Understanding the interaction between atmospheric aerosol and water vapour is key in assessing the impacts of anthropogenic influences on the earth's radiative budget, both directly through scattering and absorbing incident solar radiation, and indirectly through changing cloud properties, with considerable uncertainty in the magnitude of the estimated forcings of the latter. Although aerosol particle water uptake is well defined for inorganic compounds, the effects of the aerosol organic fraction on cloud droplet formation and cloud condensation nuclei (CCN) properties are relatively poorly characterised, due to the large number of organic compounds present in atmosphere and their highly complex influences on properties such as water solubility and surface tension.This thesis presents extensive field measurements of CCN/aerosol hygroscopicity from three different environments, together with a novel error model, which has been developed to propagate instrumental uncertainties from measurements in the sub- and supersaturated regimes through to commonly used data products used in large-scale models. This study illustrates that a single hygroscopicity framework is not able to reconcile the measurements within errors, for different measurement environments. The sensitivity of this type of reconciliation study was assessed using several different scenarios, making different assumptions in each case; sensitivity tests using a 'typical' regional aerosol particle water uptake or number-size distribution, demonstrate that it is not possible to apply a constant correction to data to guarantee reconciliation, that the best reconciliation was achieved for size-resolved high-temporal water uptake and aerosol number-size distribution data, and that the application of single-parameter hygroscopicity models requires further examination. It is concluded that high-temporal size-resolved measurements of sub- and supersaturated particle water uptake are fundamental to providing a thorough characterisation of the interaction between atmospheric aerosol and water vapour, and are essential in order to achieve the best possible predictive capability from large-scale models.

Global warming theories continue to overestimate their predictions of increased mean global temperatures (Hudson 1991). This would imply that some other influence is counteracting the global warming influences; i.e. a cooling effect. Cloud albedo characteristics are currently being researched to determine the impact clouds have on the net cooling of the atmosphere in relation to the global warming theory. These characteristics are influenced by the type, size, composition, and abundance of aerosol particles that act as cloud condensation nuclei. This study employs Tandem Differential Mobility Analyzer (TDMA) data collected in the vicinity of Japan during the Asian Aerosol Characterization Experiment (ACE-Asia) to investigate the influence of aerosol concentration and composition on the light scattering properties of clouds. Measurements of particle size (Dp), particle growth factor (GF), and relative humidity (RH) yield critical supersaturations (Sc) with the assumption that the soluble part of the particle is composed primarily of one substance. This indirect composition analysis allows us to determine whether the aerosol was internally mixed (particles have uniform composition and yield a single-peak distribution or similar growth factors) or externally mixed (different particles have different compositions yielding multiple peaks in the distribution). Through the use of calculated supersaturations, we can gain insight into cloud droplet activation properties of the samples for various aerosol types, which ultimately allows us to look at the influence of these particles on albedo characteristics of clouds formed by these particles.

Soot particles released from fossil fuel combustion and biomass burning have a large impact on the regional/global climate by altering the atmospheric radiative properties and by serving as cloud condensation nuclei (CCN). However, the exact forcing is affected by the mixing of soot with other aerosol constituents, such as sulfuric acid. In this work, experimental studies have been carried out focusing on three integral parts: (1) heterogeneous uptake of sulfuric acid on soot; (2) hygroscopic growth of H2SO4-coated soot aerosols; (3) effect of H2SO4 coating on scattering and extinction properties of soot particles. A low-pressure laminar-flow reactor, coupled to ion driftchemical ionization mass spectrometry (ID-CIMS) detection, is used to study uptake coefficients of H2SO4 on combustion soot. The results suggest that uptake of H2SO4 takes place efficiently on soot particles, representing an important route to convert hydrophobic soot to hydrophilic aerosols. A tandem differential mobility analyzing (TDMA) system is employed to determine the hygroscopicity of freshly generated soot in the presence of H2SO4 coating. It is found that fresh soot particles are highly hydrophobic, while coating of H2SO4 significantly facilitates water uptake on soot even at sub-saturation relative humidities. The results indicate that aged soot particles in the atmosphere can potentially be an efficient source of CCN. Scattering and extinction coefficient measurements of the soot-H2SO4 mixed particles are conducted using a threewavelength Nephelometer and a multi-path extinction cell. Coating of H2SO4 is found to increase the single scattering albedo (SSA) of soot particles which has impact on the aerosol direct radiative effect. Other laboratory techniques such as transmission electron microscopy (TEM) and Fourier transform infrared spectrometry (FTIR) are utilized to examine the morphology and chemical composition of the soot-H2SO4 particles. This work provides critical information concerning the heterogeneous interaction of soot and sulfuric acid, and how their mixing affects the hygroscopic and optical properties of soot. The results will improve our ability to model and assess the soot direct and indirect forcing and hence enhance our understanding of the impact of anthropogenic activities on the climate.

Global warming theories continue to overestimate their predictions of increased mean global temperatures (Hudson 1991). This would imply that some other influence is counteracting the global warming influences; i.e. a cooling effect. Cloud albedo characteristics are currently being researched to determine the impact clouds have on the net cooling of the atmosphere in relation to the global warming theory. These characteristics are influenced by the type, size, composition, and abundance of aerosol particles that act as cloud condensation nuclei. This study employs Tandem Differential Mobility Analyzer (TDMA) data collected in the vicinity of Japan during the Asian Aerosol Characterization Experiment (ACE-Asia) to investigate the influence of aerosol concentration and composition on the light scattering properties of clouds. Measurements of particle size (Dp), particle growth factor (GF), and relative humidity (RH) yield critical supersaturations (Sc) with the assumption that the soluble part of the particle is composed primarily of one substance. This indirect composition analysis allows us to determine whether the aerosol was internally mixed (particles have uniform composition and yield a single-peak distribution or similar growth factors) or externally mixed (different particles have different compositions yielding multiple peaks in the distribution). Through the use of calculated supersaturations, we can gain insight into cloud droplet activation properties of the samples for various aerosol types, which ultimately allows us to look at the influence of these particles on albedo characteristics of clouds formed by these particles.

The indirect effect of atmospheric aerosol on climate remains a large source of uncertainty in anthropogenic climate change prediction. An important fraction of this uncertainty arises from the impacts of organic aerosol on cloud droplet formation. Conventional thinking says that organic aerosol hygroscopicity, typically represented by the hygroscopicity parameter κ, increases with oxidation, most commonly represented by the oxygen to carbon ratio of the aerosol, O:C. Furthermore, these quantities are expected to increase as aerosol volatility decreases. Results indicate that the link between organic aerosol hygroscopicity and oxidation is not always straightforward, and in some cases, the average carbon oxidation state OSc appears to be a better indicator of oxidation than the oxygen to carbon ratio, O:C. In chamber and ambient studies, the least volatile fraction of the aerosol also appeared to be the least hygroscopic, contradictory to current thinking; however, in both cases, thermally-denuded aerosol showed greater oxidation, in terms of OSc, than non-denuded aerosol. When these findings are placed in the context of numerous published studies from a variety of different environment, the overall trend of increasing organic hygroscopicity with O:C still holds. This is also true for volatilized aerosol, though the magnitude of organic hygroscopicity is generally lower than that of non-denuded aerosol.

We examine three case studies during the Deep Convective Clouds and Chemistry (DC3) field experiment when storm inflow and outflow air were sampled for aerosol subsaturated hygroscopicity and the real part of refractive index (n) with a Differential Aerosol Sizing and Hygroscopicity Probe (DASH-SP) on the NASA DC-8. Relative to inflow aerosol particles, outflow particles were more hygroscopic (by 0.03 based on the estimated parameter) in one of the three storms examined. Two of three control flights with no storm convection reveal higher values, albeit by only 0.02, at high altitude (> 8km) versus < 4km. Entrainment modeling shows that measured values in the outflow of the three storm flights are higher than predicted values (by 0.03-0.11) based on knowledge of values from the inflow and clear air adjacent to the storms. This suggests that other process(es) contributed to hygroscopicity enhancements such as secondary aerosol formation via aqueous-phase chemistry. Values of n were higher in the outflow of two of the three storm flights, reaching as high as 1.54. More statistically significant differences were observed in control flights (no storms) where n decreased from 1.50-1.52 (< 4km) to 1.49-1.50 (> 8km). Chemical data show that enhanced hygroscopicity was coincident with lower organic mass fractions, higher sulfate mass fractions, and higher O:C ratios of organic aerosol. Refractive index did not correlate as well with available chemical data. Deep convection is shown to alter aerosol radiative properties, which has implications for aerosol effects on climate.

A cobertura de nuvens e os aerossóis são os dois principais fatores que modulam a energia solar que atinge a superfície e é absorvida pela atmosfera. Esses dois fatores, portanto, têm um papel essencial no clima do planeta. Há atualmente um interesse nos efeitos radiativos dos aerossóis, particularmente por causa da atividade antrópica, que aumenta sua concentração na atmosfera, e por sua íntima relação com a formação de nuvens. Partículas que podem ser ativadas e ganhar água para se tornarem nevoeiro ou gotas de nuvens, na presença de supersaturação de vapor de água, são chamadas de Núcleo de Condensação de Nuvens. O estudo das partículas que aumentam de tamanho com o ganho de água conforme aumenta a umidade relativa (higroscopicidade) torna-se então de fundamental importância no entendimento da contribuição dos aerossóis na regulação do clima do planeta. O LIDAR é um instrumento promissor no estudo da higroscopicidade dos aerossóis atmosféricos, porque pode operar em ambiente não perturbado e em condições muito próximas da saturação. O LIDAR Raman apresenta a vantagem de poder obter o perfil de vapor de água e retroespalhamento de aerossóis no mesmo volume atmosférico e sem nenhuma suposição a priori a respeito da razão LIDAR Este trabalho objetiva avaliar o crescimento higroscópico do material particulado urbano em São Paulo, Brasil, e em Washington, D.C, Estados Unidos durante a campanha NASA-Discover-AQ com o uso da técnica LIDAR Raman, obtendo o fator de crescimento por higroscopicidade. Apesar da metodologia que se baseia na determinação de uma atmosfera bem misturada com o uso de radiossondagem já ter sido utilizada na literatura, este trabalho acrescenta importantes informações, já que não se tem notícias de outros estudos extensos com múltiplos casos feitos com o LIDAR Raman para avaliação de higroscopicidade nos Estados Unidos, bem como é a primeira vez que este estudo é feito em São Paulo, como resultado de três anos de aquisição de dados. Os resultados mostram que é possível identificar o crescimento higroscópico dos aerossóis em ambas os ambientes de estudo, cuja detecção depende de condições atmosféricas que estão raramente presentes, tornando o estudo da higroscopicidade com o LIDAR um desafio que exige uma extensa coleta de dados. Mostram ainda que a determinação da origem e o estudo conjugado das propriedades químicas da população de aerossóis são informações que auxiliariam no entendimento do comportamento higroscópico, aprofundamentos estes que podem ser derivados deste trabalho. / The cloud cover and aerosols are two main factors that modulate the solar energy that reaches the surface and is absorbed by the atmosphere. These two factors therefore have a key role in global climate. There is currently an interest in the radiative effects of aerosols, particularly because of human activity, increasing its concentration in the atmosphere, and its close relationship with cloud formation Particles that can be activated and gain water to form fog or cloud droplets in the presence of water vapor supersaturation, are called Cloud Condensation Nucleus. The study of particles that increase in size because of the uptake of water under increasing relative humidity conditions (hygroscopicity) then becomes of fundamental importance in understanding the contribution of aerosols in regulating the global climate. The LIDAR is a promising tool in the study of hygroscopic properties of atmospheric aerosols, because it can operate in undisturbed environment and much close to saturation conditions. The Raman LIDAR has the advantage of being able to obtain the profile of water vapor and aerosol backscatter at the same atmospheric volume and no a priori assumption of the LIDAR ratio. This study aims to evaluate the hygroscopic growth of urban particulate matter in Sao Paulo, Brazil, and Washington, DC, United States during the NASA-Discover-AQ campaign using the technique Raman LIDAR, getting the growth factor by hygroscopicity . Although the methodology - which is based on determination of a well-mixed atmosphere using radiosonde - have already been described in the literature, this work adds important information, since they do not have other news with multiple cases extensive studies made with the LIDAR Raman hygroscopicity for evaluation in the United States, and is the first time that this study is done in São Paulo, as a result of three years of data acquisition. The results show that it is possible to identify the hygroscopic growth of aerosol in both environments, whose detection depends on atmospheric conditions that are rarely present, making the study of hygroscopic properties with LIDAR a challenge that requires extensive data collection. Also, show that the determination of origin and the combined study of chemical properties of the population of aerosols would assist in the understanding of hygroscopic behavior.

A cobertura de nuvens e os aerossóis são os dois principais fatores que modulam a energia solar que atinge a superfície e é absorvida pela atmosfera. Esses dois fatores, portanto, têm um papel essencial no clima do planeta. Há atualmente um interesse nos efeitos radiativos dos aerossóis, particularmente por causa da atividade antrópica, que aumenta sua concentração na atmosfera, e por sua íntima relação com a formação de nuvens. Partículas que podem ser ativadas e ganhar água para se tornarem nevoeiro ou gotas de nuvens, na presença de supersaturação de vapor de água, são chamadas de Núcleo de Condensação de Nuvens. O estudo das partículas que aumentam de tamanho com o ganho de água conforme aumenta a umidade relativa (higroscopicidade) torna-se então de fundamental importância no entendimento da contribuição dos aerossóis na regulação do clima do planeta. O LIDAR é um instrumento promissor no estudo da higroscopicidade dos aerossóis atmosféricos, porque pode operar em ambiente não perturbado e em condições muito próximas da saturação. O LIDAR Raman apresenta a vantagem de poder obter o perfil de vapor de água e retroespalhamento de aerossóis no mesmo volume atmosférico e sem nenhuma suposição a priori a respeito da razão LIDAR Este trabalho objetiva avaliar o crescimento higroscópico do material particulado urbano em São Paulo, Brasil, e em Washington, D.C, Estados Unidos durante a campanha NASA-Discover-AQ com o uso da técnica LIDAR Raman, obtendo o fator de crescimento por higroscopicidade. Apesar da metodologia que se baseia na determinação de uma atmosfera bem misturada com o uso de radiossondagem já ter sido utilizada na literatura, este trabalho acrescenta importantes informações, já que não se tem notícias de outros estudos extensos com múltiplos casos feitos com o LIDAR Raman para avaliação de higroscopicidade nos Estados Unidos, bem como é a primeira vez que este estudo é feito em São Paulo, como resultado de três anos de aquisição de dados. Os resultados mostram que é possível identificar o crescimento higroscópico dos aerossóis em ambas os ambientes de estudo, cuja detecção depende de condições atmosféricas que estão raramente presentes, tornando o estudo da higroscopicidade com o LIDAR um desafio que exige uma extensa coleta de dados. Mostram ainda que a determinação da origem e o estudo conjugado das propriedades químicas da população de aerossóis são informações que auxiliariam no entendimento do comportamento higroscópico, aprofundamentos estes que podem ser derivados deste trabalho. / The cloud cover and aerosols are two main factors that modulate the solar energy that reaches the surface and is absorbed by the atmosphere. These two factors therefore have a key role in global climate. There is currently an interest in the radiative effects of aerosols, particularly because of human activity, increasing its concentration in the atmosphere, and its close relationship with cloud formation Particles that can be activated and gain water to form fog or cloud droplets in the presence of water vapor supersaturation, are called Cloud Condensation Nucleus. The study of particles that increase in size because of the uptake of water under increasing relative humidity conditions (hygroscopicity) then becomes of fundamental importance in understanding the contribution of aerosols in regulating the global climate. The LIDAR is a promising tool in the study of hygroscopic properties of atmospheric aerosols, because it can operate in undisturbed environment and much close to saturation conditions. The Raman LIDAR has the advantage of being able to obtain the profile of water vapor and aerosol backscatter at the same atmospheric volume and no a priori assumption of the LIDAR ratio. This study aims to evaluate the hygroscopic growth of urban particulate matter in Sao Paulo, Brazil, and Washington, DC, United States during the NASA-Discover-AQ campaign using the technique Raman LIDAR, getting the growth factor by hygroscopicity . Although the methodology - which is based on determination of a well-mixed atmosphere using radiosonde - have already been described in the literature, this work adds important information, since they do not have other news with multiple cases extensive studies made with the LIDAR Raman hygroscopicity for evaluation in the United States, and is the first time that this study is done in São Paulo, as a result of three years of data acquisition. The results show that it is possible to identify the hygroscopic growth of aerosol in both environments, whose detection depends on atmospheric conditions that are rarely present, making the study of hygroscopic properties with LIDAR a challenge that requires extensive data collection. Also, show that the determination of origin and the combined study of chemical properties of the population of aerosols would assist in the understanding of hygroscopic behavior.

Soot aerosols are well known to be atmospheric constituents, but the hydrophobic nature of fresh soot likely prohibits them from encouraging cloud development. Soot aged through contact with oxygenated organic compounds may become hydrophilic enough to promote water uptake. In this study, the tandem differential mobility analyzer (TDMA) and differential mobility analyzer?aerosol particle mass analyzer (DMA?APM) were employed to measure the changes in morphology and hygroscopicity of soot aerosol particles upon coating with succinic and glutaric acids. The effective densities, fractal dimensions and dynamic shape factors of fresh and coated soot aerosol particles have been determined. Significant size-dependent increases of soot particle mobility diameter, mass, and effective density (?eff) were observed upon coating of aggregates with succinic acid. These properties were restored back to their initial states once the acid was removed by heating, suggesting no restructuring of the soot core had occurred. Coating of soot with glutaric acid, on the other hand, leads to a strong size shrinking with a diameter growth factor ~0.60, even after the acid has been removed by heating suggesting the strong restructuring of the soot agglomerate. The additional 90% RH cycle can evidently enhance the restructuring process. The extinction and scattering properties at 532 nm of soot particles internally mixed with dicarboxylic acids were investigated experimentally using a cavity ring-down spectrometer and an integrating nephelometer, respectively, and the absorption is derived as the difference between extinction and scattering. It was found that the organic coatings significantly affect the optical and microphysical properties of the soot aggregates. The size-dependent amplification factors of light scattering were as much as 3.8 and 1.7 with glutaric and succinic acids coatings, respectively. Additional measurements with soot particles that are first coated with glutaric acid and then heated to remove the coating show that both scattering and absorption are enhanced by irreversible restructuring of soot aggregates to more compact globules. These results reveal the microphysical state of soot aerosol with incomplete restructuring in the atmosphere, and advance the treatment of atmospheric aged soot aerosol in the Mie theory shell-and-core model.

En atmosphère naturelle, l’eau est l’un des facteurs contribuant fortement à la masse des particules d’aérosol. Ceci va fortement modifier les propriétés optiques et radiatives des aérosols. Cet impact a été calculé à partir de plus de 2 ans de mesures sur le site ACTRIS/GAW du Puy de Dôme (PdD, 1565m). La distribution en taille, l’extinction et l’hygroscopicité mesurées au PdD ont été combinées pour calculer les propriétés optiques et radiatives, sèches ou humides. Pour chaque propriété, le facteur d’accroissement hygroscopique (f) a été estimé à l’aide d’un code de Mie. La longue série temporelle a permis de paramétrer l’évolution en fonction de l’humidité des propriétés optiques de différents types d’aérosols. Pour un aérosol d’origine océanique qui s’est mélangé avec des aérosols anthropiques, le coefficient de diffusion augmente plus de 4.4 fois si il est placé à 90% d’humidité. Le forçage radiatif va évoluer en conséquence et sera 2.8 fois plus élevé à 90% d’humidité que pour une atmosphère sèche (1.8 à humidité ambiante). Cette longue série de mesures a également permis de montrer, pour la première fois à notre connaissance, la forte variation saisonnière de ce paramètre. Ce manuscrit présente également une méthode originale pour calculer la masse d’aérosols volcaniques à partir de mesures LIDAR et in situ. Lors de l’éruption du volcan Islandais Eyjafjalla en Mai 2010, la masse d’aérosols volcaniques au dessus de Clermont a été estimée de 655±23μg.m-3. / Water contributes significantly to the aerosol mass under ambient conditions of relative humidities, and thus may significantly impact their optical and radiative properties and direct effect. In the present work, the impact of the aerosol hygroscopicity on its optical properties is evaluated from a set of instrumentation located at the ACTRIS/GAW Puy de Dôme station (PdD, 1465m) over two years of measurements in 2010 and 2011. In situ size distributions, extinction and hygroscopicity measurements are combined to retrieve the aerosol refractive index, both dry and wet. For each optical property the enhancement factor (f) due to hygroscopicity can be computed using Mie calculations. The long data set available enables us to generate parameterisations of optical properties enhancement as a function of relative humidities for different aerosol types. At 90% humidity, fσsca is more than 4.4 for marine aerosol that have mixed with a pollution plume. Consequently, the aerosol radiative forcing is estimated to be 2.80 times higher at RH=90% and 1.75 times higher at ambient RH when hygroscopic growth of the aerosol is considered. For the first time this study highlight the high seasonal variability of this impact. The manuscript also presents an original method of mass inversion for volcanic aerosols with the synergy of in situ and LIDAR measurements. The calculated mass of volcanic particle transported over Clermont during the eruption of Eyjafjalla in May 2010 was up to 655±23μg.m-3.