Tesi sul tema "Aqueous aerosols"

Récemment, les états triplets des espèces organiques ont attiré l'attention en tant qu'oxydants potentiellement importants dans les environnements aqueux, en concurrence avec l'oxygène singulet et les radicaux OH. Tout d'abord, la thèse étudie des extraits d'échantillons d'aérosols, en hiver et en été, pour leurs concentrations à l'état d'équilibre et les rendements quantiques des trois principaux oxydants : les états triplets, l'oxygène singulet et les radicaux OH. Nos résultats montrent que si l'on considère à la fois les concentrations à l'état d'équilibre et les constantes de vitesse du second ordre pour les oxydants avec différentes classes d'espèces organiques, les états triplets seront dans la plupart des cas l'oxydant dominant. La thèse présente également les résultats préliminaires d'une étude en collaboration qui examine les méthodes de normalisation des mesures du rendement quantique de l'oxygène singulet. L'étude suivante de cette thèse a porté sur l'examen de la composition massique de l'un des échantillons d'aérosol. Cet échantillon a été analysé par spectrométrie de masse à haute résolution avant et après son irradiation. Les principaux résultats montrent qu'au cours du vieillissement, des espèces plus importantes se sont formées. Un substitut, la vanilline, a été choisi pour étudier les voies de dégradation des espèces d'aérosols et a montré un grand nombre de produits après l'irradiation. L'effet de l'irradiation de la vanilline à 6 degree C a montré une augmentation de la quantité d'espèces avec des nombres de carbone plus importants, tels que les espèces C23. Les espèces C23 ont été attribuées à des trimères de vanilline. Enfin, la production de radicaux OH à partir d'espèces à l'état triplet a été étudiée en phase aqueuse. La formation d'OH à partir de sources connues de radicaux OH, NO3- et H2O2, a été comparée à celle de la vanilline et du 4-hydroxybenzaldéhyde, qui ont été utilisés comme indicateurs des espèces organiques présentes dans les aérosols aqueux (et les nuages/brouillards). Une étude bibliographique des concentrations des sources d'OH dans les aérosols et les nuages/brouillards a été compilée et utilisée en combinaison avec les taux de formation d'OH. A partir de ces estimations, il est clair que les états triplets pourraient potentiellement avoir des taux de formation d'OH qui sont de 1 à 2 ordres de grandeur plus élevés que NO3- et H2O2. Dans l'ensemble, cette thèse fournit des résultats qui illustrent l'importance des états triplets dans les aérosols aqueux, et le fait qu'ils peuvent être sous-estimés en tant qu'oxydants pour les espèces organiques et en tant que sources de radicaux OH
Recently, triplet states of organic species have gained attention as oxidants that are potentially important in aqueous environments, competing with singlet oxygen and OH radicals. Firstly, the thesis investigates extracts of aerosol samples, from winter and summer time, for their steady-state concentrations and quantum yields of the three main oxidants: triplet states, singlet oxygen, and OH radicals. Our findings show that when considering both steady-state concentrations and second-order rate constants for the oxidants with various classes of organic species, the triplet states will in most cases be the dominant oxidant. The thesis also show preliminary results of a collaborating study that investigates methods for standardizing singlet oxygen quantum yield measurements. The next study of this thesis involved the examination of the mass composition of one of the aerosol samples. This sample was analyzed using high resolution mass spectrometry before and after the sample was irradiated. Main results show that during aging larger species were formed. A proxy, vanillin, was chosen to investigate the degradation pathways of aerosol species, and showed a large number of products after irradiation. The effect of irradiating vanillin at 6 degree C showed an increased amount of species with larger carbon numbers, such as C23 species. The C23 species were attributed to trimers of vanillin. Lastly, the OH radical production from triplet state species were investigated in the aqueous phase. The OH formation from known sources of OH radicals, NO3- and H2O2, were compared to that of vanillin and 4-hydroxybenzaldehyde, which were applied for proxies of organic species present in aqueous aerosols (and clouds/fog). A literature study of concentrations of the OH sources in aerosols and cloud/fog was compiled and used in combination with the OH formation rates. From these estimations, it was clear that triplet states could potentially have OH formation rates that are 1-2 orders of magnitude larger than NO3- and H2O2. Overall, this thesis provides results that illustrates the importance of triplet states in the aqueous aerosols, and that they may be underestimated as both oxidants for organic species and as sources of OH radicals

The quantification of the hygroscopic properties of atmospheric aerosols is important to understand several processes they are involved in, such as clouds formation, their interaction with solar radiation and the penetration of particles in the human respiratory track. In addition, the interaction of deposited aerosols with surfaces depends on their physical state, too; thus, characterizing their phase transitions as a function of their chemical composition is key to understanding the effects they have on materials (e.g. printed circuits, cultural heritage artifacts). In order to investigate the hygroscopic properties of aerosols, an electrical conductance method in an Aerosol Exposure Chamber was developed for the determination of the phase transitions of PM2.5 aerosol samples during relative humidity cycles. The obtained Deliquescence and Crystallization Relative Humidity (DRH and CRH) were put in relation with the ionic chemical composition of the analyzed samples: it was found that seasonal chemical variations result in seasonal trends for DRH and CRH, too. The implications of these results for Free-Cooled Data Centers, for the understanding of the role of particles in stone-decay processes of cultural heritage artifacts and for the common algorithms used in the remote sensing of particulate matter concentrations were evaluated. The ionic fraction characterisation was also used as an input for a state-of-the-art equilibrium aerosol model (E-AIM) to simulate the DRH of the samples. Some discrepancies were evidenced in the comparison of experimental and modelled values, because the hygroscopic properties of the organic components need to be included too. In order to effectively account for their contribute, current aerosol models need to be refined with accurate hygroscopicity measurements on organic compounds of increasing molecular complexity and their mixtures with common electrolytes. Such measurements are essential for understanding and modelling the microphysical properties that determine the partitioning of water between the gas and the aerosol phases in chemically complex systems. In this context, an experimental technique based on evaporation kinetics measurements in an Cylindrical Electrodynamic Balance was developed for the measurement of hygroscopic properties on single confined droplets from aqueous solutions with known chemical composition. To expand the range of applicability of a previously developed technique to water activities from 0.5 to values close to saturation (>0.99), well-characterized binary and ternary inorganic mixtures were considered. The obtained results were used to successfully validate this technique by comparing them with calculations from E-AIM model and to assess the sensitivity of this technique to small changes in chemical composition. The first class of atmospherically relevant compounds that was considered was aminium sulphates, which are the products of the neutralization reactions of sulphuric acid and short-chained alkylamines (methyl- and ethylamines). They have been detected in atmospheric aerosols up to hundreds of pg m-3, but their hygroscopic behaviour was less characterized than their inorganic equivalent, ammonium sulphate, even if they can promote cloud droplets formation and particle growth.

Thesis (Ph. D.)--California Institute of Technology, 1988. UM #88-03,381.
Advisor names found in the Acknowledgments pages of the thesis. Title from home page. Viewed 02/19/2010. Includes bibliographical references.

Aerosols affect climate change, the energy balance of the atmosphere, and public health due to their variable chemical composition, size, and shape. Aerosols from natural and anthropogenic sources can be primary organic aerosols (POA), which are directly emitted to the atmosphere, or secondary organic aerosols (SOA) that are formed from chemical reactions of gas-phase precursors. At variance with the well investigated formation of SOA from gas phase precursors, the chemistry of aqueous SOAs that contribute to the total SOA budget remains unknown. Field measurements have revealed that carboxylic, dicarboxylic and oxocarboxylic acids are abundant species present in SOAs. This thesis explores the fate of two such acids, pyruvic (PA) and glyoxylic (GA) acids surrogates of the oxocarboxylic acids in the atmosphere, in their cross reaction under solar irradiation and dark thermal aging. Mixtures of complex photoproducts are identified by ion chromatography (IC) with conductivity and electrospray (ESI) mass spectrometry (MS) detection, direct ESI-MS analysis in the negative ion mode, and nuclear magnetic resonance spectroscopy (NMR) analysis including one-dimensional (1H- and 13C-NMR) and two-dimensional techniques such as gradient correlation spectroscopy (gCOSY) and heteronuclear single quantum correlation (HSQC). A reaction mechanism for the cross reaction is provided based on all experimental observations.

Thesis (M.S.)--West Virginia University, 1998.
Title from document title page. Document formatted into pages; contains xii, 136 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 131-132).

Atmospheric aerosol particles influence our planet's climate and contribute to poor air quality, increased mortality and degraded visibility. Central to these issues is how atmospheric aerosol particles interact with gas species to affect chemistry and cloud formation. Recent research shows that some aqueous solutions relevant to atmospheric aerosol (notably secondary organic material, which constitutes a large mass fraction of atmospheric aerosol particles) can be highly viscous and can behave mechanically like a solid. This has led to suggestions that these particles exist out of equilibrium with the gas phase in the atmosphere, with implications for heterogeneous chemistry and ice nucleation. In order to quantify any kinetic limitations, it is vital to have quantitative data about the diffusion of various relevant species within these materials. This thesis describes the direct measurement and application of water diffusion coefficients in aqueous solutions relevant to atmospheric aerosol, including sucrose and secondary organic material. A water diffusion model is developed, validated and used with a new parameterisation of the water diffusion coefficient in secondary organic material to quantify the rate of uptake and loss of water from aerosol particles. It is shown that, although this material can behave mechanically like a solid, at 280 K water diffusion is not kinetically limited on timescales of 1 s for atmospheric-sized particles. This is not the case, however, for colder conditions: modelling of 100 nm particles predicts that under mid to upper tropospheric conditions radial inhomogeneities in water content produce a low viscosity surface region and more solid interior. This may significantly affect aerosol chemistry and the ability of particles to nucleate ice. Also reported are the diffusion coefficients of sucrose in aqueous sucrose at higher concentrations than have been previously investigated. These measurements provide insights into the role of organic molecules in aerosol evaporation and chemistry. Together with the diffusion coefficients of water measured in this material, they will also offer a valuable means to study the fundamental nature of diffusion in a simple but widely used material, and specifically the breakdown of the Stokes-Einstein relationship.

Cette étude se focalise sur les impacts de la réactivité en phase aqueuse de la méthacroléïne et de la méthyl vinyl cétone sur la formation des nouveaux aérosols organiques secondaires (AOS), et les impacts de la réactivité en phase aqueuse sur le vieillissement des AOS formés par l’isoprène, α-pinène et 1,3,5-triméthylbenzène en phase gazeuse. Les études de la réactivité en phase aqueuse ont été étudiées vis-à-vis des radicaux OH. Dans le but d’identifier et quantifier les produits d’oxydation des différents précurseurs d’intérêt, les échantillons en phase aqueuse ont été analysés par différents systèmes analytiques. Les résultats montrent clairement la formation de petits composés primaires et secondaires qui ont été expliqués par les mécanismes réactionnels. On a observé également la formation de composés à haute masse moléculaire par rapport à leurs précurseurs. Ces produits ont été supposés être très peu volatils et pourraient induire la formation des AOS lors de l’évaporation de l’eau. Leur capacité à former des AOS a été montrée expérimentalement par les expériences de nébulisation des solutions aqueuses à différents temps de réaction. Les résultats montrent qu’au moins une part de ces produits à haute masse moléculaire reste en phase particulaire lors de l’évaporation de l’eau, et contribue à la formation des AOS. L’ensemble de ces résultats met en évidence le fait que la réactivité en phase aqueuse atmosphérique peut induire des effets importants sur la formation et le vieillissement des AOS atmosphériques, qui peut induire une modification des propriétés physico-chimiques des aérosols
This work focused on the impacts of aqueous phase OH-oxidation of methacrolein, methyl vinyl ketone on the SOA formation, and impacts of aqueous phase OH-oxidation on aging of SOA that are formed by isoprene, -pinene and 1,3,5-trimethylbenzene in gas phase. The chemical characterization of aqueous phase was performed by different analytical techniques. The results show the formation of small primary and secondary reaction products that were explained by suitable chemical reaction mechanisms. The formation of oligomers with high molecular mass (compared with their precursors) has also been observed during the OH-oxidation. These oligomers might be low volatile compounds that induce the formation of SOA during water evaporation. Their capacity to form SOA was experimentally demonstrated by nebulizing the aqueous phase solution at different reaction times. The results show that at least a part of oligomers remains in the particle phase during water evaporation, and contributes to the SOA formation. All of these results highlight that aqueous phase reactivity could induce important effects on the formation and aging of atmospheric SOA, which can induce modification of physico-chemical properties of SOA

Raman spectroscopy has been employed to probe the mass and heat transfer dynamics and structure of aqueous aerosol droplets. Spontaneous and stimulated Raman scattering processes have been used to determine the size, composition and temperature of multicomponent aerosol droplets. Single droplets have been interrogated using optical tweezers, and the internal microphysical droplet structure has been ascertained.

Accurate simulations of the global radiative impact of anthropogenic emissions must employ a tropospheric chemistry model that predicts realistic distributions of aerosols of all types. The need for a such a comprehensive yet computationally efficient tropospheric chemistry model is addressed in this research via systematic development of the various sub-models/mechanisms representing the gas-, aerosol-, and cloud-phase chemistries. The gas-phase model encompasses three tropospheric chemical regimes - background and urban, continental rural, and remote marine. The background and urban gas-phase mechanism is based on the paradigm of the Carbon Bond approach, modified for global-scale applications. The rural gas-phase chemistry includes highly condensed isoprene and a-pinene reactions. The isoprene photooxidation scheme is adapted for the present model from an available mechanism in the literature, while an a-pinene photooxidation mechanism, capable of predicting secondary organic aerosol formation, is developed for the first time from the available kinetic and product formation data. The remote marine gas- phase chemistry includes a highly condensed dimethylsulfide (DMS) photooxidation mechanism, based on a comprehensive scheme available in the literature. The proposed DMS mechanism can successfully explain the observed latitudinal variation in the ratios of methanesulfonic acid to non-sea-salt sulfate concentrations. A highly efficient dynamic aerosol growth model is developed for condensing inorganic gases. Algorithms are presented for calculating equilibrium surface concentrations over dry and wet multicomponent aerosols containing sulfate, nitrate, chloride, ammonium, and sodium. This alternative model is capable of predictions as accurate for completely dissolved aerosols, and more accurate for completely dry aerosols than some of the similar models available in the literature. For cloud processes, gas to liquid mass-transfer limitations to aqueous-phase reactions within cloud droplets are examined for all absorbing species by using the two-film model coupled with a comprehensive gas and aqueous-phase reaction mechanisms. Results indicate appreciable limitations only for the OH, HO2, and NO3 radicals. Subsequently, an accurate highly condensed aqueous-phase mechanism is derived for global-scale applications.
Ph. D.

Thesis: Ph. D. in Environmental Chemistry, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Atmospheric particulate matter (or "aerosol") is known to have important implications for climate change, air quality, and human health. Our ability to predict its formation and fate is hindered by uncertainties associated with one type in particular, organic aerosol (OA). Ambient OA measurements indicate that it can become highly oxidized in short timescales, but this is generally not reproduced well in laboratory studies or models, suggesting the importance of formation processes that are not fully understood at present. In this thesis, I focus on the potential for chemistry within aqueous aerosol to produce highly oxidized OA. I first use a retrosynthetic modeling approach to constrain the viable precursors and formation pathways of highly oxidized OA, starting with a target oxidized product and considering possible reverse reactions. Results suggest three general formation mechanisms are possible: (1) functionalization reactions that add multiple functional groups per oxidation step, (2) oligomerization of highly oxidized precursors, or (3) fast aging within the condensed phase, such as oxidation within aqueous particles. The focus of the remainder of the thesis involves experiments designed to study this third pathway. To examine the importance of the formation of highly oxidized OA in the aqueous phase (wet particles or cloud droplets), I investigate aqueous oxidation of polyols within submicron particles in an environmental chamber, allowing for significant gas-particle partitioning of reactants, intermediates, and products. Results are compared to those from analogous oxidation reactions carried out in bulk solution (the phase in which most previous studies were carried out). Both sets of experiments result in rapid oxidation, but substantially more carbon is lost from the submicron particles, likely due to differences in partitioning of early-generation products. Finally, OA is formed from the gas-phase ozonolysis of biogenic precursors in the presence of reactive aqueous particles, showing that oxidation within the condensed phase can generate highly oxidized products. The overall results of this thesis demonstrate that aqueous-phase oxidation can contribute to the rapid formation of highly oxidized OA and therefore its inclusion in atmospheric models should be considered, but that experiments to constrain such pathways must be carried out under atmospherically relevant conditions.
Financial support from the National Science Foundation, under grant numbers CHE-1012809 and AGS-1056225
by Kelly Elizabeth Daumit.
Ph. D. in Environmental Chemistry

Atmospheric aerosols affect climate change by altering the energy balance of the atmosphere, and public health due to their variable chemical composition, size, and shape. While the formation of secondary organic aerosol (SOA) from gas phase precursors is relatively well understood, it does not account for the abundance of SOA observed during field measurements. Recently it has become apparent that in-aerosol aqueous chemical reactions likely provide some of the missing sources of SOA production, and many studies of aqueous phase processes are underway. This work explores the fates of the simplest 2-oxocarboxylic acids, glyoxylic acid (GA) and pyruvic acid (PA), under simulated solar irradiation in the aqueous phase. Field measurements have revealed that mono-, di-, and oxocarboxylic acids are abundant species present in atmospheric waters. Of particular interest are 2-oxocarboxylic acids because their conjugated carbonyl moieties result in significant UV-visible absorption above 300 nm, allowing absorption of sunlight in the lower troposphere, thereby initiating radical photochemistry and leading to formation of SOA. In Chapter 2 of this work, GA is demonstrated to primarily undergo α-cleavage, producing CO, CO2, formic acid, and the key SOA precursor glyoxal. Trace amounts of oxalic acid and tartaric acid are also quantified. Additionally, the dark thermal aging of glyoxylic acid photoproducts, studied by UV-visible and fluorescence spectroscopies, reveals that the optical properties of the solutions are altered radically by the glyoxal produced. The optical properties display periodicity during photolytic-dark cycles, reflecting behavior expected for aerosols during nighttime and daytime cycles. In contrast, Chapter 3 shows that PA photoreacts via a proton-coupled electron transfer (PCET) mechanism that produces CO2 and organic acids of increased complexity with 6 to 8 carbons. A combination of analytical techniques including 1H and 13C NMR; 13C gCOSY NMR; mass spectrometry; chromatography; and isotope substitutions allows the organic products to be identified as: 2,3-dimethyltartaric acid; 2-hydroxy-2-((3-oxobutan-2-yl)oxy)propanoic acid; and the quasi-intermediate 2-(1-carboxy-1-hydroxyethoxy)-2-methyl-3-oxobutanoic acid. In Chapter 4, PA irradiation is also shown to consume dissolved oxygen so fast that solutions become depleted within a few minutes depending on reaction conditions. This fast process directly produces the atmospheric oxidant singlet oxygen, which enhances the oxidizing capacity of the atmosphere. Additionally, PA photochemistry only proceeds under very acidic conditions (pH ≤ 3.5), like those in most atmospheric aerosols. Finally, we require a thorough understanding of the behavior of 2-oxocarboxylic acids at the air-water interface of aerosols because much of the GA and PA present in the atmosphere is produced in the gas phase and needs to partition into the aqueous phase to undergo photoreaction. Therefore, Chapter 5 uses surface sensitive online electrospray ionization mass spectrometry (OESI-MS) to demonstrate that carboxylic acids delivered from the gas phase onto the surface of aqueous microdroplets display enhanced acidities relative to bulk water solutions. This work demonstrates that aqueous photolysis is a very competitive atmospheric fate for both GA and PA. It also shows that these photoreactions are capable of contributing substantially to SOA formation by building chemical complexity and forming oxidants directly.

La pollution atmosphérique liée aux aérosols organiques secondaire (SOA) représente un des enjeux majeurs du XXIème siècle. La photochimie multiphasique des SOA constitue le coeur et l'originalité de cette thèse.Le réacteur photochimique permet de simuler en laboratoire, l'oxydation en phase aqueuse atmosphérique des composés organiques volatils biogéniques (BVOC), et notamment, la méthyl vinyl cétone (MVK), afin d'étudier la formation ces SOA.Nous étudions la réactivité de la MVK en présence de ●OH et sa capacité à oligomériser en fonction des concentrations initiales de MVK, d'oxygène, et de ●OH. Une large stratégie analytique basée sur la chromatographie liquide couplée à la spectrométrie de masse (MS) permet d'identifier des produits de réaction, et d'établir un mécanisme réactionnel, expliquant la formation des oligomères, leurs rendements et leur vieillissement.Les données colligées servent d'entrées à un modèle de boîte multiphasique, afin d'explorer la sensibilité de l'oligomérisation aux conditions atmosphériques.Ensuite, nous comparons la réactivité de la MVK en présence de ●OH à celle induite par la photolyse de l'acide pyruvique; puis nous mesurons la tension de surface engendrée par ces deux systèmes d'oligomères. Enfin, la mobilité ionique couplée à la MS permet d'observer la co-oligomérisation d'une gamme étendue de BVOC en présence de ●OH.L'oligomérisation atmosphérique implique (i) une concentration minimale de précurseurs pouvant être atteinte dans les aérosols humides via la co-oligomérisation; (ii) une réactivité en compétition avec l'oxygène dissous dans la phase aqueuse, et dont la pertinence atmosphérique reste à explorer
Air pollution caused by secondary organic aerosol (SOA) is one of the major challenges of this century. We focus this thesis on SOA , through an innovative approach, i.e. multiphase photochemistry.The photochemical reactor allows to simulate in laboratory, the atmospheric aqueous phase oxidation of biogenic volatile organic compounds (BVOC) and in particular, methyl vinyl ketone (MVK), and thus, to study SOA.We study the reactivity of MVK in the presence of ●OH and its ability to oligomerize under various initial concentrations of oxygen, MVK and ●OH. A wide analytical strategy based on liquid chromatography-mass spectrometry is used to identify the reaction products, and establish a chemical mechanism. We focus on these oligomers systems, formation, yield and aging. Collected data are used as inputs to a multiphase box model to explore the sensitivity of oligomerization to the variations of physical and chemical atmospheric parameters. The photochemistry of pyruvic acid generates radical chemistry and initiates MVK oligomerization. We closely compare this reaction to MVK ●OH oxidation. Then, we measure the surface activity of both systems. The ability of oligomers to partition to the interface could affect the climate. Finally, we used ion mobility - mass spectrometry to observe ●OH co-oligomerization of a mixture of organic compounds most representative of the atmosphere.Atmospheric oligomerization implies (i) a minimal concentration of precursors that could be reached in wet aerosol via the co-oligomerization; (ii) a reactivity in competition with the addition of the dissolved oxygen, whose the atmospheric relevance remains to be explored

L'aérosol atmosphérique a des effets sur le changement climatique global et un impact sanitaire non-négligeables. Dans l'aérosol atmosphérique terrestre, les composés organiques représentent une fraction importante. Du fait de l'extrême complexité de cette fraction organique et des processus dynamiques qui l'animent, une fraction non négligeable de celle-ci n'est pas clairement identifiée à ce jour malgré des techniques d'analyses toujours plus nombreuses. Dans cette thèse, nous avons voulu explorer la richesse d'information fournie par une technique innovante : la spectrométrie de masse à haute résolution (HRMS). La haute résolution du LTQ-Orbitrap fournit une extrême précision sur la masse des molécules analysées et permet d'en identifier les formules brutes. Tout d'abord, nous avons utilisé cette nouvelle méthode de caractérisation afin d'élucider en laboratoire des mécanismes de production de l'aérosol se déroulant en phase aqueuse. Associée à une caractérisation par RMN, la HRMS nous permet d'identifier des voies de fabrication de composés de faible poids moléculaires (acides carboxyliques, aldéhydes, cétone) ainsi que des composés à haut poids moléculaire : les oligomères formés se transforment en HULIS au cours de leur vieillissement. Le fait que la méthacroléine (MACR) et la méthyl-vinyl-cétone (MVK), les deux principaux produits d'oxydation de l'isoprène, forment des AOS en phase aqueuse avait été précédemment montré. Ce travail montre que les précurseurs des AOS sont différents selon l'isomère et que les séries d'oligomères formées atteignent 1400 Da.. L'étude HRMS des produits permet de proposer un mécanisme radicalaire d'oligomérisation de la MVK. L'analyse HRMS des produits de la MACR montre qu'en plus du mécanisme valable pour la MVK, la réactivité de la MACR engendre co-polymérisation et production d'Hulis. Une signature HRMS des Hulis a été mise en évidence. Ensuite, nous avons utilisé les méthodes de traitement de données HRMS pour tenter de les appliquer à l'identification d'aérosol ambiant. Les composés organiques représentent la fraction majeure des particules de l'aérosol atmosphérique ; une grande partie reste mal identifiée. Une compréhension détaillée des sources et des procédés de transformations est nécessaire. L'investigation de la composition chimique des particules de matière fine et ultrafine peut être apporter par HRMS. L'ESI-Orbitrap apporte une description moléculaire qui détermine les propriétés chimiques et physiques de l'aérosol organique. Les particules ont été échantillonnées selon leur taille respective. Les prélèvements ont été fait à Grenoble en été et en hiver. Une comparaison saisonnière permet d'identifier des signatures chimiques différentes. Enfin, une intercomparaison est établie avec des échantillons d'une troisième campagne prélevées en proximité routière: MOCOPO
Atmospheric aerosol has an important impact on the radiative balance of Earth. Organics compounds represent the major fraction of atmospheric aerosol particles; a large part is still not well characterized. A detailed understanding of the sources, transformations processes and fates of organics aerosols is needed. This work investigates the ability of the ESI-Orbitrap to characterize organics molecules of aerosol. Firstly, experimental and analytical methods were developed to unveil mechanistic ambiguities that were previously shown. Methacrolein (MACR) and methyl vinyl ketone (MVK) (the two main gas phase atmospheric oxidation products of isoprene) were known to form oligomers and secondary organic aerosol (SOA) upon aqueous phase OHoxidation and subsequent water evaporation. For the two precursors, ESI-MS analysis of the reacting solutions brought clear evidence for the formation of oligomer systems having a mass range of up to 1400 Da.. Taking advantage of the regularities observed in the oligomer systems, the ESI-HRMS data were used to propose stoichiometries for more than 75% of the observed signal. Moreover, we show here that MACR oligomers aging give rise to HULIS production. In addition, global estimates of secondary organic aerosol (SOA) formation flux show that current descriptions miss a large fraction of the sources. This gaping underestimation has been linked to a poor understanding of aerosol functionalization in the atmosphere and lead to the formation of a new conceptual framework for the description of the aerosol, based on volatility versus polarity plots. This new framework is almost exclusively based on High Resolution Time of Flight Aerosol Mass Spectrometer(HR-Tof-AMS) data, as this instrument gives access to average H:C, N:C and O:C ratios for the bulk aerosol. The AMS estimates for O:C and H:C ratios are thus based on heavy fragmentation of organics followed by stoichiometry attribution on those fragments. Given the resolution of the HR-ToF-AMS, such an attribution is not feasible above a certain mass, making fragmentation a necessary aspect of the measurement. Conversely, Orbitrap-HRMS provide a resolution of 100,000 at m/z 400, with a mass range 50 – 2000 amu, enabling stoichiometry retrieval up to higher masses than the AMS. Coupled to a “soft” electrospray ionization method, Orbitrap-HRMS gives O:C and H:C ratios on entire molecules in the analysed mixture. We used samples from three contrasted field campaigns: the two first at an urban kerbside site in summer and in winter, the third one in the roadway vicinity (Grenoble, France). Accelerated Solvent Extraction provides a clear overview of the chemical composition of organic extracts from aerosol particles collected at different season at an urban site. The elemental composition was obtained within 2-5 ppm, on the range 150-300 m/z. However, this study shows that both ionization polarity were needed to get a complete picture of the chemical composition of the samples. We showed that Esi-Orbitrap-HRMS allows to compute a statistical distribution of the elementary ratios that is different from a simple average value. Keywords: HRMS, SOA

The ubiquitous abundance of organic compounds in natural and anthorpogenically influenced eco-systems has put these compounds into the focus of atmospheric research. Organic compounds have an impact on air quality, climate, and human health. Moreover, they affect particle growth, secondary organic aerosol (SOA) formation, and the global radiation budget by altering particle properties. To investigate the multiphase chemistry of organic compounds and interactions with the aqueous phase in the troposphere, modelling can provide a useful tool. The oxidation of larger organic molecules to the final product CO2 can involve a huge number of intermediate compounds and tens of thousands of reactions. Therefore, the creation of explicit mechanisms relies on automated mechanism construction. Estimation methods for the prediction of the kinetic data needed to describe the degradation of these intermediates are inevitable due to the infeasibility of an experimental determination of all necessary data. Current aqueous phase descriptions of organic chemistry lag behind the gas phase descriptions in atmospheric chemical mechanisms despite its importance for the multiphase chemistry of organic compounds. In this dissertation, the gas phase mechanism Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) has been advanced by a protocol for the description of the oxidation of organic compounds in the aqueous phase. Therefore, a database with kinetic data of 465 aqueous phase hydroxyl radical and 129 aqueous phase nitrate radical reactions with organic compounds has been compiled and evaluated. The database was used to evaluate currently available estimation methods for the prediction of aqueous phase kinetic data of reactions of organic compounds. Among the investigated methods were correlations of gas and aqueous kinetic data, kinetic data of homologous series of various compound classes, reactivity comparisons of inorganic radical oxidants, Evans-Polanyi-type correlations, and structure-activity relationships (SARs). Evans-Polanyi-type correlations have been improved for the purpose of automated mechanism self-generation of mechanisms with large organic molecules. A protocol has been designed based on SARs for hydroxyl radical reactions and the improved Evans-Polanyi-type correlations for nitrate radical reactions with organic compounds. The protocol was assessed in a series of critical sensitivity studies, where uncertainties of critical parameters were investigated. The advanced multiphase generator GECKO-A was used to generate mechanisms, which were applied in box model studies and validated against two sets of aerosol chamber experiments. Experiments differed by the initial compounds used (hexane and trimethylbenzene) and the experimental conditions (UV-C lights off/on and additional in-situ hydroxyl radical source no/yes). Reasonable to good agreement of the modelled and experimental results was achieved in these studies. Finally, GECKO-A was used to create two new CAPRAM version, where, for the first time, branchingratios for different reaction pathways were introduced and the chemistry of compounds with up to four carbon atoms has been extended. The most detailed mechanism comprises 4174 compounds and 7145 processes. Detailed investigations were performed under real tropospheric conditions in urban and remote continental environments. Model results showed significant improvements, especially in regard to the formation of organic aerosol mass. Detailed investigations of concentration-time profiles and chemical fluxes refined the current knowledge of the multiphase processing of organic compounds in the troposphere, but also pointed at current limitations of the generator protocol, the mechanisms created, and current understanding of aqueous phase processes of organic compounds
Das zahlreiche Vorkommen organischer Verbindungen in natürlichen und anthropogen beeinflussten Ökosystemen hat diese Verbindungen in den Fokus der Atmosphärenforschung gerückt. Organische Verbindungen beeinträchtigen die Luftqualität, die menschliche Gesundheit und das Klima. Weiterhin werden Partikelwachstum und -eigenschaften, sekundäre organische Partikelbildung und dadurch der globale Strahlungshaushalt durch sie beeinflusst. Um die troposphärische Multiphasenchemie organischer Verbindungen und Wechselwirkungen mit der Flüssigphase zu untersuchen, sind Modellstudien hilfreich. Die Oxidation großer organischer Moleküle führt zu einer Vielzahl an Zwischenprodukten. Der Abbau erfolgt in unzähligen Reaktionen bis hin zum Endprodukt CO2. Bei der Entwicklung expliziter Mechanismen muss deshalb für diese Verbindungen auf computergestützte, automatisierte Methoden zurückgegriffen werden. Abschätzungsmethoden für die Vorhersage kinetischer Daten zur Beschreibung des Abbaus der Zwischenprodukte sind unabdingbar, da eine experimentelle Bestimmung aller benötigten Daten nicht realisierbar ist. Die derzeitige Beschreibung der Flüssigphasenchemie unterliegt deutlich den Beschreibungen der Gasphase in atmosphärischen Chemiemechanismen trotz deren Relevanz für die Multiphasenchemie. In dieser Arbeit wurde der Gasphasenmechanismusgenerator GECKO-A (“Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere”) um ein Protokoll zur Oxidation organischer Verbindungen in der Flüssigphase erweitert. Dazu wurde eine Datenbank mit kinetischen Daten von 465 Hydroxylradikal- und 129 Nitratradikalreaktionen mit organischen Verbindungen angelegt und evaluiert. Mit Hilfe der Datenbank wurden derzeitige Abschätzungsmethoden für die Vorhersage kinetischer Daten von Flüssigphasenreaktionen organischer Verbindungen evaluiert. Die untersuchten Methoden beinhalteten Korrelationen kinetischer Daten aus Gas- und Flüssigphase, homologer Reihen verschiedener Stoffklassen, Reaktivitätsvergleiche, Evans-Polanyi-Korrelationen und Struktur-Reaktivitätsbeziehungen. Für die Mechanismusgenerierung großer organischer Moleküle wurden die Evans-Polanyi-Korrelationen in dieser Arbeit weiterentwickelt. Es wurde ein Protokol für die Mechanismusgenerierung entwickelt, das auf Struktur-Reaktivitätsbeziehungen bei Reaktionen von organischen Verbindungen mit OH-Radikalen und auf den erweiterten Evans-Polanyi-Korrelationen bei NO3-Radikalreaktionen beruht. Das Protokoll wurde umfangreich in einer Reihe von Sensitivitätsstudien getestet, um Unsicherheiten kritischer Parameter abzuschätzen. Der erweiterte Multiphasengenerator GECKO-A wurde dazu verwendet, neue Mechanismen zu generieren, die in Boxmodellstudien gegen Aerosolkammerexperimente evaluiert wurden. Die Experimentreihen unterschieden sich sowohl in der betrachteten Ausgangssubstanz (Hexan und Trimethylbenzen) und dem Experimentaufbau (ohne oder mit UV-C-Photolyse und ohne oder mit zusätzlicher partikulärer Hydroxylradikalquelle). Bei den Experimenten konnte eine zufriedenstellende bis gute Übereinstimmung der experimentellen und Modellergebnisse erreicht werden. Weiterhin wurde GECKO-A verwendet, um zwei neue CAPRAM-Versionen mit bis zu 4174 Verbindungen und 7145 Prozessen zu generieren. Erstmals wurden Verzweigungsverhältnisse in CAPRAM eingeführt. Außerdem wurde die Chemie organischer Verbindungen mit bis zu vier Kohlenstoffatomen erweitert. Umfangreiche Untersuchungen unter realistischen troposphärischen Bedingungen in urbanen und ländlichen Gebieten haben deutliche Verbesserungen der erweiterten Mechanismen besonders in Bezug auf Massenzuwachs des organischen Aerosolanteils gezeigt. Das Verständnis der organischen Multiphasenchemie konnte durch detaillierte Untersuchungen zu den Konzentrations-Zeit-Profilen und chemischen Flüssen vertieft werden, aber auch gegenwärtige Limitierungen des Generators, der erzeugten Mechanismen und unseres Verständnisses für Flüssigphasenprozesse organischer Verbindungen aufgezeigt werden

Die chemische Zusammensetzung und die physikalischen Eigenschaften von troposphärischen Gasen, Partikeln und Wolken hängen aufgrund zahlreicher Prozesse stark voneinander ab. Insbesondere chemische Multiphasenprozesse in Wolken können die physiko-chemischen Eigenschaften der Luft und troposphärischer Partikel klein- und großräumig verändern. Diese chemische Prozessierung des troposphärischen Aerosols innerhalb von Wolken beeinflusst die chemischen Umwandlungen in der Atmosphäre, die Bildung von Wolken, deren Ausdehnung und Lebensdauer, sowie die Transmissivität von einfallender und ausgehender Strahlung durch die Atmosphäre. Damit sind wolken-chemische Prozesse relevant für das Klima auf der Erde und für verschiedene Umweltaspekte. Daher ist ein umfassendes Verständnis dieser Prozesse wichtig. Die explizite Behandlung chemischer Reaktionen in der Flüssigphase stellt allerdings eine Herausforderung für atmosphärische Computermodelle dar. Detaillierte Beschreibungen der Flüssigphasenchemie werden deshalb häufig nur für Boxmodelle verwendet. Regionale Chemie-Transport-Modelle und Klimamodelle berücksichtigen diese Prozesse meist nur mit vereinfachten chemischen Mechanismen oder Parametrisierungen. Die vorliegende Arbeit hat zum Ziel, den Einfluss der chemischer Mehrphasenprozesse innerhalb von Wolken auf den Verbleib relevanter Spurengase und Partikelbestandteile mit Hilfe des state‑of‑the‑art 3D-Chemie-Transport-Modells COSMO-MUSCAT zu untersuchen. Zu diesem Zweck wurde das Model um eine detaillierte Beschreibung chemischer Prozesse in der Flüssigphase erweitert. Zusätzlich wurde das bestehende Depositionsschema verbessert, um auch die Deposition von Nebeltropfen zu berücksichtigen. Die durchgeführten Modellerweiterungen ermöglichen eine bessere Beschreibung des troposphärischen Multiphasensystems. Das erweiterte Modellsystem wurde sowohl für künstliche 2D-Bergüberströmungsszenarien als auch für reale 3D-Simulationen angewendet. Mittels Prozess- und Sensitivitätsstudien wurde der Einfluss (i) des Detailgrades der verwendeten Mechanismen zur Beschreibung der Flüssigphasenchemie, (ii) der Größenauflösung des Tropfenspektrums und (iii) der Tropfenanzahl auf die chemischen Modellergebnisse untersucht. Die Studien belegen, dass die Auswirkungen der Wolkenchemie aufgrund ihres signifikanten Einflusses auf die Oxidationskapazität in der Gas- und Flüssigphase, die Bildung von organischer und anorganischer Partikelmasse sowie die Azidität der Wolkentropfen und Partikel in regionalen Chemie-Transport-Modellen berücksichtigt werden sollten. Im Vergleich zu einer vereinfachten Beschreibung der Wolkenchemie führt die Verwendung des detaillierten chemischen Flüssigphasenmechanismus C3.0RED zu verringerten Konzentrationen wichtiger Oxidantien in der Gasphase, einer höheren Nitratmasse in der Nacht, geringeren nächtlichen pH-Werten und einer veränderten Sulfatbildung. Darüber hinaus ermöglicht eine detaillierte Wolkenchemie erst Untersuchungen zur Bildung sekundärer organischer Partikelmasse in der Flüssigphase. Die größenaufgelöste Behandlung der Flüssigphasenchemie hatte nur geringen Einfluss auf die chemischen Modellergebnisse. Schließlich wurde das erweiterte Modell für Fallstudien zur Feldmesskampagne HCCT‑2010 genutzt. Zum ersten Mal wurde dabei ein chemischer Mechanismus mit der Komplexität von C3.0RED verwendet. Die räumlichen Effekte realer Wolken z. B. auf troposphärische Oxidantien oder die Bildung anorganischer Masse wurden untersucht. Der Vergleich der Modellergebnisse mit verfügbaren Messungen hat viele Übereinstimmungen aber auch interessante Unterschiede aufgezeigt, die weiter untersucht werden müssen
In the troposphere, a vast number of interactions between gases, particles, and clouds affect their physico-chemical properties, which, therefore, highly depend on each other. Particularly, multiphase chemical processes within clouds can alter the physico-chemical properties of the gas and the particle phase from the local to the global scale. This cloud processing of the tropospheric aerosol may, therefore, affect chemical conversions in the atmosphere, the formation, extent, and lifetime of clouds, as well as the interaction of particles and clouds with incoming and outgoing radiation. Considering the relevance of these processes for Earth\'s climate and many environmental issues, a detailed understanding of the chemical processes within clouds is important. However, the treatment of aqueous phase chemical reactions in numerical models in a comprehensive and explicit manner is challenging. Therefore, detailed descriptions of aqueous chemistry are only available in box models, whereas regional chemistry transport and climate models usually treat cloud chemical processes by means of rather simplified chemical mechanisms or parameterizations. The present work aims at characterizing the influence of chemical cloud processing of the tropospheric aerosol on the fate of relevant gaseous and particulate aerosol constituents using the state-of-the-art 3‑D chemistry transport model (CTM) COSMO‑MUSCAT. For this purpose, the model was enhanced by a detailed description of aqueous phase chemical processes. In addition, the deposition schemes were improved in order to account for the deposition of cloud droplets of ground layer clouds and fogs. The conducted model enhancements provide a better insight in the tropospheric multiphase system. The extended model system was applied for an artificial mountain streaming scenario as well as for real 3‑D case studies. Process and sensitivity studies were conducted investigating the influence of (i) the detail of the used aqueous phase chemical representation, (ii) the size-resolution of the cloud droplets, and (iii) the total droplet number on the chemical model output. The studies indicated the requirement to consider chemical cloud effects in regional CTMs because of their key impacts on e.g., oxidation capacity in the gas and aqueous phase, formation of organic and inorganic particulate mass, and droplet acidity. In comparison to rather simplified aqueous phase chemical mechanisms focusing on sulfate formation, the use of the detailed aqueous phase chemistry mechanism C3.0RED leads to decreased gas phase oxidant concentrations, increased nighttime nitrate mass, decreased nighttime pH, and differences in sulfate mass. Moreover, the treatment of detailed aqueous phase chemistry enables the investigation of the formation of aqueous secondary organic aerosol mass. The consideration of size-resolved aqueous phase chemistry shows only slight effects on the chemical model output. Finally, the enhanced model was applied for case studies connected to the field experiment HCCT-2010. For the first time, an aqueous phase mechanism with the complexity of C3.0RED was applied in 3‑D chemistry transport simulations. Interesting spatial effects of real clouds on e.g., tropospheric oxidants and inorganic mass have been studied. The comparison of the model output with available measurements revealed many agreements and also interesting disagreements, which need further investigations

Etude des microemulsions qui sont des solutions transparentes constituees de fines gouttelettes d'eau dispersees dans une phase continue riche en huile. Determination par declin de fluorescence, diffusion de lumiere et conductivite electrique de l'influence de la nature de l'huile, de la temperature et de la structure du tensioactif sur la taille des gouttelettes et les processus d'echange de matiere entre gouttelettes

碩士
國立中山大學
化學系研究所
103
“Aerosols” are broadly referred to ultrafine particulate matters suspended in a gas. These ultrafine suspensions may exist in the form of solid paprticles or liquid droplets with the size ranging from sub-nm up to a few microns. Since aerosols have a great variety in size, shape, composition and architecture, their fundamental physical, chemical and optical properties often deviate considerably from their gaseous and bulk counterparts. To fully understand the underlying origins responsible for their importance in environmental sciences, atmospheric chemistry and planetary sciences, it is crucial to understand the fundamental structural properties of aerosols from the atomic and molecular level. Of particular significance is the valence electronic energetic structure of aerosols, as this property directly governs the chemical activities of aerosols when they undergo chemical reactions with other substances. To address this issue, we have newly constructed an Aerosol VUV Photoelectron Spectroscopy apparatus to probe the valence electron energy structure of aerosols. Aerosols of interest are generated by an atomizer and introduced into the aerosol VUV photoelectron spectroscopy chamber via a set of adjustable aerodynamics lens from which aerosols form a highly collimated aerosol beam. The size distribution and number density of aerosols are pre-characterized by the Scanning Mobility Particle Sizer (SMPS). In this thesis, we first investigated the VUV photoelectron spectra of pure water aerosols utilizing this new VUV aerosol photoelectron spectroscopy. With the superior spectral resolution of the newly constructed aerosol apparatus, the vibrationally resolved fine structure of condensed water is resolved for the first time. Considering that the valence electronic structures of amino acid molecules under the aqueous environments of varying pH values are largely unknown, we interrogated the VUV photoelectron spectra of glycine aqueous aerosols and the thiol (-SH)-containing cysteine aqueous aerosols of varying pH conditions. Under various pH conditions, the solvated amino acid molecules undergo protonation/ deprotonation processes and the amino acid molecule dominate in different form of anion, cation and zwitterion. By probing the evolution of the valence electronic structure of aqueous amino acid aerosols as a function of pH value, this work provides the microscopic insight to illustrate the conventionally macroscopic concept of nucleophilicity and its potential impact in the charge transfer process of many important biological reactions.

Atmospheric aerosols are a major contributor to the total energy balance of the Earth's atmosphere. The exact effect of these aerosols on global climate is not well understood, due to poorly-characterized compositional variation that takes place over a given aerosol's lifetime. Organic aerosol (OA) species are of particular interest, forming through a myriad of gas- and aerosol-phase mechanisms and contributing to aerosol light absorbance, cloud formation properties, and overall particle lifetime. As different organic species will affect physical properties in different ways, proper prediction of these compounds forming in the aerosol phase is necessary to estimate the net physical properties of aerosols, and subsequently their effects on overall global climate. Several previous models exist that attempt to predict organic components of aqueous-phase mass in aerosols, with varying degrees of scope of chemistry and range of applicability. Many of such simulations emphasize OA formation via oxidation of gas-phase organic species that results in low-volatility compounds that subsequently partition into aerosols. Other models focus on aqueous-phase processing of semi-volatile and non-volatile water-soluble organic compounds (WSOC's) under cloud water conditions. However, aqueous reactions that occur in atmospheric, deliquesced salt aerosols have recently also been found to be potentially important additional pathway for the creation of additional aerosol-phase organic mass, contributing different products due to the significantly higher inorganic concentrations present under these conditions. It is desirable to incorporate these reactions into analogous predictive simulations, allowing for the chemistry taking place in small, deliquesced salt atmospheric aerosols to be more accurately represented. In this work, we discuss a new photochemical box model known as GAMMA, the Gas-Aerosol Model for Mechanism Analysis. GAMMA couples gas-phase organic chemistry with highly detailed aqueous-phase chemistry, yielding speciated predictions for dozens of secondary organic aqueous aerosol-phase compounds under various atmospheric and laboratory initial conditions. From these studies, we find that isoprene-derived epoxides (IEPOX) and their substitution products are predicted to dominate aqueous-phase organic aerosol mass in conditions with low NOx in the atmosphere, representative of rural environments. The contribution of these epoxide species is expected to be high under acidic conditions, though our findings still estimate significant contribution to aqueous-phase organic mass under higher pH or under cloudwater conditions, when acidity is expected to be lower. Under high-NOx conditions typical of urban environments, glyoxal is seen to form the majority of evolved aqueous organic species, with organic acids comprising the bulk of the difference. We then implement a series of physical property modules, designed to predict changes in aerosol absorbance and surface tension due to bulk concentrations of evolved OA species. Preliminary results from these modules indicate that bulk solution effects of aqueous-phase carbonyl-containing volatile organic compounds (CVOCs) and organic acids are insufficient to significantly affect net aerosol surface tension under any condition tested, implying that observed deviations from pure inorganic aerosol surface tension will arise from surface-aerosol partitioning rather than bulk compositional effects. Light absorption of aqueous aerosols is seen to be driven by dark glyoxal chemistry in deliquesced salt aerosols and organic acids in cloud droplets, though additional information about the absorbance properties of IEPOX and its derivatives is required to accurately predict the net absorbance of aerosols where these species dominate OA mass. The predictions as described by GAMMA are comparable to field observations, and give further credence to the significance of epoxide formation as a source of aqueous-phase organic aerosol mass. These results also suggest the relative importance of specific organic compounds in the aqueous phase of both deliquesced salt aerosols and cloud droplets in the atmosphere, which gives direction to the study of compounds whose impact on aerosol physical properties will matter the most. In turn, new kinetic and physical information can be directly applied into the groundwork laid here, allowing GAMMA to provide a continuously better understanding of the effect of organic material on aqueous aerosols and their implicit effect on the environment.

Aerosols are known to have a large, uncertain effect on air quality and climate. Chemical processing of organic material in aqueous aerosols is known to form secondary organic aerosols (SOA), which make up a significant portion of particulate mass in the atmosphere. However, lack of clarity surrounding the importance of each source of SOA to total aerosol mass contributes to the uncertainties in their environmental impact. Disagreements between chemical models and field measurements suggest that some processes are misrepresented or are missing in current models. This work considers three pathways of SOA formation using Gas-Aerosol Model for Mechanism Analysis (GAMMA), a photochemical box model developed by the McNeill group featuring coupled gas phase and detailed aqueous phase aerosol chemistry. Imidazole-2-carboxaldehyde (IC), a light-absorbing organic species, has been observed to contribute to SOA formation as a photosensitizer. Currently, the extent of photosensitized reactions in ambient aerosols remains poorly constrained. Reactive uptake coefficients were determined from experimental studies of IC-containing aerosols and scaled for ambient simulations in GAMMA. Results of remote ambient simulations show that IC is unlikely to be a significant source of SOA largely due to its lack of abundance in atmospheric aerosols. Humic-like substances (HULIS) have also been experimentally shown to catalyze SOA formation through photosensitizer chemistry. We use GAMMA to quantify the uptake kinetics of limonene in these photosensitizer experiments. Ambient GAMMA simulations of this SOA formation pathway show that limonene-HULIS photosensitizer chemistry can contribute up to 65% of total aqueous SOA at pH 4. Further laboratory studies are recommended for this SOA source to assess the need for its inclusion in aerosol models. Chemical processing of organic material in cloudwater is another known source of SOA. We use GAMMA to consider the impact of the coupled effect of processing in both aqueous aerosol and cloudwater on isoprene epoxydiol (IEPOX) SOA. Simulations show that cloudwater at pH 3 – 4 can also be a potentially significant source of IEPOX SOA, largely due to higher water content in cloudwater than in aerosols. Thus, cloud processing may be a significant contributor to IEPOX SOA formation and could account for differences between predicted SOA mass and ambient measurements where mass transfer limitations in aerosol particles can be expected. This work concludes with recommendations for future work in GAMMA. Parameterization of glyoxal reactive uptake could allow for more accurate predictions of glyoxal oxidation product distributions. The inclusion of online thermodynamic calculations of inorganic species in GAMMA can better constrain several multiphase chemical processes, such as the highly pH-dependent uptake of IEPOX and sulfate formation. Updated detailed mechanisms of transition metal ion chemistry would also improve predictions of sulfate formation.

氣溶膠是懸浮在空氣中的微粒。它們對人類健康，能見度以及全球氣候均能造成重大影響。當暴露於大氣的氣體氧化劑（例如羥基和臭氧），氣溶膠會在表面附近發生多相氧化並改變化學成分和顆粒大小。有機化合物是氣溶膠的其中一個重要分類，當中不同個體的特性（例如揮發性、氧合程度和極性）各異。有機化合物會視乎其擁有功能群的數量、性質和位置有不同的化學改變。為深入了解分子結構對有機化合物與羥基的多相氧化過程的影響，本論文通過兩組相互關聯的實驗以研究兩個常見的功能群（甲基和羥基）如何影響有機化合物的氧化過程和最終反應產物分布。多相氧化實驗在氣霧流管反應器中進行，並使用裝有可在環境氣壓下運作的電離源（DART）的高分辨率質譜儀來獲得氧化氣溶膠的分子成分信息。論文第一部分比較了二甲基乙酸的兩種異構體（2,2-二甲基乙酸和2,3-二甲基乙酸）的氧化過程，以了解兩個支甲基在不同相對位置對多相氧化的速度和化學的影響。實驗結果顯示2,3-二甲基乙酸的氧化速度是2,2-二甲基乙酸的兩倍。這是由於在2,3-二甲基乙酸的初始氧化過程中，羥基的奪氧反應會形成比較穩定的叔烷基。此外，在兩種異構體的實驗中皆觀測到的醇官能化產物有可能是因位阻效應令烷氧基從分子間奪氧而形成，而碎片化產物則源於烷氧基的分解。結果指出烷氧基化學對於這兩個擁有甲基的二羧酸之化學過程的重要性。論文第二部分研究酒石酸的氧化過程以探討羥基如何影響多相過程。氧化過程產生四種產物：一個C4官能化產物(C4H4O6)和三個碎裂化產物(C3H4O4, C3H2O4, and C3H2O5)。其中的C4官能化產物並不是由過氧自由基自反應中產生，而是從α-羥基過氧自由基的單分子超氧化氫消除過程中形成。官能化和碎裂化產物均佔總質量的重要部分。雖然充氧的有機氣溶膠通常有利碎裂化過程，但此觀察顯示官能化過程對於這種高度氧化的有機酸是重要的。兩組實驗的結果清楚展示出有機化合物的分子結構很有程度控制氧化動力學和氧化中的化學作用，故有需要知道有機分子中的功能群的性質和位置以了解功能化和碎裂化的化學過程之間的競爭。
Aerosols are suspending particulates in air that can greatly affect human health, visibility as well as the global climate. When exposed to gas phase oxidants (e.g. hydroxyl (OH) radical and ozone), atmospheric aerosols undergo oxidation at or near the aerosol surface that can significantly modify the aerosol size, composition, and properties (termed heterogeneous oxidation). Organic compounds contribute a significant fraction of the total aerosol mass and have a wide range of properties such as volatility, degree of oxygenation, and polarity. Depending on the number, types and positions of the functional groups, organic compounds can chemically evolve via very different mechanisms. To better understand how the molecular structure governs the heterogeneous OH chemistry of organic aerosols, we investigate the role of two functional groups (methyl and hydroxyl groups), which are commonly present in atmospheric organic compounds, in governing the oxidative kinetics and reaction mechanisms of small oxygenated organic compounds. Heterogeneous OH oxidation experiments are carried out using an atmospheric pressure aerosol flow tube reactor and the molecular composition of the aerosols before and after oxidation are obtained by a high resolution mass spectrometer coupled with an atmospheric pressure soft ionization source (referred to as Direct Analysis in Real Time, DART).
In the first study, the OH oxidation of two structural isomers of dimethylsuccinic acid (2,2-dimethylsuccinic acid (2,2-DMSA) and 2,3dimethylsuccinic acid (2,3-DMSA)) is investigated to examine the effect of the relative locations of two branched methyl groups on the heterogeneous oxidative kinetics and chemistry. The heterogeneous reaction of OH radicals with 2,3-DMSA is about 2 times faster than that of 2,2-DMSA. This can be explained by the formation of stable tertiary alkyl radicals by the initial hydrogen abstraction of 2,3-DMSA. For the two isomers, the formation of alcohol functionalization products is likely attributed to the intermolecular hydrogen abstraction of alkoxy radicals due to the steric effect of the two methyl groups, while the fragmentation products are originated from the decomposition of alkoxy radicals. These results suggest that the alkoxy radical chemistry plays an important role in the heterogeneous chemistry of these two methyl substituted dicarboxylic acid.
In the second study, we investigate the OH radical-initiated oxidation of tartaric acid to examine how the presence of hydroxyl groups controls the heterogeneous reaction mechanisms. Four major reaction products are formed: a single C4 functionalization product (C4H4O6) and three C3 fragmentation products (C3H4O4, C3H2O4, and C3H2O5). The C4 functionalization product does not appear to originate from peroxy radical self-reactions, but likely forms via the unimolecular HO2 elimination from an α-hydroxylperoxy intermediate, enhanced by the proximity of a hydroxyl group. Both functionalization and fragmentation products contribute significantly to the total aerosol mass. Generally, fragmentation processes are expected to be more favorable than functionalization processes when organic aerosols become more oxygenated, but our observations suggest that functionalization processes can be the dominant reaction pathways for this highly oxygenated organic acid.
Overall, the results have clearly demonstrated that the molecular structure of an organic molecule largely controls the heterogeneous oxidative kinetics and reaction mechanisms. Knowledge on the nature and positions of the functional groups is important to understand the competition between functionalization and fragmentation processes during the oxidation.
Cheng, Chiu Tung.
Thesis M.Phil. Chinese University of Hong Kong 2016.
Includes bibliographical references (leaves ).
Abstracts also in Chinese.
Title from PDF title page (viewed on …).
Detailed summary in vernacular field only.

abstract: Atmospheric particulate matter (PM) has a pronounced effect on our climate, and exposure to PM causes negative health outcomes and elevated mortality rates in urban populations. Reactions that occur in fog can form new secondary organic aerosol material from gas-phase species or primary organic aerosols. It is important to understand these reactions, as well as how organic material is scavenged and deposited, so that climate and health effects can be fully assessed. Stable carbon isotopes have been used widely in studying gas- and particle-phase atmospheric chemistry. However, the processing of organic matter by fog has not yet been studied, even though stable isotopes can be used to track all aspects of atmospheric processing, from particle formation, particle scavenging, reactions that form secondary organic aerosol material, and particle deposition. Here, carbon isotope analysis is used for the first time to assess the processing of carbonaceous particles by fog. This work first compares carbon isotope measurements (δ13C) of particulate matter and fog from locations across the globe to assess how different primary aerosol sources are reflected in the atmosphere. Three field campaigns are then discussed that highlight different aspects of PM formation, composition, and processing. In Tempe, AZ, seasonal and size-dependent differences in the δ13C of total carbon and n-alkanes in PM were studied. δ13C was influenced by seasonal trends, including inversion, transport, population density, and photochemical activity. Variations in δ13C among particle size fractions were caused by sources that generate particles in different size modes. An analysis of PM from urban and suburban sites in northeastern France shows how both fog and rain can cause measurable changes in the δ13C of PM. The δ13C of PM was consistent over time when no weather events occurred, but particles were isotopically depleted by up to 1.1‰ in the presence of fog due to preferential scavenging of larger isotopically enriched particles. Finally, the δ13C of the dissolved organic carbon in fog collected on the coast of Southern California is discussed. Here, temporal depletion of the δ13C of fog by up to 1.2‰ demonstrates its use in observing the scavenging and deposition of organic PM.
Dissertation/Thesis
Doctoral Dissertation Chemistry 2018

碩士
國立中山大學
化學系研究所
104
“Aerosols” are broadly referred to ultrafine particulate suspension. The crucial roles of aerosols have been increasingly recognized in a variety of important research fields, including the atmospheric chemistry, environment chemistry and interstellar chemistry. Its implications in the biological and biomedical sciences have also been actively explored. In order to obtain the valence electronic structural information of aerosols, a novel VUV photoelectron spectroscopy apparatus has been recently built, using the VUV synchrotron-based radiation as the ionization source. In this thesis, the valence electronic structures of several species that are of particular significance in the biological science and in the environmental chemistry have been systematically investigated, including the biologically important glutamic acid (Glu), glutathione (GSH) tripeptide, and the environmentally important inorganic aerosols. Glutamic acid is one of the precursors of GSH, and in the mean while, a crucial amino acid governing the neural activation and brain functionality. The valence electronic structure of Glu at varying pH conditions are investigated for the first time in the aqueous aerosol phase and are presented in Chapter 3. On the other hand, glutathione (L-γ-glutamyl-cysteinyl-glycine, GSH) is one of the most powerful antioxidant in nature. By preferentially reacting with various endogenous and exogenous oxidants, it readily scavenges harmful free radicals and reactive species, thereby preventing functional proteins and enzymes in tissue cells from oxidative damages. Despite its remarkable biological significance, however, the electronic structure of GSH remains unavailable. To gain insights into the intrinsic origin underlying its superior antioxidant capacity, the valence electronic structure of GSH have been studied for the first time in the aqueous aerosol form and presented in Chapter 4. The VUV photoelectron spectra of GSH and its constituting amino acids are obtained at several representative pH conditions, reflecting the changing molecular characters of the dominating chemical species. Upon systematic spectroscopic analysis, the profound molecular origin responsible for the powerful antioxidant ability of this super antioxidant is revealed. Though the thiol functional group of GSH is the key player involved in most redox reactions it undergoes, the functional roles of the other two composite amino acids of GSH, Glu and Gly in making GSH a superior antioxidant are discussed. In addition to the implication in the biological chemistry, the implication of aerosols in the environment science has also been addessed in this thesis, as presented in Chapter 5. PM2.5 particles, which are referred to particulate matters with an aerodynamic diameter smaller than 2.5 micrometers, are known to cause respiratory and cardiovascular diseases. The main chemical compositions of PM2.5 pollutions include sulfates, nitrates, hydrocarbons, carbon monoxide and heavy metals. They are considered as optical active and high oxidizing species. These hazardous aerosols in the environment, such as sulfate, nitrate, and ammonium may undergo photochemical reactions to form radicals and influence living organisms. In Chapter 5, the valence electronic structure of several critical inorganic salts in environment, including nitrate and sulfate are investigated. By doing so, we attempt to better understand the possible impacts of the inorganic aerosols towards the environment as well as the homeostasis of human health.

The aqueous phase photo-oxidation of water soluble organic compounds (WSOC) extracted from α-pinene ozonolysis secondary organic aerosol (SOA) was investigated using high resolution time-of-flight chemical ionization mass spectrometry (CI-ToFMS). The results have shown that WSOC get more functionalized and fragmented as the reaction proceeds. The capabilities of three reagent ions, were assessed; specifically, (H2O)nH+ ionizes organic compounds with carbon oxidation state (OSC) ≤ 1.3, whereas CH3C(O)O- and I(H2O)n- ionize highly oxygenated organics with OSC up to 4, with I(H2O)n- showing more selectivity. The aqueous phase OH oxidation of cis-pinonic acid and tricarballylic acid (a surrogate for 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), recognized as a tracer of α-pinene SOA) were also studied. The respective rate constants at 301 K were measured to be 3.4(±0.5)×10^9 M^-1s^-1 at pH=2 and 3.1(±0.3)×10^8 M^-1s^-1 at pH=4.6. This work also illustrates possible aqueous phase mechanism for MBTCA formation from cis-pinonic oxidation.

Atmospheric aerosol chemistry is important in areas ranging from urban air pollution to cloud formation. It has long been supposed that droplet-phase reactions account for a significant fraction of the atmospheric conversion of SO₂ to sulfate. Among such reactions is the manganese-catalyzed aqueous-phase oxidation of SO₂. Whereas the role of aqueous phase SO₂ oxidation in the dilute solutions characteristic of fog and cloud droplets (diameter > 10 µm) has been reasonably well established, the role of comparable reaction in submicron aerosols is uncertain. In this thesis a reactor system is developed to carry out gas-aerosol reactions under humid, ambient-like conditions. The apparatus consists of a continuous stirred tank reactor (CSTR) in which the growth of the aqueous aerosol is measured. Absence of mass transfer limitation, coagulation, and nucleation ensure that particle growth is direct evidence of reaction. Special care is taken to minimize size biasing of the aqueous aerosol in the electrostatic classifier used to measure the reactor feed and effluent distributions. Aerosol behavior in the reactor is modeled assuming an ideal CSTR and, given the solution thermodynamics and equilibrium chemistry, the effluent distribution can be predicted using one of the proposed reaction rate mechanisms.

Experiments were performed using a pure MnSO₄ or a MnSO₄-Na₂SO₄ mixture feed aerosol. The relative humidity ranged from 86 to 94% and 0.1 ppm < p_SO₂, < 50 ppm. The slow, approximately constant reaction rate of Bronikowski and Pasiuk-Bronikowska (1981) (R ~ 2 x 10⁻⁴ Ms⁻¹) was found to best predict the observed growth over the entire range of operating conditions. The various rate expressions proposed for this system in the literature resulted in varying estimates of growth. When reactor conditions were similar to those at which the rate expression was determined, the agreement between the predicted and observed distributions improved. This indicates that use of a rate expression beyond its specified range may result in erroneous predictions.

碩士
國立中山大學
化學系研究所
106
Aerosol are broadly defined as particulate matters suspended in the air. They may exist either as solids or liquid droplets, with sizes ranging from a few nanometers up to hundreds of micrometers. The physical, chemical, optical and biological properties of aerosols may be inherently governed by their chemical compositions, external morphology and internal structures. Aerosols play important roles in the field of environmental chemistry, atmospheric chemistry and biological chemistry. The primary goal of this thesis is to investigate the intrinsic valence electronic properties of nanoscaled aerosols. Three major types of aerosols have been chosen for study in this thesis, including: I) pure water nanoaerosols, II) three basic amino acids and III) amphiphilic phenolic-containing aqueous aerosols. The aerosol VUV photoelectron spectroscopy has been applied as the major experimental investigation tool, and the synchrotron radiation generated VUV has been used as the photoionization source. To gain a better understanding on the nature of water nanoaerosols, I have first applied the kinetic theory of evaporation to estimate the size and temperature of pure water nanoaerosols at the photoionization region by taking the evaporative cooling effect into consideration. The VUV photoelectron spectra of pure H2O and D2O aerosols have been measured and compared, from which the nature and possible microscopic structures of water aerosols are interrogated. In the second part of this thesis, I studied the solvated electronic structures of three basic amino acids, including Lysine, Arginine and Histidine in the form of aqueous aerosols. These three basic amino acids are often involved in the hydrogen bond formation by acting as the hydrogen bond donor. By measuring the pH-dependent valence photoelectron spectra of these three basic amino acids, their vertical ionization energies in association with protonation/deprotonation status and the possible role of the side chain in affecting the valence electronic properties are interrogated. 　　The interfacial properties and surface pH of aqueous aerosols play determinant roles in affecting their chemical activities. In the third part of this thesis, I investigated the surface pH of nanoscaled aqueous aerosols. Due to the amphiphilic nature of phenol, it is only partially solvated and thus favorably provide a surface-sensitive probe to assess the surface pH of aqueous interface. In this thesis, I investigate the surface pH of phenol aqueous aerosols at several chosen pH conditions, with a goal to examine whether the surface-to-bulk pH difference varies with pH conditions. From the investigations on the three specific types of aqueous nanoaerosols, new insights regarding the valence electronic properties, interfacial solvation structures and corresponding energetic properties can be gained.

Die chemische Zusammensetzung und die physikalischen Eigenschaften von troposphärischen Gasen, Partikeln und Wolken hängen aufgrund zahlreicher Prozesse stark voneinander ab. Insbesondere chemische Multiphasenprozesse in Wolken können die physiko-chemischen Eigenschaften der Luft und troposphärischer Partikel klein- und großräumig verändern. Diese chemische Prozessierung des troposphärischen Aerosols innerhalb von Wolken beeinflusst die chemischen Umwandlungen in der Atmosphäre, die Bildung von Wolken, deren Ausdehnung und Lebensdauer, sowie die Transmissivität von einfallender und ausgehender Strahlung durch die Atmosphäre. Damit sind wolken-chemische Prozesse relevant für das Klima auf der Erde und für verschiedene Umweltaspekte. Daher ist ein umfassendes Verständnis dieser Prozesse wichtig. Die explizite Behandlung chemischer Reaktionen in der Flüssigphase stellt allerdings eine Herausforderung für atmosphärische Computermodelle dar. Detaillierte Beschreibungen der Flüssigphasenchemie werden deshalb häufig nur für Boxmodelle verwendet. Regionale Chemie-Transport-Modelle und Klimamodelle berücksichtigen diese Prozesse meist nur mit vereinfachten chemischen Mechanismen oder Parametrisierungen. Die vorliegende Arbeit hat zum Ziel, den Einfluss der chemischer Mehrphasenprozesse innerhalb von Wolken auf den Verbleib relevanter Spurengase und Partikelbestandteile mit Hilfe des state‑of‑the‑art 3D-Chemie-Transport-Modells COSMO-MUSCAT zu untersuchen. Zu diesem Zweck wurde das Model um eine detaillierte Beschreibung chemischer Prozesse in der Flüssigphase erweitert. Zusätzlich wurde das bestehende Depositionsschema verbessert, um auch die Deposition von Nebeltropfen zu berücksichtigen. Die durchgeführten Modellerweiterungen ermöglichen eine bessere Beschreibung des troposphärischen Multiphasensystems. Das erweiterte Modellsystem wurde sowohl für künstliche 2D-Bergüberströmungsszenarien als auch für reale 3D-Simulationen angewendet. Mittels Prozess- und Sensitivitätsstudien wurde der Einfluss (i) des Detailgrades der verwendeten Mechanismen zur Beschreibung der Flüssigphasenchemie, (ii) der Größenauflösung des Tropfenspektrums und (iii) der Tropfenanzahl auf die chemischen Modellergebnisse untersucht. Die Studien belegen, dass die Auswirkungen der Wolkenchemie aufgrund ihres signifikanten Einflusses auf die Oxidationskapazität in der Gas- und Flüssigphase, die Bildung von organischer und anorganischer Partikelmasse sowie die Azidität der Wolkentropfen und Partikel in regionalen Chemie-Transport-Modellen berücksichtigt werden sollten. Im Vergleich zu einer vereinfachten Beschreibung der Wolkenchemie führt die Verwendung des detaillierten chemischen Flüssigphasenmechanismus C3.0RED zu verringerten Konzentrationen wichtiger Oxidantien in der Gasphase, einer höheren Nitratmasse in der Nacht, geringeren nächtlichen pH-Werten und einer veränderten Sulfatbildung. Darüber hinaus ermöglicht eine detaillierte Wolkenchemie erst Untersuchungen zur Bildung sekundärer organischer Partikelmasse in der Flüssigphase. Die größenaufgelöste Behandlung der Flüssigphasenchemie hatte nur geringen Einfluss auf die chemischen Modellergebnisse. Schließlich wurde das erweiterte Modell für Fallstudien zur Feldmesskampagne HCCT‑2010 genutzt. Zum ersten Mal wurde dabei ein chemischer Mechanismus mit der Komplexität von C3.0RED verwendet. Die räumlichen Effekte realer Wolken z. B. auf troposphärische Oxidantien oder die Bildung anorganischer Masse wurden untersucht. Der Vergleich der Modellergebnisse mit verfügbaren Messungen hat viele Übereinstimmungen aber auch interessante Unterschiede aufgezeigt, die weiter untersucht werden müssen.
In the troposphere, a vast number of interactions between gases, particles, and clouds affect their physico-chemical properties, which, therefore, highly depend on each other. Particularly, multiphase chemical processes within clouds can alter the physico-chemical properties of the gas and the particle phase from the local to the global scale. This cloud processing of the tropospheric aerosol may, therefore, affect chemical conversions in the atmosphere, the formation, extent, and lifetime of clouds, as well as the interaction of particles and clouds with incoming and outgoing radiation. Considering the relevance of these processes for Earth\''s climate and many environmental issues, a detailed understanding of the chemical processes within clouds is important. However, the treatment of aqueous phase chemical reactions in numerical models in a comprehensive and explicit manner is challenging. Therefore, detailed descriptions of aqueous chemistry are only available in box models, whereas regional chemistry transport and climate models usually treat cloud chemical processes by means of rather simplified chemical mechanisms or parameterizations. The present work aims at characterizing the influence of chemical cloud processing of the tropospheric aerosol on the fate of relevant gaseous and particulate aerosol constituents using the state-of-the-art 3‑D chemistry transport model (CTM) COSMO‑MUSCAT. For this purpose, the model was enhanced by a detailed description of aqueous phase chemical processes. In addition, the deposition schemes were improved in order to account for the deposition of cloud droplets of ground layer clouds and fogs. The conducted model enhancements provide a better insight in the tropospheric multiphase system. The extended model system was applied for an artificial mountain streaming scenario as well as for real 3‑D case studies. Process and sensitivity studies were conducted investigating the influence of (i) the detail of the used aqueous phase chemical representation, (ii) the size-resolution of the cloud droplets, and (iii) the total droplet number on the chemical model output. The studies indicated the requirement to consider chemical cloud effects in regional CTMs because of their key impacts on e.g., oxidation capacity in the gas and aqueous phase, formation of organic and inorganic particulate mass, and droplet acidity. In comparison to rather simplified aqueous phase chemical mechanisms focusing on sulfate formation, the use of the detailed aqueous phase chemistry mechanism C3.0RED leads to decreased gas phase oxidant concentrations, increased nighttime nitrate mass, decreased nighttime pH, and differences in sulfate mass. Moreover, the treatment of detailed aqueous phase chemistry enables the investigation of the formation of aqueous secondary organic aerosol mass. The consideration of size-resolved aqueous phase chemistry shows only slight effects on the chemical model output. Finally, the enhanced model was applied for case studies connected to the field experiment HCCT-2010. For the first time, an aqueous phase mechanism with the complexity of C3.0RED was applied in 3‑D chemistry transport simulations. Interesting spatial effects of real clouds on e.g., tropospheric oxidants and inorganic mass have been studied. The comparison of the model output with available measurements revealed many agreements and also interesting disagreements, which need further investigations.

The first step of this work was the construction of the flow reactor which used to generate SOA by the gas-phase ozonolysis of limonene (limSOA). The generation of limSOA was performed under precisely controlled conditions (RH, temperature, pressure as well as concentrations of the ozone and the precursor). Precursor concentration of limonene inside the flow reactor was monitored off-line with GC/FID. In the flow reactor, it was possible to generate 20 limonene oxidation products since a separate synthesis and purification of each of these compounds would be very complicated and time-consuming. Afterward, the limSOA produced in the flow reactor were extracted into a buffered water solution and oxidized by OH and O3 under different pH conditions. Since the atmosphere contains a large amount of liquid water, this work allows to provide detailed insights into the kinetics of limSOA aging in clouds, fogs, and wet aerosols. LimSOA oxidation by OH and O3 were investigated using LC-ESI/MS/MS. The second step of this work was the investigation of kinetics, mechanisms and the yield of the products resulting from the ozonolysis of LA and BCA in the aqueous phase. Initially, LA and BCA were synthesized and purified by semi-preparative liquid chromatography since these acids are not commercially available. Obtained results indicate that kozone for the reaction of ozone with BCA was higher than those for the reaction of ozone with LA under both acidic and basic conditions most likely due to the cyclobutyl ring strain in the BCA molecule. Subsequently, the molar yields of BCA and LA ozonolysis products were quantified. LC/MS as well as UV-Vis spectroscopy for analyzing formaldehyde and hydroperoxides were used. The data acquired with LC coupled to the ultrahigh-resolution MS indicated that the terminal C=C bond in LA and BCA was converted into C=O moiety forming a keto-LA and keto-BCA as products. As inferred from the data acquired, products of LA and BCA have similar molar yields which indicated that these acids react with ozone in a similar way. It was proposed that H2O2 and formaldehyde are formed by the decomposition of stabilized Criegee intermediate (SCI) as a result of its reaction with water. Moreover, the molar yields of peroxides, formaldehyde, and keto-acids, along with the experimental data acquired are strongly indicated that the branching ratios of the primary ozonides (POZs) or both acids (LA and BCA) were nearly identical. The third step was the investigation of kinetics and mechanism of the aqueous-phase oxidation of BCA by hydroxyl radicals. The obtained results indicate that kOH of BCA exceeds the diffusion limit for the aqueous-phase oxidation of organic compounds by OH. Since OH reacts unselectively with organic compounds, a number of products were identified by ultrahigh-resolution MS resulting from OH reaction with BCA. Three generation of products were found. First-generation products that were identified are keto-BCA and hydroxyl-hydroperoxy BCA. These two molecules were following OH addition to the terminal C=C bond of the precursor. The rest of the products were identified as second and third-generation products which are oxygenated BCA derivatives with O:C ratios higher than the precursor although some fragmentation of the original carbon backbone was also observed. The first-generation products are mainly generated via the decomposition of tetroxides forming for pathways which in turn produced the first-generation products. The second-generation products are produced by the cyclobutene ring-opening or via the further oxidation of the first-generation products. The third-generation product was identified as highly oxidized products with two carboxylic moieties resulting from the conversion of second-generation product. Thus, the data acquired provided detailed insights into the mechanism of BCA + OH reaction.
Pierwszym krokiem w pracy była budowa reaktora przepływowego, który służył do wytwarzania SOA poprzez ozonolizę w fazie gazowej limonenu (limSOA aerozol limonenowy). Generowanie limSOA przeprowadzono w ściśle kontrolowanych warunkach (wilgotność względna, temperatura, ciśnienie, a także stężenia ozonu i prekursora). Stężenie limonenu w reaktorze przepływowym monitorowano w trybie off-line za pomocą GC / FID. W reaktorze przepływowym można było wytworzyć 20 produktów utleniania limonenu, ponieważ oddzielna synteza i oczyszczanie każdego z tych związków byłoby bardzo skomplikowane i czasochłonne. Następnie limSOA wytworzony w reaktorze przepływowym ekstrahowano do buforowanego roztworu wodnego i utleniano z użyciem OH oraz O3 w różnych pH. Ponieważ atmosfera zawiera dużą ilość wody w stanie ciekłym, praca ta pozwala na uzyskanie szczegółowych informacji na temat kinetyki starzenia limSOA w chmurach, mgle i mokrych aerozolach. Utlenianie limSOA przez OH oraz O3 badano z pomocą chromatografii cieczowej sprzężonej ze tandemową spektrometrią mas (LC-ESI/MS/MS). Drugim etapem pracy było zbadanie kinetyki, oraz mechanizmów i wydajności produktów reakcji powstałych w wyniku ozonolizy kwasu limonenowego (LA) oraz kwasu kariofilenowego (BCA) w fazie wodnej. LA i BCA zsyntetyzowano i oczyszczono metodą półpreparatywnej chromatografii cieczowej, ponieważ kwasy te nie są dostępne w handlu. Uzyskane wyniki wskazują, że stałe szybkości reakcji ozonu z BCA były wyższe niż stałe szybkości reakcji ozonu z LA zarówno w warunkach kwaśnych, jak i zasadowych. Wiąże się to najprawdopodobniej istnienie pierścienia cyklobutylowego w cząsteczce BCA. Następnie określono ilościowo wydajności molowe produktów ozonolizy BCA i LA. Do analizy formaldehydu i wodoronadtlenków wykorzystano LC-ESI/MS/MS oraz spektrometrię UV-Vis. Dane uzyskane za pomocą LC sprzężonego z MS o wysokiej rozdzielczości masowej wskazywały, że końcowe wiązanie C = C w LA i BCA zostało przekształcone w ugrupowanie C = O, tworząc keto-LA i keto-BCA jako produkty. Jak wynika z uzyskanych danych, produkty LA i BCA mają podobne wydajności molowe, co wskazuje, że kwasy te reagują w podobny sposób z ozonem. Zaproponowano, że H2O2 i formaldehyd powstają w wyniku rozkładu stabilizowanego półproduktu Criegee (SCI) w skutek jego reakcji z wodą. Co więcej, wydajności molowe nadtlenków, formaldehydu i ketokwasów, wraz z uzyskanymi danymi eksperymentalnymi, wyraźnie wskazują, że stosunki rozgałęzień pierwotnych ozonidów (POZ) lub obu kwasów (LA i BCA) były prawie identyczne. Trzecim krokiem było zbadanie kinetyki i mechanizmu utleniania BCA w fazie wodnej przez rodniki hydroksylowe. Uzyskane wyniki wskazują, że kOH dla BCA przekracza granicę dyfuzji dla utleniania związków organicznych w fazie wodnej przez OH. Ponieważ OH reaguje nieselektywnie ze związkami organicznymi, wiele produktów reakcji z OH z BCA musiało zostać zidentyfikowanych z pomocą MS o wysokiej rozdzielczości, Znaleziono produkty trzech generacji. Zidentyfikowane produkty pierwszej generacji to keto-BCA i hydroksylo-hydroperoksy BCA. Te dwie cząsteczki powstawały po przyłączeniu OH do końcowego wiązania C = C prekursora. Pozostałe produkty zidentyfikowano jako produkty drugiej i trzeciej generacji, które są utlenionymi pochodnymi BCA o stosunku O:C wyższym niż w prekursorze, chociaż zaobserwowano również fragmentację pierwotnego szkieletu węglowego. Produkty pierwszej generacji powstają głównie w wyniku rozkładu tetroksydów tworzących ścieżki, które z kolei wytwarzają produkty pierwszej generacji. Produkty drugiej generacji są wytwarzane poprzez otwarcie pierścienia cyklobutenu lub poprzez dalsze utlenianie produktów pierwszej generacji. Produkt trzeciej generacji zidentyfikowano jako produkty silnie utlenione z dwoma resztami karboksylowymi powstałymi w wyniku konwersji produktu drugiej generacji. Tak więc uzyskane dane dostarczyły szczegółowych informacji na temat mechanizmu reakcji BCA + OH.