indicates that, under ambient conditions, the higher-MW diesters are formed in the particle phase over a longer time-scale than that required for gas-to-particle partitioning of their monomeric precursors in laboratory α-/β-pinene ozonolysis experiments

Effect of varying experimental conditions on the viscosity of <i>α</i>-pinene derived secondary organic material

Knowledge of the viscosity of particles containing secondary organic material (SOM) is useful for predicting reaction rates and diffusion in SOM particles. In this study we investigate the viscosity of SOM particles as a function of relative humidity and SOM particle mass concentration, during SOM synthesis. The SOM was generated via the ozonolysis of <i>α</i>-pinene at &lt; 5 % relative humidity (RH). Experiments were carried out using the poke-and-flow technique, which measures the experimental flow time (<i>τ</i>_{exp, flow}) of SOM after poking the material with a needle. In the first set of experiments, we show that <i>τ</i>_{exp, flow} increased by a factor of 3600 as the RH increased from &lt; 0.5 RH to 50 % RH, for SOM with a production mass concentration of 121 µg m⁻³. Based on simulations, the viscosities of the particles were between 6  ×  10⁵ and 5  ×  10⁷ Pa s at &lt; 0.5 % RH and between 3  ×  10² and 9  ×  10³ Pa s at 50 % RH. In the second set of experiments we show that under dry conditions <i>τ</i>_{exp, flow} decreased by a factor of 45 as the production mass concentration increased from 121 to 14 000 µg m⁻³. From simulations of the poke-and-flow experiments, the viscosity of SOM with a production mass concentration of 14 000 µg m⁻³ was determined to be between 4  ×  10⁴ and 1.5  ×  10⁶ Pa s compared to between 6  ×  10⁵ and 5  ×  10⁷ Pa s for SOM with a production mass concentration of 121 µg m⁻³. The results can be rationalized by a dependence of the chemical composition of SOM on production conditions. These results emphasize the shifting characteristics of SOM, not just with RH and precursor type, but also with the production conditions, and suggest that production mass concentration and the RH at which the viscosity was determined should be considered both when comparing laboratory results and when extrapolating these results to the atmosphere

High spin polarization at the HERA electron storage ring

This paper describes the progress made in 1992 towards increasing the vertical electron beam polarization at HERA. Utilizing harmonic spin-orbit corrections and beam tuning, the vertical polarization has been increased from 15% to nearly 60% at a beam energy of 26.7 GeV. The long-term reproducibility of the polarization is excellent. Measurements of the build-up time and the energy dependence of the polarization are also described

High spin polarization at the HERA electron storage ring

This paper describes the progress made in 1992 towards increasing the vertical electron beam polarization at HERA. Utilizing harmonic spin-orbit corrections and beam tuning, the vertical polarization has been increased from 15% to nearly 60% at a beam energy of 26.7 GeV. The long-term reproducibility of the polarization is excellent. Measurements of the build-up time and the energy dependence of the polarization are also described