Heterogeneous reactions between mineral dust aerosols and gas phase volatile organic compounds have the potential to impact important atmospheric chemical processes. However, little is known about the uptake and reactivity of volatile organic compounds on particulates found in the environment. A Knudsen cell was designed and constructed for providing precise measurement of reaction probabilities within these systems. The instrument was validated through a series of experiments. After validating the Knudsen cell against several key benchmarks, the instrument was used to measure the uptake coefficient for ethanol on particulate silicon dioxide. The uptake coefficient of ethanol on silicon dioxide, a common compound in mineral dust aerosols, was determined to be 7 x 10-7. Therefore, uptake of ethanol on silicon dioxide would be competitive with the loss of other volatile organic compounds on silicon dioxide, which show similar rates of uptake. The Knudsen cell was validated and measured the uptake of ethanol on silicon dioxide, and future work with the Knudsen cell will study the uptake of chemical warfare agent simulants on metal oxides. / Master of Science

The hydrolysis reaction of N2O5 was investigated at room temperature on two aerosol types using a flow tube coupled to a newly built Chemical Ionization Mass Spectrometer (CIMS). This instrument was fully constructed and optimized during this research period, as well as employed to conduct one of two aerosol studies. The first examined the reaction on ammonium bisulphate aerosols using a new ion detection method, I-•N2O5 cluster formation, which proved to be highly advantageous over the common approach of dissociative charge transfer, yielding a sensitivity for I-•N2O5 of 0.024 Hz/pptv. The uptake coefficients at 30% and 50% relative humidity were 0.0067 ± 0.0002 and 0.0120 ±0.0014, respectively. The second study was performed using a different CIMS previously assembled in the laboratory. In this case, the reaction was investigated on secondary organic aerosols produced through the ozonolysis of α-pinene, and resulted in an uptake coefficient of 8.5x10-5 ± 7x10-6 at 0% relative humidity.

The hydrolysis reaction of N2O5 was investigated at room temperature on two aerosol types using a flow tube coupled to a newly built Chemical Ionization Mass Spectrometer (CIMS). This instrument was fully constructed and optimized during this research period, as well as employed to conduct one of two aerosol studies. The first examined the reaction on ammonium bisulphate aerosols using a new ion detection method, I-•N2O5 cluster formation, which proved to be highly advantageous over the common approach of dissociative charge transfer, yielding a sensitivity for I-•N2O5 of 0.024 Hz/pptv. The uptake coefficients at 30% and 50% relative humidity were 0.0067 ± 0.0002 and 0.0120 ±0.0014, respectively. The second study was performed using a different CIMS previously assembled in the laboratory. In this case, the reaction was investigated on secondary organic aerosols produced through the ozonolysis of α-pinene, and resulted in an uptake coefficient of 8.5x10-5 ± 7x10-6 at 0% relative humidity.

La poussière minérale est l'aérosol le plus abondant injecté dans l'atmosphère. Les surfaces de poussière peuvent être le siège de phénomènes d‘adsorption et de transformation hétérogène de gaz traces et peuvent affecter la teneur en espèces clés atmosphériques. Dans ce contexte, l'objectif de ce travail était l'étude expérimentale de la réactivité de particules minérales avec des gaz traces atmosphériques. L'interaction de réactifs gazeux (NO2, HONO, H2O2, OH, HO2) avec des oxydes minéraux (TiO2, Al2O3, Fe2O3, Arizona Test Dust) a été étudiée à l'aide d'un photoréacteur mis en place dans le cadre de la thèse pour des études de processus hétérogènes photochimiques. Le photoréacteur consiste en un tube à écoulement (irradié par 6 lampes UV) à basse pression (quelques Torr), couplé à l‘analyse des espèces par un spectromètre de masse quadripolaire à ionisation par impact électronique. Les coefficients de capture (ou probabilité de perte d'une espèce gazeuse par collision avec la surface réactive) ainsi que les produits de réactions hétérogènes ont été déterminés en fonction de différents paramètres tels que la masse du film minéral, la concentration initiale du réactif gazeux, la température, l‘humidité relative, la concentration d'oxygène et l'intensité d'irradiation UV. Les mécanismes des processus hétérogènes étudiés et leurs implications atmosphériques ont été discutés. En particulier, les données obtenues indiquent que la contribution de l'aérosol à la perte totale de HONO dans la couche limite planétaire est négligeable. A l‘inverse, l'interaction de H2O2 et des radicaux HO2 avec des aérosols minéraux peut être un puits non négligeable d'espèces HOx (OH, HO2) dans la troposphère avec un effet sur le pouvoir oxydant de la troposphère. / Mineral dust is the most abundant aerosol injected into the atmosphere. The dust surfaces provide the seedbed for adsorption and heterogeneous transformation of trace gas molecules and can affect the content of key atmospheric species. In this context, the goal of the present work was the experimental investigation of the reactivity of mineral dust particles toward trace atmospheric gases. The interaction of gaseous reactants (NO2, HONO, H2O2, OH, HO2) with mineral oxides (TiO2, Al2O3, Fe2O3, Arizona Test Dust) was studied using a photoreactor developed during this work for studies of heterogeneous photochemical processes. The photoreactor comprises a low pressure (several Torr) flow reactor (irradiated with 6 UV lamps) combined with an electron impact ionization quadrupole mass spectrometer for analysis of gas phase species. The uptake coefficients (determined as the probability of gas species loss per collision with reactive surface) as well as the products of heterogeneous reactions were determined as a function of different parameters such as the mass of mineral film, initial concentration of the gaseous reactant, temperature, relative humidity, concentration of oxygen and UV irradiation intensity. The mechanisms of the heterogeneous processes studied and their atmospheric implications are discussed. In particular, the data obtained in the present work indicate that the contribution of the aerosol to the total loss of HONO in the planetary boundary layer is negligible. Instead, the interaction of H2O2 and of HO2 radicals with mineral aerosols may be an important sink for HOX (OH, HO2) species in the troposphere with an effect on the oxidative capacity of the troposphere.

Du fait de l’omniprésence de l’homme au sein du compartiment intérieur, y passant jusqu’à 90% de son temps au cours d’une journée, il est devenu essentiel de caractérisé correctement l’atmosphère et donc les polluants présent dans ce milieu. Ce travail de thèse prend la suite d’une étude menée au sein de notre laboratoire montrant une importante présence de radicaux hydroxyles dans cette atmosphère. Le polluant précurseur des radicaux supposé au cours de cette étude est l’acide nitreux (HONO), présent dans des quantités de l’ordre du ppb pour l’intérieur. Ce travail de thèse a donc eu pour but, dans un premier temps de caractériser la photolyse de l’acide nitreux conduisant à la formation de radicaux hydroxyles, et dans un second temps d’établir ses différentes voies de formation, directes et indirectes, afin de quantifier ses sources dans les atmosphères intérieures. / People in Western societies spend about 90% of their time indoors, predominantly within indoor places. The residence time of the airborne indoor pollutants is much longer due to the smaller volumes compared to the outdoor atmosphere and low air exchange rates. Therefore, a comprehensive understanding of indoor air quality is essential.Nitrous acid (HONO) is an emerging indoor pollutant because 1) it can lead to human respiratory tract irritation and formation of carcinogenic nitrosamines, and 2) it can be effectively photolyzed leading to a pulse of hydroxyl radicals (OH).The PhD work here presented is focused on understanding of the formation processes of oxidizing species such as HONO and, hence, OH radicals in the built environment.