Le secteur des transports est fondamental pour le développement économique d'un pays et pour assurer la communication et une bonne qualité de vie. Cependant, le transport routier conduit à une grave dégradation de la qualité de l'air et contribue au réchauffement de la planète. Parmi tous les polluants, les particules fines et ultrafines, émises par les véhicules mais également formées dans l'atmosphère sont considérées toxiques. De nombreuses études montrent que l’exposition chronique aux particules fines favorise le développement de pathologies respiratoires et cardiovasculaires. Les précurseurs gazeux, les principaux mécanismes réactionnels ainsi que les transformations physiques que les Aérosol Organiques Secondaires (AOS) subit dans l'atmosphère restent encore incertains. La présente étude porte principalement sur la caractérisation des polluants primaires émis par les échappements automobiles et les transformations photochimiques des COV / COVI. Les émissions des voitures ont été évaluées à l’aide d’un banc à rouleau au laboratoire de l’IFSTTAR. Les mesures du nombre de particules ont été effectuées directement au niveau de l’échappement. Pour les véhicules GDI, PN0.23 (<23 nm) représentait en moyenne 20- 30% du nombre total de particules émises, alors que pour les voitures diesel, cette fraction était bien inférieure (≈10-15%). Lors des régimes à grande vitesse (autoroutier Artemis) des véhicules diesel, une régénération passive de Filtre à Particules (FAP) a été observée. Les particules émises étaient principalement constituées de suie, de bisulfate et de matière organique. Les particules émises par les voitures essence à injection directe étaient principalement composées de Black Carbon (BC) et de gouttelettes organiques contenant des éléments. Pendant le démarrage à froid, les voitures GDI émettent des concentrations importantes de BC et de matière organique. Les émissions d'hydrocarbures ont également été étudiées. Les véhicules GDI ont émis des concentrations importantes de THC lors du démarrage à froid. Parmi les composés aliphatiques, des composés jusqu’à la C15 ont été identifiés, confirmant l’émission d'hydrocarbures plus lourds par les voitures diesel. La deuxième partie de ce travail consistait à étudier la transformation atmosphérique de certains COV (toluène, naphtalène, cyclohexane, nonane) émis par les véhicules Euro 5 et Euro 6 et à déterminer le potentiel de formation d’AOS de ces composés. Les composés choisis ont été photo-oxydés (seuls et en mélange) dans un réacteur à tube à flux d'aérosol afin de simuler leur vieillissement atmosphérique. Les résultats majeurs suggèrent: (1) des composés aromatiques et des HAP représentent les composés avec le plus fort potentiel de formation d'AOS ; (2) la température a un impact important sur la formation et le rendement d'AOS ; (3) la présence de particules préexistantes a un effet positif sur la formation d'AOS; (4) il a été constaté que la présence des NOx affectaient négativement la formation d'AOS ; (5) la formation d'AOS de mélanges de COV est fortement influencée par la fraction de composé aromatique. Certains des produits identifiés dans la phase particulaire n’ont jamais été signalés auparavant. La dégradation des composés aromatiques en régime de NOx moyen a produit des composés nitro-aromatiques identifiés à la fois en phase gazeuse et en phase particulaire. Cette thèse contribue à enrichir la base de données d’émissions des voitures, encore limitée aux véhicules Euro 5 et Euro 6. La spéciation des composés non réglementés aidera à mieux comprendre le budget atmosphérique d’AOS et les impacts des voitures sur la qualité de l’air. Enfin, l’étude de photoxydation de COV primaires (seuls, mélange et émissions complètes) conduira à une meilleure compréhension de la formation d’AOS / The transport sector is fundamental to the economic development of a country and to ensure communication and a good quality of life. However, road transport contributes significantly to global warming and leads to serious degradation of the air quality. Among all pollutants, fine and ultrafine particles, emitted by vehicles but also formed in the atmosphere are considered as potentially toxic. Many studies show that chronic exposure to fine particles promotes the development of respiratory and cardiovascular diseases. The main gaseous precursors, the atmospheric chemical pathways as well as the chemical composition and the physical transformations that secondary organic aerosol (SOA) undergo in the atmosphere, remain poorly understood. The main aim of this work was on one side to improve the knowledge about primary pollutants emitted from Euro 5 and Euro 6 diesel and gasoline passenger cars and on the other side to investigate the photochemical transformations of the VOCs/IVOCs emitted from these cars. Passenger car emissions have been evaluated on a chassis dynamometer test bench at the IFSTTAR laboratory. Particle number measurements were carried out directly at the tailpipe. For GDI vehicles PN0.23 (< 23 nm) represented on average 20 -30 % of total particle number emitted, while for diesel cars, this fraction was considerably lower (≈10-15%). During high speed regimes (Artemis motorway) of diesel passenger cars Diesel Particulate Filter (DPF) passive regeneration was observed. These periods were characterized by a high particle number concentration; their composition was mainly soot, bisulfate and some organic material. PM emitted from gasoline DI passenger cars was mainly composed by BC and some organic droplets containing traces of other elements. During cold start GDI cars do emit important concentrations of BC and organic material. Emission of hydrocarbons has also been investigated. Gasoline DI emitted important concentration of THCs during cold start. Among the aliphatic compounds, families until C15 have been identified, confirming emission of heavier HCs from diesel cars. The second aim of this work was the study of atmospheric degradation of selected VOCs (toluene, naphthalene, cyclohexane, nonane) emitted from Euro 5 and Euro 6 vehicles and to determine the SOA formation potential of these compounds under different environmental conditions. The chosen compounds have been photoxidized (alone and in mixture) in an Aerosol Flow Tube (AFT) reactor in order to simulate VOCs atmospheric aging. The results suggest: (1) aromatic and PAHs compounds, own highest potential to form SOA; (2) the temperature has an important impact on SOA formation and yield; (3) the presence of pre-existing seed particles has, in general, a positive effect on SOA formation and (4) NOx has been found to negatively affect SOA formation; (5) SOA potential formation of VOC mixtures is highly influenced by the fraction of aromatics. Some of the products identified in the particle phase have never been previously reported. Degradation of aromatic compounds under medium NOx regime produced nitro-aromatic compounds identified both in the gas and particle phase. This PhD contributes to enrich vehicle emissions database, still limited for Euro 5 and Euro 6 cars. Speciation of non-regulated compound will help to better understand atmospheric SOA budget and car emissions air quality impacts. By last, the photoxidation study of primary VOCs (alone, mixture and full emissions) will lead to a better comprehension of SOA formation from vehicles

Les aérosols organiques (AO), issus de nombreuses sources et de différents processus atmosphériques, ont un impact significatif sur la qualité de l’air et le changement climatique. L’objectif de ce travail de thèse était d’acquérir une meilleure connaissance de l’origine des AO par l’utilisation de marqueurs organiques moléculaires au sein de modèles source-récepteur de type positive matrix factorization (PMF). Ce travail expérimental était basé sur deux campagnes de prélèvements réalisées à Grenoble (site urbain) au cours de l’année 2013 et dans la région parisienne (site péri-urbain du SIRTA, 25 km au sud-ouest de Paris) lors d’un intense épisode de pollution aux particules (PM) en Mars 2015. Une caractérisation chimique étendue (de 139 à 216 espèces quantifiées) a été réalisée et l’utilisation de marqueurs moléculaires primaires et secondaires clés dans la PMF a permis de déconvoluer de 9 à 11 sources différentes de PM10 (Grenoble et SIRTA, de façon respective) incluant aussi bien des sources classiques (combustion de biomasse, trafic, poussières, sels de mer, nitrate et espèces inorganiques secondaires) que des sources non communément résolues telles que AO biogéniques primaires (spores fongiques et débris de plantes), AO secondaires (AOS) biogéniques (marin, oxydation de l’isoprène) et AOS anthropiques (oxydation des hydrocarbures aromatiques polycycliques (HAP) et/ou des composés phénoliques). En outre, le jeu de données obtenu pour la région parisienne à partir de prélèvements sur des pas de temps courts (4h) a permis d’obtenir une meilleure compréhension des profils diurnes et des processus chimiques impliquées. Ces résultats ont été comparés à ceux issus d’autres techniques de mesures (en temps réel, ACSM (aerosol chemical speciation monitor) et analyse AMS (aerosol mass spectrometer) en différée) et/ou d’autres méthodes de traitement de données (méthodes traceur EC (elemental carbon) et traceur AOS). Un bon accord a été obtenu entre toutes les méthodes en termes de séparation des fractions primaires et secondaires. Cependant, et quelle que soit l’approche utilisée, la moitié de la masse d’AOS n’était toujours pas complètement décrite. Ainsi, une nouvelle approche d’étude des sources de l’AO a été développée en combinant les mesures en temps réel (ACSM) et celles sur filtres (marqueurs moléculaires organiques) et en utilisant un script de synchronisation des données. L’analyse PMF combinée a été réalisée sur la matrice de données unifiée. 10 facteurs AO, incluant 4 profils chimiques différents en lien avec la combustion de biomasse, ont été mis en évidence. Par rapport aux approches conventionnelles, cette nouvelle méthodologie a permis d’obtenir une meilleure compréhension des processus atmosphériques liés aux différentes sources d’AO. / Organic aerosols (OAs), originating from a wide variety of sources and atmospheric processes, have strong impacts on air quality and climate change. The present PhD thesis aimed to get a better understanding of OA origins using specific organic molecular markers together with their input into source-receptor model such as positive matrix factorization (PMF). This experimental work was based on two field campaigns, conducted in Grenoble (urban site) over the 2013 year and in the Paris region (suburban site of SIRTA, 25 km southwest of Paris) during an intense PM pollution event in March 2015. Following an extended chemical characterization (from 139 to 216 species quantified), the use of key primary and secondary organic molecular markers within the standard filter-based PMF model allowed to deconvolve 9 and 11 PM10 sources (Grenoble and SIRTA, respectively). These included common ones (biomass burning, traffic, dust, sea salt, secondary inorganics and nitrate), as well as uncommon resolved sources such as primary biogenic OA (fungal spores and plant debris), biogenic secondary AO (SOA) (marine, isoprene oxidation) and anthropogenic SOA (polycyclic aromatic hydrocarbons (PAHs) and/or phenolic compounds oxidation). In addition, high time-resolution filter dataset (4h-timebase) available for the Paris region also illustrated a better understanding of the diurnal profiles and the involved chemical processes. These results could be compared to outputs from other measurement techniques (online ACSM (aerosol chemical speciation monitor), offline AMS (aerosol mass spectrometer) analyses), and/or to other data treatment methodologies (EC (elemental carbon) tracer method and SOA tracer method). A good agreement was obtained between all the methods in terms of separation between primary and secondary OA fractions. Nevertheless, and whatever the method used, still about half of the SOA mass was not fully described. Therefore, a novel OA source apportionment approach has finally been developed by combining online (ACSM) and offline (organic molecular markers) measurements and using a time synchronization script. This combined PMF analysis was performed on the unified matrix. It revealed 10 OA factors, including 4 different biomass burning-related chemical profiles. Compared to conventional approaches, this new methodology provided a more comprehensive description of the atmospheric processes related to the different OA sources.

À cause de leur diffusion et de leur absorption des radiations solaires, les aérosols atmosphériques jouent un rôle important dans l'évolution du climat terrestre. Les techniques de mesure actuelles apportent certes, des connaissances, sur le forçage radiatif mais les résultats possèdent généralement de larges incertitudes, souvent du même ordre de grandeur que la valeur elle-même. Ces incertitudes sont causées par le manque de précision sur les données liées aux propriétés optiques estimées de ces aérosols (comme l'absorption, la diffusion ou l'extinction). Elles découlent principalement des techniques de mesures actuelles : à l'effet de chargement des filtres (lors de mesures classiques par filtres), aux mesures limitées par l'étendue spectrale des instruments, aux conditions d'échantillonnage différents lors de mesures séparées, etc. Dans ce travail de thèse, j'ai développé puis testé des instruments optiques et électroniques dans le but d'augmenter la précision des mesures des coefficients d'extinction et d'absorption des aérosols. (1) Deux spectrophones PhotAccoustique (PA) sont développés afin d'améliorer les mesures d'absorption des aérosols grâce à des mesures directes et sans filtres. Une première génération utilisant un rayonnement à 444 nm permet de réduire les incertitudes de mesure de 20-30% (obtenue par la technique d'échantillonnage par filtres) à 7,4% et 4,6% pour la détermination des coefficients d'absorption massique du carbone suie et de cendres volcaniques, respectivement. Transformé en spectrophone PA à multi-longueurs d'onde opérant conjointement à 444,532 et 660 nm, il permet alors de caractériser la dépendance spectrale du Coefficient d'Absorption d'Ångström (CAA). Les valeurs du CAA du carbone suie sont en accord avec les résultats publiés. Celles obtenues lors de l'analyse de deux échantillons de cendres volcaniques résultant de l'éruption du Eyjafjallajökull sont similaires au CAA du carbone brun,prouvent la présence d'importantes quantités d'éléments organiques. (2) Un extinctiomètre, basé sur le principe de la spectroscopie d'absorption en cavité à source large bande et incohérente (IBBCEAS), est ensuite développé afin de suivre l'évolution des propriétés optiques d'Aérosols Organiques Secondaires (AOS) produits par la photolyse du 2-nitrophénol dans une chambre de simulation atmosphérique de l'University College de Cork (Irlande). Leurs coefficients d'extinction et d'absorption sont suivis par cet extinctiomètre et un spectrophone PA durant tout le processus de production. Les évolutions des propriétés optiques des AOS confirment l'effet du vieillissement atmosphérique. (3) Une nouvelle architecture de détection synchrone est développé afin de rendre notre prototype plus léger, plus compact, mieux adapté aux applications in situ et plus particulièrement aux drones, techniques émergentes qui permettent de caractériser le profil vertical des aérosols dans l'atmosphère. Cette détection synchrone innovante, évaluée lors de la mesure de la concentration de NO₂ ambiant (niveau de concentration de quelques ppbv) possède une précision et une reproductibilité de mesures comparable à la détection synchrone SR830, commercialisée par la société Stanford Research Inc. L'évaluation précise de l'impact climatique des aérosols nécessite une quantification exacte et non biaisée de leurs propriétés optiques. À ce jour, elle reste un défi majeur dans la recherche sur les sciences de l'atmosphère et du changement climatique. Ainsi, des informations sur la taille des particules (liée à l'absorption sélective en longueur d'onde) nécessitent des mesures étendues sur de larges régions spectrales du rayonnement solaire principale. Le développement d'un albédomète large bande à haute précision, dédié à la mesure simultanée des coefficients d'extinction et d'absorption des aérosols est en cours. / Atmospheric aerosols are known to play an important role in earth climate by scattering and absorbing solar radiation. However, the aerosol radiative forcing effect is still known with large uncertainties (almost equal to the magnitude of the aerosol radiative forcing). The uncertainties are mainly caused by inaccurate estimates of aerosol optical properties (such as its absorption, scattering and extinction coefficients) using the currently available measurement techniques, with result in filter loading effect in classic filter technique, the uncertainty due to different sampling conditions for separate measurements of aerosol optical properties in combination of different techniques or due to the measurements at limited spectral wavelength ranges. My PhD work was carried out on the developments and applications of optical and electronic instruments for accurate measurements of aerosol extinction and absorption coefficient : (1) Photoacoustic spectrophones were developed for filter-free direct measurements of aerosol absorption with high accuracy. Measurements uncertainties down to about 7.4% and 4.6% (compared to about 20-30% in filter-based measurements) were achieved for the determination of mass absorption coefficients of black carbon and volcanic ash samples, respectively, using a single-wavelength PA spectrophone operating at 444 nm. A 3-wavelength PA spectrophone operating at 444,532 and 660 nm was developed and deployed for characterizing wavelength-dependent optical properties of aerosol absorption Ångström coefficient (AAC). The determined AAC of black carbon was well consistent with the previously reported value. Our AAC values of two volcanic ash samples from 2010 eruptions of Eyjafjallajökull, similar to the AAC of brown carbon, indicated abundant organic compounds in the volcanic ash samples. The developed multi-wavelength PA spectrophone was tested and validated in an intensive field campaign measurements of environmental particles in Grenoble (France). Side-by-side inter-comparison measurements using an aethalometer showed a lineat correlation of the measured aerosol absorption coefficients from both instruments. (2) An extinctiometer based on IBBCEAS was developed for study of optical properties of secondary organic aerosol (SOA) produced from photolysis of 2-nitrophenol in an atmospheric simulation chamber at University College Cork (Ireland). Simultaneous monitoring of the SOA extinction and absorption (in conjuction with a PA spectrophone) coefficients was performed during its whole production process, the measured evolutions of the SOA optical properties highlighted the atmospheric aging effect. (3) In order to render optical sensor lightweight and suitable for field applications, in particular for the newly emerging unmanned aerial vehicle (UAV) applications, a novel architecture of lock-in amplifier (LIA) was proposed and developed in the framework of this Phd Research. The novel LIA, evaluated with an inter-comparison measurement of ambient NO₂ at the ppbv concentration level, shows an identical performance (in terms of measurements accuracy and precision) as the widely used commercial LIA (SR830, Stanford Research Inc.), while using a simplified and lightweight hardware architecture. Evaluation of the aerosol impact on climate requires accurate and unbiased quantification of the its wavelength-dependent optical properties over a wide spectral region of the major solar radiation, which can provide information on particle size (due to the wavelength dependence of scattering by fine particles) as well as insights on aerosol chemical composition (because of its wavelength selective absorption). To date, it is still a key challenge in atmospheric science and climate change research. Development of a broadband aerosol albedometer is ongoing, which is dedicated to simultaneous measurements of aerosol extinction and absorption coefficients with high-accuracy and high-precision.

The influence of chemical mechanisms and meteorological parameterizations on pollutant concentrations calculated with an air quality model is studied. The influence of the differences between two gas-phase chemical mechanisms on the formation of ozone and aerosols in Europe is low on average. For ozone, the large local differences are mainly due to the uncertainty associated with the kinetics of nitrogen monoxide (NO) oxidation reactions on the one hand and the representation of different pathways for the oxidation of aromatic compounds on the other hand. The aerosol concentrations are mainly influenced by the selection of all major precursors of secondary aerosols and the explicit treatment of chemical regimes corresponding to the nitrogen oxides (NOx) levels. The influence of the meteorological parameterizations on the concentrations of aerosols and their vertical distribution is evaluated over the Paris region in France by comparison to lidar data. The influence of the parameterization of the dynamics in the atmospheric boundary layer is important ; however, it is the use of an urban canopy model that improves significantly the modeling of the pollutant vertical distribution

This thesis describes the investigation of three aspects of the formation of secondary organic aerosol (SOA): * Aerosol formation from mixed precursors * Global modelling of SOA formation * Modelling of dynamics of SOA formation based on empirical data collected from smog chamber experiments. The formation and growth processes of secondary organic aerosol were investigated using smog chamber experimentation and modelling techniques to gain a better understanding of the application of SOA yield values in modelling both SOA mass and dynamics. Published SOA yields from a range of volatile organic compounds (VOCs) are used to model SOA mass on a local, regional or global scale, based on the assumption that the SOA yield of a mixture is the sum of the yields of the components. Experimental investigations into SOA yield from mixtures of VOC revealed potential uncertainties that would result from applying these yields to systems containing multiple VOCs. SOA formation in systems of toluene or m-xylene, compared with systems of these VOCs and propene, have shown that the introduction of propene (which has a zero SOA yield) to smog chamber photo-oxidations of toluene or m-xylene delays the formation and suppresses the overall yield of SOA from 450 to 90 µg m-3 ppm-1 for the toluene system and from 325 to 125 µg m-3 ppm-1 for the mvxylene system compared with systems of individual species without propene. The SOA partitioning yield data also indicates that partitioning of species to existing aerosol is suppressed in the mixed systems. Gas-phase modelling of these experiments showed that potential SOA species were expected to be formed sooner due to the increased system reactivity provided by propene. The observed delay in SOA nucleation, similar consumption rates of toluene and m-xylene in both the single and mixed systems and the gas-phase modelling results suggest that the addition of propene to hydrocarbon SOA systems modifies the gas-phase chemistry leading to the formation of potential SOA species from toluene and m-xylene. This result calls into question the bulk and partitioning yield values that have been published for pure substances as well as the validity of applying individual VOC yields to VOC mixture. Application of SOA yields to the global scale provides estimates of annual global SOA formation, global contributions from various VOCs and regional SOA distributions. Two SOA modules, using bulk and partitioning yield methods, were added to a global atmospheric chemical transport model, MOZART-2. The bulk yield method, representing the maximum possible global SOA burden, gave an annual production of 24.5 Tg of SOA, which is slightly lower than previous estimates (30 - 270 Tg yr-1). The partitioning method, which gives a more realistic estimate of SOA formation, produced 15.3 Tg yr-1; the biogenic fraction (13.6 Tg yr-1) compares to a previous estimate of biogenic SOA of 18.5 Tg yr-1 and 2.5 to 44 Tg yr- 1 using the partitioning method. Anthropogenic SOA contributions of 1.1 Tg yr-1 from MOZART-2 compared to recent estimates of 0.05 -2.62 Tg yr-1. SOA production was found to be dependent on oxidant availability and VOC emissions in South America and Asia. The partitioning method produced significantly less SOA due to limited availability of OC. Thepartitioning method also produced a peak SOA concentration of 10 µg m-3 over South America in September and showed that SOA is at maximum production for most of the year in Asia and Europe. The two SOA formation methods also provides data to analyse the restrictions to SOA formation in particular regions, based on the maximum amount of SOA able to form (bulk yield method) and the more realistic partitioning estimate from the same region. Limitations to SOA formation in a particular region can be attributed to deficiencies in OC availability or VOC oxidant concentrations. Comparisons to limited observational and modelled data suggest that the MOZART-2 SOA model provides a good representation of global averaged SOA. SOA mass concentrations, predicted by models such as MOZART-2, can be used in part to model the dynamics of an SOA population (e.g. size of particles, number concentrations etc.). Aerosol properties such as size and number concentration can then be used to estimate their effect on climate and health. The explicit representation of the processes that affect aerosol dynamics, such as nucleation, condensation, evaporation and coagulation can be complex and use significant computational resources. Simplification of the discrete coagulation equation and empirical coagulation coefficients for continuum and non-continuum regime diffusion kinetics provided a simplified method of coagulation capable of predicting the evolution of inert sodium chloride aerosol in chamber experiments. A variable coagulation coefficient (linked to the mean particle number concentration of each experiment) was developed. This method is an empirical surrogate for the standard coefficient corrections applied to Brownian based diffusion in the continuum regime to account for the different kinetic effects within the transition and free molecular diffusion regimes. This method removes the need for calculating individual coefficients for each particle interaction. Estimates of modeluncertainty show that within uncertainty limits the model provides a good representation of experimental data. Correlation and index of agreement (IOA) calculations revealed good statistical agreement between modelled and experimental. Some experiments showed degrees of coagulation under prediction using the variable coefficient technique. Investigations into the effect of aerosol type and size, temperature and humidity may be necessary to refine the variable coefficient calculation technique. The model showed little sensitivity to model time step and is capable of high resolution representation of the aerosol. Mass concentration is conserved within the model whereas some error due to numerical diffusion within the number concentrations results from the bin sectioning technique used. The simplicity of this sectioning method over other methods and the minimal effect of numerical diffusion establishes a simplified method of modelling relative to the high resolution of the aerosol distribution the model achieves. It is suggested that the efficiency improvements introduced by the approaches used in developing this model provide an efficient ultra-fine coagulation modelling for atmospheric models. A semi-empirical model for SOA dynamics (SPLAT) incorporating coagulation, nucleation, condensation and evaporation was developed. The aim of the model and the development process was to predict, with high resolution and minimal computational expense, the formation and growth of SOA given a SOA mass input as a function of time. The average size distribution profile from chamber experimental data was used as part of the nucleation module. This technique provided an alternative method of representing the particle distribution compared to those models that assume a single diameter of nucleated particle or a fixed log-normal mode for the entire evolution of SOA. All SPLAT simulations assume organic nucleation events within the experiments modelled, although it is stilluncertain whether they occur in the atmosphere. The modelled nucleation events have produced a single nucleation burst, a result of immediate domination of condensation as soon as nucleation occurs. This deficiency is likely to be a result of the assumption of free molecular diffusion for condensation. The rate of condensation, calculated at every time step, is based on the aerosol size distributed surface area and the particle-size-dependent saturation mass concentrations. The SPLAT coagulation module was a version of the model developed in Chapter 6. Comparisons between experimental and modelled data showed good agreement. These comparisons revealed the shortcomings in the nucleation module while a statistical analysis of the modelled and experimental data has shown SPLAT to be effective in modelling a range of SOA systems. The complexity introduced in modelling aerosol dynamics in high resolution is offset in SPLAT by efficiency improvements due to the insensitivity of the model to time step size and simplified methods of bin sectioning, nucleation, coagulation, condensation and evaporation. Published SOA yields can be applied to predict SOA mass at local, regional or global scales. Although previously unreported uncertainties in these yields have been shown to exist, the MOZART-2 global chemical transport model has shown that SOA mass concentration can be predicted with reasonable quality, considering the scale of the model and limited observational data. These global scale SOA mass predictions can be used purely for global burden and occurrence, or as the input for modelling the dynamics of an aerosol population, which is significant for estimating an aerosol population's effect on climate change and health. SOA mass concentrations from chamber experiments were used as input to a SOA dynamics model. This model (SPLAT) then predicted the evolution of particle number concentrations and size within these experiments based on this mass input. Application of the dynamics model to the output of the MOZART-2 model could then provide a comprehensive global scale SOA modelling package.

This dissertation is a collection of studies that investigates the issue of air pollution in the field of environmental chemistry. My thesis consists of research works done to measure the concentration of particulate matter (PM) and gas-phase species in ambient air. High concentrations of PM is a significant problem in Utah and in other regions of the world. Particles having an aerodynamic diameter of 2.5 micrometers and smaller play a crucial role in air pollution and pose serious health risks when inhaled. PM is composed of both organic and inorganic components. The organic fraction in PM ranges from 10-90% of the total particle mass. Several methods have been employed to measure the organic fraction of PM, but these techniques require extensive laboratory analysis, expensive bench top equipment, and do a poor job of capturing diurnal variations of the concentrations of ambient organic compounds. The Hansen Lab has developed a new instrument called the Organic Aerosol Monitor (OAM) which is based on gas chromatography followed by mass spectrometry detection platform for measuring the carbonaceous component of PM2.5 on an hourly averaged basis. Organic marker data collected in 2016 using the OAM was used in a Positive Matrix Factorization (PMF) analysis to identify the sources of PM in West Valley City, Utah. Additionally, data was collected in Richfield and Vernal, UT in 2017 - 2018 to quantitatively monitor the composition of organic markers of PM2.5. Some previously unidentified organic compounds in PM were successfully identified during this study, including terpenes, polycyclic aromatic hydrocarbons (PAHs), diethyl phthalate, some herbicides, and pesticides. Gas-phase species play a significant role in driving the formation of air pollutants in Earth's atmosphere. Traditional gas detection methods do not provide high temporally and spatially resolved data; therefore, it becomes important to detect and measure gas-phase species both qualitatively and quantitatively to better understand the sources of air pollution. An incoherent broadband cavity enhanced absorption spectrometer (IBBCEAS) combines a broadband incoherent light source, a stable optical cavity formed by two highly reflective mirrors and a charged-coupled device (CCD) detector to quantitatively measure the gas-phase compounds present in the atmosphere. The concentrations of formaldehyde (HCHO) were measured using IBBCEAS to investigate the sources of this hydrocarbon in Bountiful, Utah during 2019. Another important species is OH radical. It is one of the most predominant oxidizing species present in the atmosphere. It is found in low concentrations, 0.1 ppt. Detecting concentrations this low is challenging. A new IBBCEAS instrument has been designed and elements of this instrument were tested by measuring the OH overtones in a variety of short chained alcohols. A set of experiments were conducted to measure the absorption cross-sections for the 5th and 6th OH vibrational overtones in a series of short chained alcohols by IBBCEAS. Because OH radical's lowest energy electronic state occurs in the same wavelength region (i.e., 308 nm) that SO2 absorbs (300-310 nm), a study was conducted in which the concentrations of SO2 were measured using an IBBCEAS and compared with a commercially available SO2 monitor.