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Les composés organiques volatils d’origine biogénique (COVB) contribuent à plus de 90% des émissions des COV dans l'atmosphère. Ces composés sont éliminés de l’atmosphère par réaction avec les photo-oxydants (OH, NO3, Cl et O3) et par photolyse. Ces processus sont gouvernés par un mécanisme en chaîne dont les porteurs sont des radicaux libres tels que les radicaux peroxyles RO2 qui jouent un rôle clé dans la dégradation atmosphérique des COV. Dans ce contexte, cette thèse se concentre d’une part sur l’étude cinétique en température et mécanistique de la réaction d’ozonolyse, la détermination des spectres UV et la photolyse de six COV oxygénés insaturés (trans-2-pentènal, trans-2-hexènal, 2-méthyl-2-pentènal, 1-pentèn-3-ol, cis- 2-pentèn-1-ol et trans-3-hexèn-1-ol), et d’autre part l’étude de la réactivité de trois radicaux peroxyles (CH3OCH2O2, CH3C(O)CH2O2 et (CH3)2C(OH)CH2O2) vis-à-vis des radicaux nitrates à différentes températures. Trois dispositifs expérimentaux sont utilisés : une chambre de simulation atmosphérique couplée à une spectroscopie infrarouge à transformée de Fourier (FTIR) et à une chromatographie en phase gazeuse associée à une spectrométrie de masse (GC/MS), un dispositif de mesure des spectres UV-Visible et la photolyse laser couplée à une spectrométrie UV-visible et diode laser. Ces dispositifs associés à des méthodes de traitement permettent d'extraire des données cinétiques en température, mécanistiques et spectroscopiques. Les paramètres cinétiques obtenus sont utilisés pour estimer les durées de vie atmosphériques des espèces étudiées. Les résultats mécanistiques sont utilisés pour élaborer les mécanismes d’ozonolyse de ces composés. Toutes ces données permettent d’enrichir les bases de données cinétiques, mécanistiques et spectroscopiques qui alimentent les modèles atmosphériques. / Biogenic volatile organic compounds (BVOC) account for 90% of VOC emissions in the atmosphere. These VOCs can be removed from the atmosphere by reaction with photo-oxidants (OH, NO3, Cl and O3) as well as by photolysis. All these processes are governed by a chain mechanism whose carriers are mainly free radicals such as peroxy radicals RO2. Hence the importance of characterizing the reactivity of these species that play a key role in the atmospheric degradation of VOCs. In this context, this thesis focuses on the determination of the temperature dependent kinetic data as well as the mechanism of the ozonolysis reaction and the UV absorption spectra along the photolysis of six unsaturated oxygenated VOCs (trans- 2-pentenal, trans-2-hexenal, 2-methyl-2-pentenal, 1-penten-3-ol, cis-2-penten-1-ol and trans-3-hexen-1-ol). Likewise, the temperature dependent kinetic parameters of the reaction of three peroxy radicals (CH3OCH2O2, CH3C(O)CH2O2 et (CH3)2C(OH)CH2O2) with nitrate radicals were also determined. Three experimental setups coupled to treatment methods were used to extract these data: an atmospheric simulation chamber coupled to both a Fourier-transform infrared spectroscopy (FTIR) and a gas chromatography connected to a mass spectrometry (GC/MS), a device for measuring UV-Visible spectra and a laser photolysis coupled with UV-visible spectrometry and laser diode spectroscopy. The kinetic parameters were used to estimate the atmospheric lifetimes of the studied species. While the mechanistic data were used to establish their ozonolysis mechanisms. All the collected data enrich kinetic, mechanistic and spectroscopic databases, improving atmospheric models specially those involving VOCs.

This dissertation is a collection of works that investigate non-prototypical sources leading to new particle formation in the atmosphere. Particles play a major role in atmospheric chemistry. For example, particles are a component of smog and are commonly found in high concentrations under conditions of atmospheric inversions. In order to reconcile the difference between measured and modeled particle concentrations new mechanisms from non-prototypical sources for particle formation need to be determined. Formation of particles has frequently been modeled using classical nucleation theory (CNT). The first step in CNT is the nucleation step where molecular clusters form. In a second step, these clusters grow into particles through coagulation or condensation. First, this research aims to improve the modeling of equilibrium constants for the formation of peroxy radical-water complexes. Failure of the harmonic approximation in the partition function for describing the low frequency vibrational modes of the complexes was explored. Instead the dissociative hydrogen bond mode using a Lennard-Jones 6-3 potential and the other low frequency vibrational modes using one- and two-fold hindered rotors was modeled. It was determined that the contribution of the two-fold hindered rotors is more important than the long-range dipole-dipole potentials and of vibration-rotation coupling. In related work, the hydroperoxy radical was investigated as a non-prototypical source of particles using high level ab initio calculations. The results indicate that the addition of an amine to the dimer increased the overall stability of complex through the increased number and strength of the hydrogen bonds. When compared to prototypical systems, sulfuric acid and methane sulfonic acid, the strength of the complex was found to be similar to the peroxy radical system. Finally, carboxylic acids, formic acid and acetic acid, were investigated as a source for new particle formation using computational and experimental techniques. Using a slow flow reactor cell particle formation was enhanced by the addition of trimethylamine. High level ab initio calculations indicate like the peroxy radicals, carboxylic acids may act as a molecular cluster in particle formation

The Ph.D. thesis was focused on EPR study of redox reactions of selected types of phenols, secondary amines and diperoxy coumpounds. Within the study some redox agents were employed in nonpolar, in some special cases also in polar solvents. EPR spectra of generated radical products were interpreted using spectral simulation. Study of radical reactions under participation of phenols was preferentially concentrated on the behavior of para methyl substituted phenols, where the instability of this substituent in relation to the applied redox agents was evaluated. The tendency towards the abstraction of hydrogen from methyl group, representing the paralell mechanism to the hydrogen abstaction from phenolic OH group was proved. The generated benzyl radicals were undirectly detected in the form of adducts with aromatic nitroso compounds. These adducts undergo the consecutive transformations, leading to the formation of new types of phenoxy radicals. The study of the decomposition of NH bonds was performed with substituted N,N´-paraphenylenediamines, 1-anilino-1-phenylpentane-3-ones and amino substituted 1,3-dimethyluracils. By the oxidation with 3-chloroperbenzoic acid the corresponding nitroxyl radicals were prepared. In the case of 1-anilino-1-phenylpentane-3-ones the aminyl radicals were prepared by the oxidation with PbO2, which existence was evidenced by spin trapping method with nitrosobenzene. In the framework of the investigation of the decomposition of -O-O- bonds the oxygen centred radicals, generated from peroxidic compounds of Luperox type using selected redox agents were detected by spin trapping method. The analysis of EPR spectra documented that primary alkoxyl radicals undergo the consecutive fragmentation, which leads in the presence of oxygen to the formation of secondary alkoxyl radicals. The generation of oxygen centred radicals during the decomposition was indirectly proved in the presence of model phenolic compounds, where due to the abstraction of hydrogen from phenolic OH group the phenoxyl radicals are formed.

En nyligen genomförd studie visade att reaktioner mellan vissa radikaler och omättade alkener är snabbare vid rumstemperatur än vad man tidigare har trott. Dessa reaktioner är viktiga för atmosfäriska oxidationscykler och följaktligen var syftet med detta masterprojekt att beräkna hastighetskonstanterna för dessa reaktioner mellan metyljodid och 1-jodidpentan med tetrametyletylen, isopren och limonen vid rumstemperatur genom att kvantifiera respektive epoxid; tetrametyloxiran, isoprenmonoxid och limonen 1,2 epoxid, som producerades. För att uppfylla syftet utfördes experiment på referensföreningarna tetrametyletylen, isoprenmonoxid, limonen och limonen 1,2 epoxid och på prover tagna från en kolonnflödesreaktor. Dessa experiment genomfördes för att kunna utveckla en lämplig provtagningsmetod och analysmetod med termisk desorptionsenhet samt gaskromatografi och masspektrometri (TD-GCMS). Slutsatsen som drogs var att Tenax® TA adsorbentrör är kompatibla med dessa ämnen och att den föreslagna TD-GCMS metoden är effektiv. Dessutom drogs slutsatsen att tetrametyloxiran inte hittades i reaktorproverna (varken i alkenproverna eller reaktorproverna), vilket resulterade i att hastighetskonstanten inte kunde beräknas. Dessutom var kvantifiering av reaktorproverna inte möjlig. / A recent study has shown that the reaction between some radicals and unsaturated alkenes is faster at room temperature than previously believed. These reactions are important for atmospheric oxidation cycles and therefore the purpose of this master project was to measure the rate coefficients for the reactions between methyl iodine and 1-iodopentane with tetramethylethylene, isoprene and limonene at room temperature by quantifying the respective epoxide; tetramethyloxirane, isoprene monoxide and limonene 1,2 epoxide, produced. In order to fulfill the purpose, experiments were conducted using the reference compounds of tetramethylethylene, isoprene monoxide, limonene and limonene 1,2 epoxide and on column flow reactor samples produced in the above mentioned reactions. These were performed in order to be able to develop an appropriate sampling method, and analysis method using thermal desorption unit gas chromatography and mass spectrometry (TD-GCMS). It was concluded that Tenax® TA adsorbent tubes are compatible with these substances and that the TD-GCMS method suggested is appropriate. It was also concluded that no tetramethyloxirane was found in the reactor samples (neither in alkene samples nor after the reactions), resulting in that it was not possible to calculate the rate coefficient. Moreover, the quantification of the reactor samples was not possible.