Isoprene is the dominant non-methane organic compound emitted by vegetation into the atmosphere, with a global emission rate of ~ 500 Tg yr-1. Its oxidation serves as a major source of ground level ozone in North America during the summer months. Despite the significant impact on tropospheric chemistry, questions remain concerning the detailed oxidation mechanism. The initial step in the mechanism is the addition of OH to form four distinct isomers. The relative branching between these isomers influences the distribution of the final products. I present a comprehensive investigation into the mechanistic details of early steps in the oxidation mechanism of unsaturated hydrocarbons in the troposphere and employ theoretical and experimental techniques. To understand the detailed kinetics of the initial OH addition to unsaturated hydrocarbons, I first present a model developed for the ethylene-OH system. I present the details of a robust two-transition state model. I extend the developed two-transition state model to the case of OH addition to isoprene. Excellent agreement with observed temperature and pressure dependent rate constants affords a high confidence level in understanding of the kinetics and in the calculated branching ratio of the initial OH addition step. I then focus attention on the subsequent reactivity of the OH-isoprene adducts. Until recently, all four of the OH-isoprene adducts were supposed to have reacted with O2 via addition to form alkylperoxy radicals. Previous computational results suggest that two of the OH-isoprene adducts undergo an intramolecular cyclic isomerization followed by hydrogen abstraction by O2 to form stable carbonyl compounds. I have synthesized photolytic precursors, presenting a novel approach to probe the subsequent reactivity of individual hydroxyalkyl radicals. Initial verification of the cyclic isomerization pathway involved synthesis of the photolytic precursor corresponding to the 1,3-butadiene-OH adduct. A culmination of theoretical and experimental techniques allowed verification of the cyclic isomerization pathway. I synthesized the photolytic precursor, which provided a single isoprene-OH adduct. Employing laser photolysis/laser induced fluorescence, time-dependent multiplexed mass spectrometry, velocity map ion imaging, and theoretical techniques, we present the full characterization of the reactivity of the single isoprene-OH adduct in the presence of O2.

Cette thèse porte sur le devenir atmosphérique des Composés Organiques Volatils (COV) oxygénés, utilisés comme solvants, ou additifs aux carburants. Dans ce travail, les premières études cinétiques de réaction avec le radical OH de sept esters ont été effectuées, dans un domaine de température 243-373 K, à l’aide de la technique de Photolyse Laser Pulsée couplée à la Fluorescence Induite par Laser (PLP-FIL). Les constantes de vitesse de réaction des esters étudiés avec le radical OH et l’atome Cl ont également été déterminées par une méthode relative à température ambiante et pression atmosphérique. Pour ces esters, excepté le formate d' isopropyle, le présent travail constitue la première étude de leurs réactions avec l’atome Cl. En utilisant cette même méthode, les réactivités de deux alcools isomères vis à vis de l’atome Cl, en fonction de la température, ont aussi été déterminées. Des mesures de composés carbonylés en air ambiant ont été effectuées à Shanghai et à Pékin en octobre 2009. Les concentrations observées les plus importantes ont été celles de l'acétone, le formaldehyde et l'acétaldehyde. / In this work, kinetic studies for the gas-phase reactions of OH radical with seven saturated esters were firstly carried out, over the temperature range of 243 – 373 K, by using the Pulsed Laser Photolysis- Laser Induced Fluorescence (PLP-LIF) technique. Using the smog chamber technique, the rate coefficients for reactions of the above esters with OH and Cl were also measured at room temperature and one atmosphere. This work provides the first kinetic study for Cl atom reactions with the studied esters except for isopropyl formate. In addition, the temperature dependence of the rate coefficients for Cl reactions with two isomeric alcohols was firstly determined. Atmospheric levels of ambient carbonyl compounds as well as their diurnal variations were investigated during the period of October 2009 in Shanghai and Beijing. The most abundant carbonyls were acetone, followed by formaldehyde and acetaldehyde.

Cigarette smoke is suspected to cause diverse illnesses in smokers and people breathing second- and third-hand smoke. Although different studies have been done to elucidate the impact on health due to smoking, there is a lack of kinetic information regarding the degradation of nicotine under different environmental conditions. As a consequence, currently it is not possible to determine thoroughly the risk due to exposure to nicotine and the compounds derived from its decomposition. With the aim of contributing to clarify the different degradation paths followed by nicotine during and after the consumption of cigarettes, this work presents a theoretical study of the hydrogen atom abstraction reaction by hydroxyl radical at four sites in the nicotine molecule in a broad range of temperature, specifically be-tween 200-3000 K. The site-specific kinetic rate constants were computed by means of the multi-structural torsional variational transition state theory with small curvature tunneling contribution, performing ab initio calculations at the level M06-2X/aug-cc-pVQZ//M06-2X/cc-pVTZ. According to our computations, the dependence on temperature of the studied rate constants exhibited a non-Arrhenius fashion, with a minimum at 873 K. A negative temperature dependence was observed at temperatures lower than 873 K, indicating more prolonged exposure to nicotine in warmer environments. On the other hand, the opposite behavior was observed at higher temperatures; this non-Arrhenius be-havior results of interest in tobacco cigarette combustion, inducing different reaction mechanisms depending on the burning conditions of the different smoking devices. The results indicate that multi-structural and torsional anharmonicity is an im-portant factor in the computation of accurate rate constants, especially at high tem-peratures where the higher-energy conformers of the different species exert a larger influence. The anharmonicity factors suggest that disregarding the anharmonic de-viations leads to overestimation of the rate constant coefficients, by a factor between four and six. Our computed overall kinetic rate constant at 298 K exhibited very good agreement with the only experimental value meausred by Borduas et al. [1], af-fording certainty about our calculated site-specific rate constants, which are currently inaccessible to experiments. However, further experimental studies are necessary to validate our kinetic studies at other temperatures.

The overall aim of this thesis was to investigate the fate of perfluorinated alkyl compounds (PFCs) in biological systems. During the past several years, it has been shown that wildlife are ubiquitously contaminated with two classes of PFCs, the perfluoroalkyl carboxylates (CxF2x+1C(O)OH, PFCAs) and sulfonates (CxF2x+1SO3H, PFSAs). However, there is still considerable uncertainty regarding how wildlife are accumulating these PFCs, particularly in remote areas such as the Canadian arctic. The potential for fluorotelomer acrylate monomers (CxF2x+1CH2CH2OC(O)CH=CH2, FTAcs) to act as precursors to PFCAs through atmospheric oxidation was investigated using smog chamber experiments. FTAc atmospheric fate is determined by OH radical reaction with a lifetime of approximately 1 day. The sole primary product of this reaction was the 4:2 fluorotelomer glyoxylate which is expected to undergo further atmospheric oxidation or photolysis to ultimately yield PFCAs. Temporal and spatial trends of PFCs in arctic ringed seals and seabirds were investigated to assist in understanding PFC transport mechanisms to remote regions. In ringed seals, perfluorooctane sulfonate (PFOS) levels decreased rapidly, coinciding with the phase out by the major manufacturer. These findings are consistent with volatile precursors as the dominant source of PFCs to arctic wildlife. The bioaccumulation and biotransformation of the 8:2 FTAc was investigated in two complimentary studies with rainbow trout. During the in vivo dietary exposure study, fish rapidly accumulated and biotransformed the 8:2 FTAc, with intermediate metabolites observed within 1 hour of dosing. Perfluorooctanoate (PFOA), perfluorononanoate (PFNA) and perfluoroheptanoate (PFHpA) were formed and accumulated in low yields. The carboxylesterase activity in the trout liver and stomach was investigated using in vivo sub-cellular (S9) incubations. Very high esterase activities were shown with approximately equal efficiency in the stomach and liver. The metabolic pathway of the 8:2 fluorotelomer alcohol (8:2 FTOH) was investigated by separately dosing whole rainbow trout with three intermediate metabolites that represented important branching points. The 7:3 fluorotelomer saturated carboxylate (FTCA) did not form PFOA, but formed PFHpA and the 7:3 fluorotelomer unsaturated carboxylate (FTUCA). The 8:2 FTCA and 8:2 FTUCA did form PFOA, confirming a “beta-like-oxidation” mechanism.

The overall aim of this thesis was to investigate the fate of perfluorinated alkyl compounds (PFCs) in biological systems. During the past several years, it has been shown that wildlife are ubiquitously contaminated with two classes of PFCs, the perfluoroalkyl carboxylates (CxF2x+1C(O)OH, PFCAs) and sulfonates (CxF2x+1SO3H, PFSAs). However, there is still considerable uncertainty regarding how wildlife are accumulating these PFCs, particularly in remote areas such as the Canadian arctic. The potential for fluorotelomer acrylate monomers (CxF2x+1CH2CH2OC(O)CH=CH2, FTAcs) to act as precursors to PFCAs through atmospheric oxidation was investigated using smog chamber experiments. FTAc atmospheric fate is determined by OH radical reaction with a lifetime of approximately 1 day. The sole primary product of this reaction was the 4:2 fluorotelomer glyoxylate which is expected to undergo further atmospheric oxidation or photolysis to ultimately yield PFCAs. Temporal and spatial trends of PFCs in arctic ringed seals and seabirds were investigated to assist in understanding PFC transport mechanisms to remote regions. In ringed seals, perfluorooctane sulfonate (PFOS) levels decreased rapidly, coinciding with the phase out by the major manufacturer. These findings are consistent with volatile precursors as the dominant source of PFCs to arctic wildlife. The bioaccumulation and biotransformation of the 8:2 FTAc was investigated in two complimentary studies with rainbow trout. During the in vivo dietary exposure study, fish rapidly accumulated and biotransformed the 8:2 FTAc, with intermediate metabolites observed within 1 hour of dosing. Perfluorooctanoate (PFOA), perfluorononanoate (PFNA) and perfluoroheptanoate (PFHpA) were formed and accumulated in low yields. The carboxylesterase activity in the trout liver and stomach was investigated using in vivo sub-cellular (S9) incubations. Very high esterase activities were shown with approximately equal efficiency in the stomach and liver. The metabolic pathway of the 8:2 fluorotelomer alcohol (8:2 FTOH) was investigated by separately dosing whole rainbow trout with three intermediate metabolites that represented important branching points. The 7:3 fluorotelomer saturated carboxylate (FTCA) did not form PFOA, but formed PFHpA and the 7:3 fluorotelomer unsaturated carboxylate (FTUCA). The 8:2 FTCA and 8:2 FTUCA did form PFOA, confirming a “beta-like-oxidation” mechanism.

The overall aim of this thesis was to investigate the fate of perfluorinated alkyl compounds (PFCs) in biological systems. During the past several years, it has been shown that wildlife are ubiquitously contaminated with two classes of PFCs, the perfluoroalkyl carboxylates (CxF2x+1C(O)OH, PFCAs) and sulfonates (CxF2x+1SO3H, PFSAs). However, there is still considerable uncertainty regarding how wildlife are accumulating these PFCs, particularly in remote areas such as the Canadian arctic. The potential for fluorotelomer acrylate monomers (CxF2x+1CH2CH2OC(O)CH=CH2, FTAcs) to act as precursors to PFCAs through atmospheric oxidation was investigated using smog chamber experiments. FTAc atmospheric fate is determined by OH radical reaction with a lifetime of approximately 1 day. The sole primary product of this reaction was the 4:2 fluorotelomer glyoxylate which is expected to undergo further atmospheric oxidation or photolysis to ultimately yield PFCAs. Temporal and spatial trends of PFCs in arctic ringed seals and seabirds were investigated to assist in understanding PFC transport mechanisms to remote regions. In ringed seals, perfluorooctane sulfonate (PFOS) levels decreased rapidly, coinciding with the phase out by the major manufacturer. These findings are consistent with volatile precursors as the dominant source of PFCs to arctic wildlife. The bioaccumulation and biotransformation of the 8:2 FTAc was investigated in two complimentary studies with rainbow trout. During the in vivo dietary exposure study, fish rapidly accumulated and biotransformed the 8:2 FTAc, with intermediate metabolites observed within 1 hour of dosing. Perfluorooctanoate (PFOA), perfluorononanoate (PFNA) and perfluoroheptanoate (PFHpA) were formed and accumulated in low yields. The carboxylesterase activity in the trout liver and stomach was investigated using in vivo sub-cellular (S9) incubations. Very high esterase activities were shown with approximately equal efficiency in the stomach and liver. The metabolic pathway of the 8:2 fluorotelomer alcohol (8:2 FTOH) was investigated by separately dosing whole rainbow trout with three intermediate metabolites that represented important branching points. The 7:3 fluorotelomer saturated carboxylate (FTCA) did not form PFOA, but formed PFHpA and the 7:3 fluorotelomer unsaturated carboxylate (FTUCA). The 8:2 FTCA and 8:2 FTUCA did form PFOA, confirming a “beta-like-oxidation” mechanism.

The overall aim of this thesis was to investigate the fate of perfluorinated alkyl compounds (PFCs) in biological systems. During the past several years, it has been shown that wildlife are ubiquitously contaminated with two classes of PFCs, the perfluoroalkyl carboxylates (CxF2x+1C(O)OH, PFCAs) and sulfonates (CxF2x+1SO3H, PFSAs). However, there is still considerable uncertainty regarding how wildlife are accumulating these PFCs, particularly in remote areas such as the Canadian arctic. The potential for fluorotelomer acrylate monomers (CxF2x+1CH2CH2OC(O)CH=CH2, FTAcs) to act as precursors to PFCAs through atmospheric oxidation was investigated using smog chamber experiments. FTAc atmospheric fate is determined by OH radical reaction with a lifetime of approximately 1 day. The sole primary product of this reaction was the 4:2 fluorotelomer glyoxylate which is expected to undergo further atmospheric oxidation or photolysis to ultimately yield PFCAs. Temporal and spatial trends of PFCs in arctic ringed seals and seabirds were investigated to assist in understanding PFC transport mechanisms to remote regions. In ringed seals, perfluorooctane sulfonate (PFOS) levels decreased rapidly, coinciding with the phase out by the major manufacturer. These findings are consistent with volatile precursors as the dominant source of PFCs to arctic wildlife. The bioaccumulation and biotransformation of the 8:2 FTAc was investigated in two complimentary studies with rainbow trout. During the in vivo dietary exposure study, fish rapidly accumulated and biotransformed the 8:2 FTAc, with intermediate metabolites observed within 1 hour of dosing. Perfluorooctanoate (PFOA), perfluorononanoate (PFNA) and perfluoroheptanoate (PFHpA) were formed and accumulated in low yields. The carboxylesterase activity in the trout liver and stomach was investigated using in vivo sub-cellular (S9) incubations. Very high esterase activities were shown with approximately equal efficiency in the stomach and liver. The metabolic pathway of the 8:2 fluorotelomer alcohol (8:2 FTOH) was investigated by separately dosing whole rainbow trout with three intermediate metabolites that represented important branching points. The 7:3 fluorotelomer saturated carboxylate (FTCA) did not form PFOA, but formed PFHpA and the 7:3 fluorotelomer unsaturated carboxylate (FTUCA). The 8:2 FTCA and 8:2 FTUCA did form PFOA, confirming a “beta-like-oxidation” mechanism.

Iron bioavailability of diets containing oxidized turkey and oxidized beef meat was investigated in two experiments. In both vi studies male, weanling rats were made anemic by consumption of a low iron diet and bleeding. The experimental diets were prepared so that meat was the only source of iron. Hemoglobin regeneration served as the basis for measuring iron utilization. In experiment 1, lyophilized, uncooked turkey meat was allowed to oxidize at 20-22°C for 0, 48, 96, 144, 216, or 264 hours and then fed to the rats. The length of oxidation time of the turkey meat did not significantly affect the growth of the rats or the bioavailability of the meat iron. In experiment 2, lyophilized, uncooked beef was allowed to oxidize at 20-22°C for 14 days. Anemic rats were fed diets composed of basal, basal + iron, basal + iron + formaldehyde, 100% fresh beef, 75% fresh 25% oxidized beef, 50% fresh-50% oxidized beef, 25% fresh-75% oxidized, 100% oxidized beef and 100% fresh beef + formaldehyde. Rats fed severely oxidized beef diets had decreased body weight, enlarged livers and depressed hematinic responses. Formaldehyde did not significantly affect iron utilization in rats fed basal diets, but depressed liver iron storage in rats fed fresh beef. A third experiment to further compare the chemical properties of uncooked, lyophilized hand deboned and mechanically deboned beef and turkey meat was performed. Analysis by the Thiobarbituric Acid Method, Formaldehyde Value, and Iodine Number indicated increased sophistication of testing methods for lyophilized meats needs to be developed. Although the Thiobarbituric Acid Method was successfully used in Experiment 1, unreliable results were obtained using this method in Experiment 3. It is assumed that this variability in results is due to using the Thiobarbituric Acid Method with a dry system. The problems encountered with the Formaldehyde Value included contamination of the water supply with aldehydes and unreliable reagent. The Iodine Number was unreliable used on meat samples. Possibly the fat could be extracted from the meat under cool nitrogen to prevent further oxidation of the fat. Then the iodine number could be determined on the extracted fat.

Over the last decade our understanding of mercury cycling has dramatically changed. Evidence of rapid atmospheric oxidation has been observed in the Arctic, Antarctic, the MBL, coastal environments, saline lakes, and the upper troposphere/lower stratosphere. These results show that, Hg0, can undergo rapid gas-phase oxidation under standard atmospheric conditions. However, the mechanism and importance of this transformation is still unclear. The goal of this work was two-fold: to investigate of the kinetics of potential pathway for the gas phase oxidation of atmospheric mercury and to develop new laser based techniques, which can be employed for both laboratory and field studies of Hg(0) and the products of mercury oxidation. First and foremost, this work determined kinetic rate coefficients for the potentially important mercury reactions. Rate coefficients were determined using a Pulse Laser Photolysis - Laser Induced Fluorescence (PLP-LIF) technique monitoring one or more of the following species, Hg(0), Cl, Br, HgCl, and HgBr. The concentrations of these species were measured by LIF as the reaction occurred and a concentration vs. time profile was generated. From these profiles a rate coefficient for the reaction can be obtained. In the course of this work kinetic rate coefficients for the following mercury reactions were measured. Hg(0) + Cl + M --> HgCl + M Hg(0) + Br + M --> HgBr + M HgBr + M --> Hg(0) + Br + M HgBr + Br --> products HgCl + O2 --> products This work is the first direct measurement of a kinetic rate coefficient for these reactions, and the first work which employed one photon LIF to monitor the HgCl and HgBr products. The second aspect of this work was the development of new laser based techniques to detect atmospheric mercury and its oxidation products for both laboratory and field application. In this work a LIF technique was develop to detect HgCl and HgBr. In addition, a two photon LIF technique initially developed by Bauer et al., 2002 was verified and expanded. The two photon LIF technique was used to directly monitor Hg(0) atoms in-situ, to monitor Hg(0) evolving form a gold tube, and to monitor the Hg(0) evolving from the thermal decomposition of reactive gaseous mercury collected on a KCl coated or uncoated denuder. This work represents a significant advance in the development of a viable method the detect mercury and the mercury oxidation products in the laboratory and in the field and is the first study to observe clear differences in the characteristic desorption profiles of HgO and HgX2. This work has broad implications, it enhanced our current knowledge concerning the biogeochemical cycling of mercury, broadened our understanding of the mercury chemistry in high halogen environment, and provided new techniques which can be applied in future field and laboratory studies.

Mechanistic aspects of carbonaceous aerosol toxicity were examined with respect to the ability of particles to catalyse reactive oxygen species-generating redox cycling reactions. To investigate the role of secondary organic material, we examined two systems. In the first, two-stroke engine exhaust particles were found to increase their ability to catalyse redox cycling in the presence of a reducing agent, dithiothreitol (DTT), when the exhaust was exposed to ozone. This occurred through deposition of redox-active secondary organic aerosol (SOA) onto the particle that was ten times more redox active per microgram than the primary engine particle. In the second system, naphthalene SOA formed highly redox active particles. Activity was strongly correlated to the amount of the 1,4- and 1,2-naphthoquinone measured in the particle phase. However, these species and the newly quantified naphthalene oxidation product 5-hydroxy-1,4-naphthoquinone accounted for only 30% of the observed DTT decay from the particles. Gas-particle partitioning coefficients suggest 1,4- and 1,2-naphthoquinone are not strong contributors to ambient particle redox activity at 25°C. However, a large number of redox active species are unidentified. Some of these may be highly oxidised products of sufficiently low vapour pressure to be atmospherically relevant. DTT activity of diesel particles was found to be high per unit mass. The activity was found to be associated with the insoluble fraction as filtration of the particles nearly eliminated DTT decay. Neither methanol nor dichloromethane extracts of diesel particles exhibited redox activity, indicating that the redox active species are associated with the black carbon portion of the particles. Examination of particle concentration techniques found that use of water condensation to grow and concentrate particles introduced a large organic artefact to the particles. Experiments with concentrated inorganic particles suggest that the source of this artefact is from irreversible uptake of water-soluble volatile organic compounds. Overall, carbonaceous redox active species can be thought of as a continuum from small, water-soluble species to redox active functionalities on elemental carbon backbones. In addition to clearly defined, quantifiable species, future research may need to consider examining broader chemical classes or redox-active chemical functionalities to overcome the inherent complexity of these constituents.