Α-pinene Ozonolysis Research Articles

Ozonolysis of α-pinene and β-pinene: Kinetics and mechanism

A combined quantum-chemical and RRKM/ME (ME--master equation) approach is employed to investigate the structures, energetics, and kinetics of intermediate and stable species, and the yields of stabilized carbonyl oxides and OH radicals from the alpha-pinene and beta-pinene ozonolysis reactions. The cycloaddition of O(3) is highly exothermic, with the reaction energies of 55.1 and 51.1 kcal mol(-1) for alpha- and beta-pinenes, respectively. Cleavage of primary ozonides yields carbonyl oxides with the barrier height of 12.2-17.5 kcal mol(-1). For the prompt reactions of carbonyl oxides from alpha- and beta-pinene ozonolysis, H migration to hydroperoxides represents the dominant pathway over ring closure to dioxiranes. The kinetic calculations indicate a significant portion of stabilization for alpha- and beta-carbonyl oxides. The yields of stabilized carbonyl oxides are estimated to be 0.34 for alpha-pinene and 0.22 for beta-pinene. The applicability of theoretical methods for investigation of oxidation reactions of large hydrocarbon molecules is demonstrated.

Alpha-pinene oxidation by OH: simulations of laboratory experiments

Abstract. This paper presents a state-of-the-art gas-phase mechanism for the degradation of α-pinene by OH and its validation by box model simulations of laboratory measurements. It is based on the near-explicit mechanisms for the oxidation of α-pinene and pinonaldehyde by OH proposed by Peeters and co-workers. The extensive set of α-pinene photooxidation experiments performed in presence as well as in absence of NO by Nozière et al. (1999a) is used to test the mechanism. The comparison of the calculated vs measured concentrations as a function of time shows that the levels of OH, NO, NO2 and light are well reproduced in the model. Noting the large scatter in the experimental results as well as the difficulty to retrieve true product yields from concentrations data, a methodology is proposed for comparing the model and the data. The model succeeds in reproducing the average apparent yields of pinonaldehyde, acetone, total nitrates and total PANs in the experiments performed in presence of NO. In absence of NO, pinonaldehyde is fairly well reproduced, but acetone is largely underestimated. The dependence of the product yields on the concentration of NO and α-pinene is investigated, with a special attention on the influence of the multiple competitions of reactions affecting the peroxy radicals in the mechanism. We show that the main oxidation channels differ largely according to photochemical conditions. E.g. the pinonaldehyde yield is estimated to be about 10% in the remote atmosphere and up to 60% in very polluted areas. We stress the need for additional theoretical/laboratory work to unravel the chemistry of the primary products as well as the ozonolysis and nitrate-initiated oxidation of α-pinene.

Low-Molecular-Weight and Oligomeric Components in Secondary Organic Aerosol from the Ozonolysis of Cycloalkenes and α-Pinene

The composition of secondary organic aerosol (SOA) from the ozonolysis of C5−C8 cycloalkenes and α-pinene, as well as the effects of hydrocarbon precursor structure and particle-phase acidity on SOA formation, have been investigated by a series of controlled laboratory chamber experiments. A liquid chromatography−mass spectrometer and an ion trap mass spectrometer are used concurrently to identify and to quantify SOA components with molecular weights up to 1600 Da. Diacids, carbonyl-containing acids, diacid alkyl esters, and hydroxy diacids are the four major classes of low-molecular-weight (MW < 250 Da) components in the SOA; together they comprise 42−83% of the total SOA mass, assuming an aerosol density of 1.4 g/cm3. In addition, oligomers (MW > 250 Da) are found to be present in all SOA. Using surrogate standards, it is estimated that the mass fraction of oligomers in the total SOA is at least 10% for the cycloalkene systems (with six or more carbons) and well over 50% for the α-pinene system. Higher seed particle acidity is found to lead to more rapid oligomer formation and, ultimately, to higher SOA yields. Because oligomers are observed to form even in the absence of seed particles, organic acids produced from hydrocarbon oxidation itself may readily promote acid catalysis and oligomer formation. The distinct effects of carbon numbers, substituent groups, and isomeric structures of the precursor hydrocarbons on the composition and yield of SOA formed are also discussed.

Coating of soot and (NH 4) 2SO 4 particles by ozonolysis products of α-pinene

The ozonolysis of α-pinene in a large aerosol chamber was used to generate secondary organic aerosol (SOA) mass by homogeneous nucleation, or by heterogeneous nucleation, either on soot, or on (NH 4) 2SO 4 seed aerosols. The rate of the α-pinene + ozone reaction and the aerosol yield of ∼19% are in good agreement with literature data. The organic coating of soot particles leads to a compaction of the fractal agglomerates expressed by an increase in fractal dimension from 1.9 to 2.1 for Diesel soot, and from 2.0 to 2.3 for spark generated “Palas” soot. The dielectric coating of the soot particles with SOA layers between 2 to 11 nm gives rise to a substantial enhancement of their single scattering albedo, from about 0.2 to 0.5, and increases the effective absorption coefficients of both soot types by ca. 30%. The coating of both soot types increases the hygroscopic growth factors (HGF) to values close below the HGF measured for pure SOA material d/ d 0∼1.12 at 90% RH.

Effect of OH radicals, relative humidity, and time on the composition of the products formed in the ozonolysis of α-pinene

The gas-phase ozonolysis of α-pinene at ppb levels were studied and the effects of OH radicals formed in the reaction, the relative humidity (RH), and time on the products formed were investigated. ...

Gas-phase ozonolysis of α-pinene: gaseous products and particle formation

Abstract The gas-phase ozonolysis of α -pinene has been studied in a stopped-flow system at 295±2 K and 950 mbar of synthetic air as well as under flow conditions at 295±0.5 K and 1000 mbar of synthetic air. Gaseous products were analyzed using on-line GC-MS/FID and FT-IR measurements. The formation of new particles ( d p⩾3 nm ) was followed by means of a differential mobility particle sizer system and an ultra-fine condensation particle counter. First, the reaction of OH radicals with c -hexane was reinvestigated. Products were c -hexanol with a yield of 0.35±0.06 and c -hexanone with a yield of 0.53±0.06. The rate coefficients of the consecutive reaction of OH radicals with c -hexanol and c -hexanone of (2.7±0.4)×10 −11 and (6.1±0.9)×10 −12 cm 3 molecule −1 s −1 , respectively, were obtained. From the reaction of OH radicals with c -hexanol, a c -hexanone yield of 0.58±0.07 was observed. Using the c -hexane scavenger technique, an OH radical yield of 0.68±0.10 was measured for the reaction of O 3 with α -pinene applicable for H 2 O concentrations of ∼1.5×10 15 and 2.6×10 17 molecule cm −3 . The formation yield of pinonaldehyde was found to be strongly dependent on the experimental conditions. Generally, the pinonaldehyde yield decreased for increasing α -pinene conversion. In the presence of an OH radical scavenger, maximum pinonaldehyde yields were 0.42±0.05 and 0.32±0.04 for [H 2 O]∼1.5×10 15 and 2.6×10 17 molecule cm −3 , respectively. Under the present conditions the pinonaldehyde formation cannot be described via the reaction of a Criegee intermediate with H 2 O. This finding is corroborated by measurements of the co-product H 2 O 2 . The formation yield of α -pinene oxide of 0.03±0.015 was unaffected by experimental conditions. Newly formed particles were measured for a relatively wide range of experimental conditions. Particle formation was only detectable for an α -pinene conversion above 3×10 11 molecule cm −3 . The results of the present study suggest that the formation of new particles from the pure O 3 + α -pinene reaction is unlikely under atmospheric conditions.

A study of the gas-phase ozonolysis of terpenes: the impact of radicals formed during the reaction

The gas-phase ozonolysis of α-pinene, Δ 3-carene and limonene was investigated at ppb levels and the impact of the ozone, relative air humidity (RH), and time was studied using experimental design. The amounts of terpene reacted varied in the different settings and were as high as 8.1% for α-pinene, 10.9% for Δ 3-carene and 23.4% for limonene. The designs were able to describe almost all the variation in the experimental data and were also successful in predicting omitted values. The results described the effects of time and ozone and also showed that RH did not have a statistically significant effect on the ozonolysis. The results also showed that all three terpenes were affected by an additional oxidation of OH radicals and/or other reactive species. The results from the designs states that this additional oxidation was responsible for 40% of the total amount of α-pinene reacted, 33% of the total amount of Δ 3-carene reacted and 41% of the total amount of limonene reacted at the settings 20 ppb terpene, 75 ppb ozone, 20% RH and a reaction time of 213 s. Additional experiments with 2-butanol as OH radical scavenger showed that the reaction with OH radicals was responsible for 37% of the total α-pinene reacted and 39% of the total Δ 3-carene reacted at the same settings. The scavenger experiments also showed that there were no significant amounts of OH radicals formed during the ozonolysis of limonene. The results from the designs were also compared to a mathematical model in order to evaluate further the data.

On-line measurements of α-pinene ozonolysis products using an atmospheric pressure chemical ionisation ion-trap mass spectrometer

An on-line technique to investigate complex organic oxidation reactions in environmental chamber experiments is presented. The method is based on the direct introduction of the chamber air into an atmospheric pressure ion source of a commercial ion-trap mass spectrometer. To demonstrate the analytical potential of the method (atmospheric pressure chemical ionisation/mass spectrometry, APCI/MS), the ozonolysis of α-pinene was investigated in a series of experiments performed in various sized reaction chambers at atmospheric pressure and 296 K in synthetic air. Investigations were focussed on the influence of the water vapour concentration on the formation of the predominant oxidation product, pinonaldehyde, derived from the α-pinene/ozone reaction. Quantification of pinonaldehyde was achieved by conducting a standard addition technique. The molar yield of pinonaldehyde was found to depend strongly on the actual water vapour concentration between <1 and 80% relative humidity. Starting with an average yield of 0.23±0.05 at dry conditions, pinonaldehyde formation was approximately doubled by reaching a yield of 0.53±0.05 at a relative humidity of around 60%. Furthermore, the formation mechanism of pinonaldehyde was investigated in greater detail using isotopically labelled water. Applying on-line APCI/MS, pinonaldehyde formation under incorporation of 18O was observed, strongly supporting the reaction of the stabilised Criegee radical with water in the gas phase as suggested by Alvarado et al. (Journal of Geophysical Research 103 (1998) 25541–25551). Furthermore, the mass spectra recorded on-line were used to perform a semi-quantitative estimation of the decomposition pathway of the primary ozonide, indicating a branching ratio of 0.35/0.65.

The aida soot aerosol campaign 1999: Dynamics and optical properties of pure and mixed aerosols

With the participation of 8 Austrian, German, and Swiss institutes an intensive soot aerosol campaign was organised in October 1999 at the 84 m 3 large aerosol chamber AIDA of the research centre in Karlsruhe (FZK). The goal of the campaign was a comprehensive physical and chemical characterisation of spark generated (Palas) soot in comparison with real Diesel soot from a commercial engine, of ammonium sulphate aerosol, and of their mixtures, as function of ageing time. Additionally, some of these aerosols were coated with organics by in situ ozonolysis of α-pinene. The following questions were addressed: May spark generated soot be used as a proxy of real combustion soot, and if so: which properties are comparable, and which are significantly different? How does mixing of Diesel soot aerosol with ammonium sulphate aerosol affect soot detection schemes, e.g. by aethalometry? How does ageing (i.e. the transition from externally to internally mixed) affect the relevant properties of soot / ammonium sulphate aerosol? How are the optical and hygroscopic properties of soot aerosol affected by an organic coating? In all cases, different methods to determine soot mass concentrations were intercompared. This paper presents an overview of the campaign, and summarises the results of model calculations with the COSIMA aerosol code, describing the time evolution and optical properties of the aerosol ensembles studied.

Development and application of a possible mechanism for the generation of cis-pinic acid from the ozonolysis of α- and β-pinene

Recent experimental studies have identified cis-pinic acid (a C 9 dicarboxylic acid) as a condensed-phase product of the ozonolysis of both α- and β-pinene, and it is currently believed to be the most likely degradation product leading to the prompt formation of new aerosols by nucleation. The observed timescale of aerosol formation appears to require that cis-pinic acid is a first-generation product, and a possible mechanism for its formation has therefore been developed. The key step in the proposed mechanism requires that the isomerisation of a complex C 9 acyl-oxy radical by a 1,7 H atom shift is able to compete with the alternative decomposition to CO 2 and a C 8 organic radical: ▪ Thermodynamic and kinetic arguments are presented, on the basis of semi-empirical electronic structure calculations, which support this proposed mechanism, and thereby the competition between the two pathways. The transfer of the labile aldehydic H atom is shown to be especially facile in this case because it occurs though an unstrained transition state; this feature can in turn be attributed to the cis-substitution of the four-membered ring, which enforces the steric proximity of the acyl-oxy and aldehyde groups. The mechanism can explain the formation of cis-pinic acid from both α- and β-pinene, because the acyl-oxy radical is likely to be formed following the decomposition of excited Criegee biradicals formed in both systems. It is also possible that a similar isomerisation reaction of a complex C 10 α-carbonyl oxy radical by a 1,8 H atom shift might explain the very recently observed formation of cis-10-hydroxy-pinonic acid from α-pinene ozonolysis, and this possibility is also explored. An existing detailed scheme describing the degradation of α-pinene (part of the Master Chemical Mechanism, MCM) is updated to include the proposed cis-pinic acid and cis-10-hydroxy-pinonic acid formation mechanisms, and the values of several uncertain parameters are adjusted on the basis of reported yields of a series of organic products from the ozonolysis of α-pinene. The updated degradation scheme is incorporated into a boundary layer box model, and representative ambient concentrations of the organic acids and other oxygenated products are calculated for a range of representative conditions appropriate to the boundary layer over central Europe. The simulated concentrations of the organic acids in general, and cis-pinic acid in particular, are strongly dependent on the level of NO X , and suggest that new aerosol formation from the oxidation of α-pinene is likely to be more favoured at lower NO X levels.

Formation of new particles in the gas-phase ozonolysis of monoterpenes

The formation of organic acids and secondary organic aerosol in the gas-phase ozonolysis was investigated by laboratory experiments at 295±2 K in the absence of seed aerosol for a series of monoterpenes ( β-pinene, sabinene, α-pinene, Δ 3-carene, limonene, terpinolene) and methylene- cyclo-hexane and methyl- cyclo-hexene as model compounds. In the filter samples of the aerosol produced by ozonolysis series of organic acids were identified as methyl ester using GC/MS. In the ozonolysis of β-pinene, sabinene, α-pinene, Δ 3-carene and limonene the corresponding C 9-dicarboxylic acids were found as main products of the organic acid fraction. In case of terpinolene, methylene- cyclo-hexane and methyl- cyclo-hexene C 7- and C 6-dicarboxylic acids, respectively, were detected. The yields of these dicarboxylic acids were determined to range between 1 and 5 mol% using ion chromatography. Particle formation was observed with a 10 nm condensation nuclei counter after the consumption of (6.1±0.3)×10 10 molecule cm −3 of β-pinene, sabinene, α-pinene, Δ 3-carene and limonene, respectively. In case of terpinolene, methylene- cyclo-hexane and methyl- cyclo-hexene (1.8±0.1)×10 11 molecule cm −3 of the reactants were converted. Upper limits for the partial vapor pressures of the dicarboxylic acids in the aerosol were determined to be (5.6±4.0)×10 −8 Torr for the C 9-dicarboxylic acids and (1.7±1.2)×10 −7 Torr for the C 7- and C 6-dicarboxylic acids. The formation of secondary organic aerosol by ozonolysis of terpenes under suitable atmospheric conditions has most likely to be taken into account.

Cis-pinic acid, a possible precursor for organic aerosol formation from ozonolysis of α-pinene

A method for the analysis of carboxylic acids in aerosols was developed, based on the collection of particles on Teflon filters (2.5 cm diameter with a 0.4 μm pore size), extraction with dichloromethane, and derivatization with BF 3-methanol followed by analysis of the formed methylesters by large-volume injection GC/MS. In aerosol samples from smog chamber experiments with α-pinene and ozone, this method was applied and resulted in the identification for the first time of cis-pinic acid. Yields were in the range of 1-3% for 1000 pbbv α-pinene reacted with 750 pbbv ozone, and in in the range of 0.3-0.5% for 100 pbbv α-pinene reacted with 75 pbbv ozone. Being a dicarboxylic acid this product is estimated to possess an extremely low vapour pressure and may thus be an important element in gas-to-particle conversion of α-pinene.