Gas-phase Reactions Of Ozone Research Articles

Estimation of mechanistic parameters in the gas-phase reactions of ozone with alkenes for use in automated mechanism construction

Abstract. Reaction with ozone is an important atmospheric removal process for alkenes. The ozonolysis reaction produces carbonyls and carbonyl oxides (Criegee intermediates, CI), which can rapidly decompose to yield a range of closed shell and radical products, including OH radicals. Consequently, it is essential to accurately represent the complex chemistry of Criegee intermediates in atmospheric models in order to fully understand the impact of alkene ozonolysis on atmospheric composition. A mechanism construction protocol is presented which is suitable for use in automatic mechanism generation. The protocol defines the critical parameters for describing the chemistry following the initial reaction, namely the primary carbonyl/CI yields from the primary ozonide fragmentation, the amount of stabilisation of the excited CI, the unimolecular decomposition pathways, rates and products of the CI, and the bimolecular rates and products of atmospherically important reactions of the stabilised CI (SCI). This analysis implicitly predicts the yield of OH from the alkene–ozone reaction. A comprehensive database of experimental OH, SCI and carbonyl yields has been collated using reported values in the literature and used to assess the reliability of the protocol. The protocol provides estimates of OH, SCI and carbonyl yields with root mean square errors of 0.13 and 0.12 and 0.14, respectively. Areas where new experimental and theoretical data would improve the protocol and its assessment are identified and discussed.

Product investigation of the gas phase ozonolysis of 1-penten-3-ol, cis-2-penten-1-ol and trans-3-hexen-1-ol

Abstract It is well known that the ozonolysis of organic compounds leads to the formation of oxygenated products, which can increase the oxidizing ability of the atmosphere. In this work, the products of the gas phase reactions of ozone with three unsaturated alcohols: 1-penten-3-ol (1P3OL), cis-2-penten-1-ol (c-2P1OL) and trans-3-hexen-1-ol (t-3H1OL) were investigated. The products formation yields were determined at 298 K and 760 Torr, in dry condition, in a 63 L pyrex reactor. The analysis of the products was performed in situ using Fourrier transform infrared (FTIR) spectroscopy (ie technique) and solid phase microextraction sampling in conjunction with gas chromatography coupled to mass spectrometry (SPME/GC-MS) (ie technique). The average yields of primary products were (in %): formaldehyde (62 ± 12) and 2-hydroxybutanal (46 ± 10) for the reaction of O3 with 1-penten-3-ol; glycolaldehyde (56 ± 14) and propanal (40 ± 10) for the reaction of O3 with cis-2-penten-1-ol; propanal (63 ± 8) and 3-hydroxypropanal (43 ± 10) for the reaction of O3 with trans-3-hexen-1-ol. As for secondary products, their average yields were (in %): propanal (12 ± 4) and acetaldehyde (10 ± 4) for the ozonolysis of 1-penten-3-ol; acetaldehyde (13 ± 5), 2-hydroxypropanal (10 ± 2) and methylglyoxal (3 ± 1) for the ozonolysis of cis-2-penten-1-ol, acetaldehyde (30 ± 4), glycolaldehyde (16 ± 4) and methylglyoxal (8 ± 3) for the ozonolysis of trans-3-hexen-1-ol. The obtained yields were compared to the values available in literature. Based on the results obtained in this study, plausible reaction mechanisms of the ozonolysis of these unsaturated alcohols have been proposed.

Temperature dependent kinetic study of the gas phase reaction of ozone with 1-penten-3-ol, cis-2-penten-1-ol and trans-3-hexen-1-ol: Experimental and theoretical data

C5 and C6 unsaturated alcohols are a family of biogenic volatile organic compounds (BVOC) emitted in the atmosphere from vegetation in response to their injuries. In this work, we report the first temperature dependent rate constants for the reaction of three unsaturated alcohols: 1-penten-3-ol (1P3OL), cis-2-penten-1-ol (c-2P1OL) and tran-3-hexen-1-ol (t-3H1OL) with ozone in a pyrex reactor coupled to a FTIR spectrometer and to a GC/MS at four different temperatures (273, 298, 313 and 333 K), at atmospheric pressure, using a relative method. The Arrhenius expressions obtained are (cm3 molecule−1 s−1):The studied reactions were also explored theoretically using computational methods based on quantum chemical theory characterizing the intermediates, transition states and the subsequent formation of reaction products. The rate constants were calculated at room temperature employing a modified transition-state theory (MTST). Both results obtained experimentally and theoretically, were discussed in terms of structure-reactivity relationships and temperature dependence. Tropospheric lifetimes of the investigated species with respect to ozone are calculated. The obtained results showed that these species are not persistent towards ozonolysis process.

Reaction of ionised steryl esters with ozone in the gas phase.

Cholesterol is an ubiquitous membrane lipid, that also serves as a precursor to many steroid hormones. The 5,6 carbon-carbon double bond on the tetracyclic carbon backbone of cholesterol is an attractive target for ozone with the reaction giving rise to a wide range of possibly bioactive molecules. Despite this, little is known about the ozonolysis of cholesterol esters, which often possess an additional double bond(s) on the fatty acyl chain. Understanding the intrinsic gas phase reaction of ozone with the two disparate double bond positions on cholesteryl esters can inform our understanding of these processes in vivo, particularly reactions occurring at the air-water interface (e.g., tear film lipid layer) and on the surfaces of the body where these cholesterol and cholesteryl esters may be present (e.g., sebum). In the present work we describe the gas phase ozonolysis of lithium and sodium cations formed from three steryl esters: two isomeric for double bond position (cholestanyl oleate and cholesteryl stearate), and a third with carbon-carbon double bonds present in both the sterol ring system and fatty acyl chain (cholesteryl oleate). We confirm the enhanced reactivity of the endocyclic carbon-carbon double bond with ozone over double bonds present in the acyl chain, and elucidate competitive interactions between the two double bond positions during ozonolysis. Elucidation of the mechanisms underlying this interaction is important for both understanding these processes in vivo and for deploying ozonolysis chemistry in analytical strategies for lipidomics.

Kinetic and mechanistic study on gas phase reactions of ozone with a series ofcis-3-hexenyl esters

Reaction kinetics of O3with fourcis-3-hexenyl esters were studied using experimental methods in a flow tube reactor as well as using theoretical methods.

Kinetic and Mechanistic Studies for the Gas-phase Reaction of Ozone with 2, 3-Dimethyl-2-Butene and 1, 3-Butadiene

The reactions of ozone with 2,3-Dimethyl-2-Butene (CH3)2C=C(CH3)2 and 1,3-Butadiene CH2=CHCH=CH2 have been investigated under atmospheric conditions at 298±3K in air using both relative and absolute rate techniques, and the measured rate coefficients are found to be in good agreement in both techniques used. The obtained results show the addition of ozone to the double bond in these compounds and how it acts as function of the methyl group substituent situated on the double bond. The yields of all the main products have been determined using FTIR and GC-FID and the product studies of these reactions establish a very good idea for the decomposition pathways for the primary formed compounds (ozonides) and give a good information for the effect of the methyl group on the degradation pathways. The results have been discussed from the view point of their importance in the atmospheric oxidation of these pollutants.

Molecular dynamics simulation of gas-phase ozone reactions with sabinene and benzene

Gas-phase reactions of ozone (O3) with volatile organic compounds were investigated both by experiment and molecular simulations. From our experiments, it was found ozone readily reacts with VOC pure components and reduces it effectively. By introducing ozone intermittently, the reaction between VOC and ozone is markedly enhanced. In order to understand the relationship between intermediate reactions and end products, ozone reaction with benzene and alicyclic monoterpene sabinene were simulated via a novel hybrid quantum mechanical/molecular mechanics (QM/MM) algorithm that forced repeated bimolecular collisions. Molecular orbital (MO) rearrangements (manifested as bond dissociation or formation), resulting from the collisions, were computed by semi-empirical unrestricted Hartree-Fock methods (e.g., RM1). A minimum of 975 collisions between ozone and targeted organic species were performed to generate a distribution of reaction products. Results indicated that benzene and sabinene reacted with ozone to produce a range of stable products and intermediates, including carbocations, ring-scission products, as well as peroxy (HO2 and HO3) and hydroxyl (OH) radicals. Among the stable sabinene products observed included formaldehyde and sabina-ketone, which have been experimentally demonstrated in gas-phase ozonation reactions. Among the benzene ozonation products detected composed of oxygen mono-substituted aromatic C6H5O, which may undergo further transformation or rearrangement to phenol, benzene oxide or 2,4-cyclohexadienone; a phenomenon which has been experimentally observed in vapor-phase photocatalytic ozonation reactions.

Gas-Phase Ozonolysis of Cycloalkenes: Formation of Highly Oxidized RO2 Radicals and Their Reactions with NO, NO2, SO2, and Other RO2 Radicals.

The gas-phase reaction of ozone with C5-C8 cycloalkenes has been investigated in a free-jet flow system at atmospheric pressure and a temperature of 297 ± 1 K. Highly oxidized RO2 radicals bearing at least 5 O atoms in the molecule and their subsequent reaction products were detected in most cases by means of nitrate-CI-APi-TOF mass spectrometry. Starting from a Criegee intermediate after splitting-off an OH-radical, the formation of these RO2 radicals can be explained via an autoxidation mechanism, meaning RO2 isomerization (ROO → QOOH) and subsequently O2 addition (QOOH + O2 → R'OO). Time-dependent RO2 radical measurements concerning the ozonolysis of cyclohexene indicate rate coefficients of the intramolecular H-shifts, ROO → QOOH, higher than 1 s(-1). The total molar yield of highly oxidized products (predominantly RO2 radicals) from C5-C8 cycloalkenes in air is 4.8-6.0% affected with a calibration uncertainty by a factor of about two. For the most abundant RO2 radical from cyclohexene ozonolysis, O,O-C6H7(OOH)2O2 ("O,O" stands for two O atoms arising from the ozone attack), the determination of the rate coefficients of the reaction with NO2, NO, and SO2 yielded (1.6 ± 0.5) × 10(-12), (3.4 ± 0.9) × 10(-11), and <10(-14) cm(3) molecule(-1) s(-1), respectively. The reaction of highly oxidized RO2 radicals with other peroxy radicals (R'O2) leads to detectable accretion products, RO2 + R'O2 → ROOR' + O2, which allows to acquire information on peroxy radicals not directly measurable with the nitrate ionization technique applied here. Additional experiments using acetate as the charger ion confirm conclusively the existence of highly oxidized RO2 radicals and closed-shell products. Other reaction products, detectable with this ionization technique, give a deeper insight in the reaction mechanism of cyclohexene ozonolysis.

Radical Product Yields from the Ozonolysis of Short Chain Alkenes under Atmospheric Boundary Layer Conditions

The gas-phase reaction of ozone with unsaturated volatile organic compounds (VOCs), alkenes, is an important source of the critical atmospheric oxidant OH, especially at night when other photolytic radical initiation routes cannot occur. Alkene ozonolysis is also known to directly form HO2 radicals, which may be readily converted to OH through reaction with NO, but whose formation is poorly understood. We report a study of the radical (OH, HO2, and RO2) production from a series of small alkenes (propene, 1-butene, cis-2-butene, trans-2-butene, 2-methylpropene, 2,3-dimethyl-2-butene (tetramethyl ethene, TME), and isoprene). Experiments were performed in the European Photoreactor (EUPHORE) atmospheric simulation chamber, with OH and HO2 levels directly measured by laser-induced fluorescence (LIF) and HO2 + ΣRO2 levels measured by peroxy-radical chemical amplification (PERCA). OH yields were found to be in good agreement with the majority of previous studies performed under comparable conditions (atmospheric pressure, long time scales) using tracer and scavenger approaches. HO2 yields ranged from 4% (trans-2-butene) to 34% (2-methylpropene), lower than previous experimental determinations. Increasing humidity further reduced the HO2 yields obtained, by typically 50% for an RH increase from 0.5 to 30%, suggesting that HOx production from alkene ozonolysis may be lower than current models suggest under (humid) ambient atmospheric boundary layer conditions. The mechanistic origin of the OH and HO2 production observed is discussed in the context of previous experimental and theoretical studies.

Gas-Phase Ozonolysis of Selected Olefins: The Yield of Stabilized Criegee Intermediate and the Reactivity toward SO2

The gas-phase reaction of ozone with olefins represents an important path for the conversion of unsaturated hydrocarbons in the atmosphere. The current interest is focused on the formation of stabilized Criegee intermediates (sCI) and possible further reactions of sCI. We report results from the ozonolysis of 2,3-dimethyl-2-butene (TME), trans-2-butene and 1-methyl-cyclohexene (MCH) carried out in an atmospheric pressure flow tube at 293 ± 0.5 K and RH = 50% using chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometry to detect H2SO4 produced from SO2 oxidation by sCI. The yields of sCI were found to be in good agreement with recently observed data: 0.62 ± 0.28 (TME), 0.53 ± 0.24 (trans-2-butene) and 0.16 ± 0.07 (MCH). The rate coefficients for sCI + SO2 from our experiment, (0.9–7.7) × 10–13 cm3 molecule–1 s–1, are within the range of recommendations from indirect determinations as given so far in the literature. Our study helps to assess the importance of sCI in atmospheric chemistry, especially for the oxidation of SO2 to H2SO4.

Total radical yields from tropospheric ethene ozonolysis

The gas-phase reactions of ozone with alkenes can be significant sources of free radicals (OH, HO(2) and RO(2)) in the Earth's atmosphere. In this study the total radical production and degradation products from ethene ozonolysis have been measured, under conditions relevant to the troposphere, during a series of detailed simulation chamber experiments. Experiments were carried out in the European photoreactor EUPHORE (Valencia, Spain), utilising various instrumentation including a chemical-ionisation-reaction time-of-flight mass-spectrometer (CIR-TOF-MS) measuring volatile organic compounds/oxygenated volatile organic compounds (VOCs/OVOCs), a laser induced fluorescence (LIF) system for measuring HO(2) radical products and a peroxy radical chemical amplification (PERCA) instrument measuring HO(2) + ΣRO(2). The ethene + ozone reaction system was investigated with and without an OH radical scavenger, in order to suppress side reactions. Radical concentrations were measured under dry and humid conditions and interpreted through detailed chemical chamber box modelling, incorporating the Master Chemical Mechanism (MCMv3.1) degradation scheme for ethene, which was updated to include a more explicit representation of the ethene-ozone reaction mechanism.The rate coefficient for the ethene + ozone reaction was measured to be (1.45 ± 0.25) × 10(-18) cm(3) molecules(-1) s(-1) at 298 K, and a stabilised Criegee intermediate yield of 0.54 ± 0.12 was determined from excess CO scavenger experiments. An OH radical yield of 0.17 ± 0.09 was determined using a cyclohexane scavenger approach, by monitoring the formation of the OH-initiated cyclohexane oxidation products and HO(2). The results highlight the importance of knowing the [HO(2)] (particularly under alkene limited conditions and high [O(3)]) and scavenger chemistry when deriving radical yields. An averaged HO(2) yield of 0.27 ± 0.07 was determined by LIF/model fitting. The observed yields are interpreted in terms of branching ratios for each channel within the postulated ethene ozonolysis mechanism.

Rate Constants for the Gas Phase Reactions of Ozone with Diethylamine and Triethylamine

Kinetics of the reactions of ozone with diethylamine (DEA) and triethylamine (TEA) were investigated in a self-made Teflon chamber.Experiments were conducted under pseudo-first-order decay conditions using excess DEA and TEA.Cyclohexane was added to the reactor to quench OH radicals.At (298±1) K and 1.01×105 Pa, the measured absolute rate constants were (1.33±0.15)×10-17 cm3·molecule-1·s-1 for DEA and (8.20±1.01)×10-17 cm3·molecule-1·s-1 for TEA.Comparing our results with data for the reactions of analogous amines with ozone, we propose that the amines react with ozone probably through an electrophilic reaction mechanism.In addition, the reactions of trialkylamines with ozone are all much faster than those of dialkylamines with ozone, which may explain the intriguing finding in several field studies where higher concentrations of dialkylammonium were detected in aerosol samples.The atmospheric lifetimes of DEA and TEA were also estimated based on the measured rate constants and the ambient tropospheric concentration of ozone, which indicates that the reaction with ozone is an important loss pathway for these amines in the atmosphere, especially in polluted areas.

Rate constants for the gas phase reaction of ozone with n-butyl acrylate and ethyl methacrylate

Rate constants for the reaction of ozone with n-butyl acrylate (BUAC) and ethyl methacrylate (ETMEAC) have been investigated for the first time. At 293 ± 1 K and atmospheric pressure, the measured values were (2.40 ± 0.29) × 10 −18 cm 3 molecule −1 s −1 for BUAC and (7.68 ± 0.88) × 10 −18 cm 3 molecule −1 s −1 for ETMEAC. The atmospheric lifetimes have also been estimated, which indicate that only in the polluted areas could reaction with ozone be one of the important sinks for these unsaturated esters.

The gas-phase ozonolysis of β-caryophyllene (C15H24). Part I: an experimental study

The gas phase reaction of ozone with beta-caryophyllene was investigated in a static glass reactor at 750 Torr and 296 K under various experimental conditions. The reactants and gas phase products were monitored by FTIR-spectroscopy and proton-transfer-reaction mass spectrometry (PTR-MS). Aerosol formation was monitored with a scanning mobility particle sizer (SMPS) and particulate products analysed by liquid chromatography/mass spectrometry (HPLC-MS). The different reactivity of the two double bonds in beta-caryophyllene was probed by experiments with different ratios of reactants. An average rate coefficient at 295 K for the first-generation products was determined as 1.1 x 10(-16) cm(3) molecule(-1) s(-1). Using cyclohexane as scavenger, an OH-radical yield of (10.4 +/- 2.3)% was determined for the ozonolysis of the more reactive internal double bond, whereas the average OH-radical yield for the ozonolysis of the first-generation products was found to be (16.4 +/- 3.6)%. Measured gas phase products are CO, CO(2) and HCHO with average yields of (2.0 +/- 1.8)%, (3.8 +/- 2.8)% and (7.7 +/- 4.0)%, respectively for the more reactive internal double bond and (5.5 +/- 4.8)%, (8.2 +/- 2.8)% and (60 +/- 6)%, respectively from ozonolysis of the less reactive double bond of the first-generation products. The residual FTIR spectra indicate the formation of an internal secondary ozonide of beta-caryophyllene. From experiments using HCOOH as a Criegee intermediate (CI) scavenger, it was concluded that at least 60% of the formed CI are collisionally stabilized. The aerosol yield in the ozonolysis of beta-caryophyllene was estimated from the measured particle size distributions. In the absence of a CI scavenger the yield ranged between 5 and 24%, depending on the aerosol mass. The yield increases with addition of water vapour or with higher concentrations of formic acid. In the presence of HCHO, lower aerosol yields were observed. This suggests that HCOOH adds to a Criegee intermediate to form a low-volatility compound responsible for aerosol formation. The underlying reaction mechanisms are discussed and compared with the results from the accompanying theoretical paper.

Stomatal uptake and stomatal deposition of ozone in isoprene and monoterpene emitting plants

Volatile isoprenoids were reported to protect plants against ozone. To understand whether this could be the result of a direct scavenging of ozone by these molecules, the stomatal and non-stomatal uptake of ozone was estimated in plants emitting isoprene or monoterpenes. Ozone uptake by holm oak (Quercus ilex, a monoterpene emitter) and black poplar (Populus nigra, an isoprene emitter) was studied in whole plant enclosures (continuously stirred tank reactors, CSTR). The ozone uptake by plants was estimated measuring ozone concentration at the inlet and outlet of the reactors, after correcting for the uptake of the enclosure materials. Destruction of ozone at the cuticle or at the plant stems was found to be negligible compared to the ozone uptake through the stomata. For both plant species, a relationship between stomatal conductance and ozone uptake was found. For the poplar, the measured ozone losses were explained by the uptake of ozone through the stomata only, and ozone destruction by gas phase reactions with isoprene was negligible. For the oak, gas phase reactions of ozone with the monoterpenes emitted by the plants contributed significantly to ozone destruction. This was confirmed by two different experiments showing a) that in cases of high stomatal conductance but under low CO(2) concentration, a reduction of monoterpene emission was still associated with reduced O(3) uptake; and b) that ozone losses due to the gas phase reactions only can be measured when using the exhaust from a plant chamber to determine the gas phase reactivity in an empty reaction chamber. Monoterpenes can therefore relevantly scavenge ozone at leaf level contributing to protection against ozone.

The gas-phase ozonolysis of unsaturated volatile organic compounds in the troposphere

The gas-phase reactions of ozone with unsaturated hydrocarbons are significant sources of free radical species (including *OH) and particulate material in the Earth's atmosphere. In this tutorial review, the kinetics, products and mechanisms of these reactions are examined, starting with a discussion of the original mechanism proposed by Criegee and following with a summary presentation of the complex, free radical-mediated reactions of carbonyl oxide (Criegee) intermediates. The contribution of ozone-terpene reactions to the atmospheric burden of secondary organic aerosol material is also discussed from the viewpoint of the formation of non-volatile organic acid products from the complex chemistry of ozone with alpha-pinene. Throughout the article, currently accepted understanding is supported through the presentation of key experimental results, and areas of persistent or new uncertainty are highlighted.

Rate constant of the gas phase reaction of dimethyl sulfide (CH 3SCH 3) with ozone

The gas phase reaction of ozone with dimethyl sulfide (DMS) has been studied in our self-made chamber. Experiments were conducted under supposedly pseudo-first-order decay conditions, keeping [DMS] 0 > 10[O 3] 0, but having different combinations of [DMS] 0 and [O 3] 0. Cyclohexane was added into the reactor to eliminate the effect of OH radicals. A value of (1.04 ± 0.21) × 10 −19 cm 3 molecule −1 s −1 for rate constant was obtained under room temperature of about 301 K. The wall effects and the role of cyclohexane are discussed. Our results enrich the kinetics data of atmospheric chemistry, and further confirm that the gas phase reaction of DMS with ozone is not important for the loss of DMS in the atmosphere.

Ozonolysis Fragment Quenching by Nitrate Formation: The Pressure Dependence of Prompt OH Radical Formation

The gas-phase reaction of ozone with alkenes is known to be a significant source of OH radicals in the troposphere. The pressure dependence of the OH yield in ozone−alkene reactions is both important and controversial; the poor understanding of the pressure-dependent OH yield for different ozone−alkene reactions is a major obstacle to developing an accurate simulation of tropospheric chemistry. Using a high-pressure flow reactor, we have investigated the ozonolysis of a series of alkenes in the presence of NO2. The four alkenes studied were 2,3-dimethyl-2-butene (TME), trans-5-decene, cyclohexene, and α-pinene, which provide significant differences in size (C6 vs C10) and structure (linear vs cyclic) to elucidate the influence of these competing effects on OH formation. OH yields from TME and trans-5-decene ozonolysis decrease with increasing pressure, but OH yields from cyclohexene (0.64 ± 0.20) and α-pinene (0.89 ± 0.20) are pressure-independent and consistent with the literature. Acetone production increases relative to TME consumption as pressure increases; this observation, supported by density functional calculations, is consistent with acetone and nitrate radical production from the SCI + NO2 reaction. Both the pressure dependence of OH formation from the linear alkenes (TME and trans-5-decene) and the pressure-independent OH yields observed for cyclohexene and α-pinene can be explained by changes in the extent of collisional stabilization of the carbonyl oxide (Criegee) intermediate with increasing pressure.

Reaction of α-cedrene with ozone: mechanism, gas and particulate products distribution

Abstract The gas-phase reaction of ozone with α-cedrene ( I ) in the absence and presence of an OH radical scavenger (cyclohexane) has been studied in the outdoor 25 m 3 Teflon film chambers at the UNC smog chamber facility. Twenty-two compounds were identified for the first time in this study. Important products identified and semi-quantified were α-cedronaldehyde ( VI ), α-cedronic acid ( VIII ), α-cedrinic acid ( X ), α-norcedronaldehyde ( VII ), 8-hydroxy-9-α-cedranone ( III ), and α-norcedronic acid ( IX ). Acetone, formaldehyde, and acetaldehyde also were identified in this study. On average, measured gas and particle phase products accounted for ∼56% of the reacted α-cedrene. The total yield of products bearing hydroxy groups (e.g. 8-hydroxy-9-α-cedranone ( III )) and aldehydes (e.g. α-cedronaldehyde ( VI ), α-norcedronaldehyde ( VII )) was found to be slightly dependent on the presence of an OH radical scavenger. Generally, the aldehyde yield was found to be higher when cyclohexane was present, and the hydroxy compounds yield was higher when cyclohexane was absent. All products identified in this study were found in the particle phase. α-Cedrinic acid ( X ), α-cedronic acid ( VIII ), and α-cedronaldehyde (VI) were observed in the early stage in the aerosol phase and may play an important role in the early formation of SOA. Detailed reaction schemes leading to most reaction products observed here are presented and discussed.

A theoretical study of the reactions of carbonyl oxide with water in atmosphere: the role of water dimer

Carbonyl oxide is a well-known intermediate formed in gas-phase reactions of ozone with alkenes. Secondary reactions of carbonyl oxide are suggested to lead to the formation of HO, H 2O 2 and organic peroxides in the atmosphere. We performed a theoretical study of reactions of carbonyl oxide with water and a water dimer. Using CCSD(T)/6-311+G(2d,2p)//B3LYP/6-311+G(2d,2p) calculations we found that the most energetically favourable channel is the formation of hydroxymethyl hydroperoxide (HMHP) as the result of reactions of carbonyl oxide with the water dimer. The potential importance of water dimer reactions in the chemistry of the troposphere is discussed herein.