Dissertations / Theses on the topic 'Aerosols Atmospheric radiation'

Thesis (Ph.D.)--George Mason University, 2008.
Vita: p. 167. Thesis director: Menas Kafatos. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Earth Systems an GeoInformation Sciences. Title from PDF t.p. (viewed Jan. 11, 2009). Includes bibliographical references (p. 156-166). Also issued in print.

The extinction of solar radiation by atmospheric aerosols influences the Ultraviolet (UV) flux at the surface, which in turn has implications on both human and environmental health. In this study we present measurements of aerosol optical depth ( and #964;a) in the UV at Boulder, Colorado and Atlanta, Georgia using direct measurements of solar UV radiation. The wavelength dependence of and #964;a and the single scattering albedo ( and #969;o) are determined from the measured values of and #964;a. Daily averages of and #964;a range between 0.09 and 0.52 at Boulder and between 0.23 and 2.09 for Atlanta between the wavelengths of 332 and 340 nm. The average ngstrm exponent ( and #945;) is 0.83 at Boulder and 1.43 in Atlanta. Results clearly show that aerosols have a significant effect on the UV Index. Day-to-day changes in the UV index during the one month measurement period in Atlanta range between 2-3 UV Index units at solar noon. It is estimated that when changes in and #964;a and and #969;o occur simultaneously, the UV Index can change up to 6 units from one day to the next at solar noon in the Atlanta area. The single scattering albedo ( and #969;o) was estimated to range between 0.8 and 0.99 for Atlanta. The results suggest an increasing trend in and #969;o with increases in and #964;a. In addition, a new synthetic current UV Index is developed which expands to nearly 10,000 cities the number of current UV Index reports that can be distributed to the public in the United States. Right now, current UV Index values are limited to specific UV measuring sites, constrained by the difficulties of maintaining accurate calibration within the network of UV instruments. The distribution of UV Index values to more cities will increase the publics awareness of the harmful effects of the sun. This new UV Index can be accessed through The Weather Channel website.

The feedbacks among aerosols, clouds, and radiation are important components for understanding Earth's climate system and quantifying human-induced climate change, yet the magnitude of these feedbacks remain highly uncertain. Since every cloud droplet in the atmosphere begins with water condensing on a pre-existing aerosol particle, characterizing the ability of aerosols to uptake water vapor and form cloud condensation nuclei (CCN) are key to understanding the microphysics behind cloud formation, as well as assess the impact aerosols have on the Earth system. Through a combination of controlled laboratory experiments and field measurements, this thesis characterizes the ability of atmospheric aerosols to uptake water vapor and become CCN at controlled levels of water vapor supersaturation. The origin of the particle water uptake, termed hygroscopicity, is also explored, being from either the presence of deliquescent soluble material and/or adsorption onto insoluble surfaces. The data collected and presented is comprehensive and includes (1) ground samples of volcanic ash, collected from six recent eruptions re-suspended in the laboratory for analysis, (2) laboratory chamber and flow-tube studies on the oxidation and uptake of surface active organic compounds, and (3) in-situ aircraft measurements of aerosols from the Arctic background, Canadian boreal forests, fresh and aged biomass burning, anthropogenic industrial pollution, and from within tropical cyclones in the Atlantic basin. Having a more thorough understanding of aerosol water uptake will enable more accurate representation of cloud droplet number concentrations in global models, which can have important implications on reducing the uncertainty of aerosol-cloud-climate interactions, as well as additional uncertainties in aerosol transport, atmospheric lifetime, and impact on storm dynamics.

One of the most important radiative properties of aerosols is their optical thickness (AOD), which is closely linked to the total burden of atmospheric aerosols. On the contrary, we do avail of long time series of sunshine duration (SD) measurements, which is defined as the total time length of those sub-periods for which the direct solar irradiance exceeds a certain threshold. In the past, the Campbell-Stokes sunshine recorder (CSSR) has been the most common instrument for measuring SD. Specifically, SD is obtained measuring the length of the burn produced on a cardboard. The principal goal of the present thesis is to investigate the suitability of sunshine observations, as well as the width of the burn on the cards, for detecting changes in atmospheric aerosol load for both high time resolution and long time scales. The initial hypothesis is that an increase of AOD reduces both SD and the burn width.
Una de les propietats radiatives més importants dels aerosols atmosfèrics és el seu espessor òptic (AOD), que està molt vinculat a la càrrega total d’aerosols en l’atmosfera. Per altra banda, existeixen llargues series temporals d’insolació (SD), que es defineix com la suma de subperíodes en què la irradiància solar directa excedeix un cert llindar. En el passat, l’heliògraf Campbell-Stokes ha estat l’instrument més comú per la mesura de SD, obtinguda a partir de la longitud de la cremada produïda en una banda de cartolina. L’objectiu principal d’aquesta tesi ha estat investigar la idoneïtat de la utilització de mesures de SD, així com l’amplada de les cremades en les cartolines, per tal de detectar canvis en la càrrega d’aerosols atmosfèrics, tant en alta resolució temporal com en llargues escales temporals, partint de la hipòtesis de que un augment de l’AOD redueix tant la mesura de SD com l’ample de la cremada.

An investigation of the high spectral resolution signatures and radiative forcing of tropospheric aerosol in the thermal infrared was conducted. To do so and to support advanced modeling of optical properties, a high spectral resolution library of atmospheric aerosol optical constants was developed. This library includes new optical constants of sulfate-nitrate-ammonium aqueous solutions and the collection of a broad range of existing optical constants for aerosol components, particularly mineral optical constants. The mineral optical constants were used to model and study infrared dust optical signatures as a function of composition, size, shape and mixing state. In particular, spherical and non-spherical optical models of dust particles were examined and compared to high spectral resolution laboratory extinction measurements. Then the performance of some of the most common effective medium approximations for internal mixtures was examined by modeling the optical constants of the newly determined sulfate-nitrate-ammonium mixtures. The optical signature analysis was applied to airborne and satellite high spectral resolution thermal infrared radiance data impacted by Saharan dust events. A new technique to retrieve dust microphysical properties from the dust spectral signature was developed and compared to a standard technique. The microphysics retrieved from this new technique and from a standard technique were then used to investigate the effects of dust on radiative forcing and cooling rates in the thermal IR.

Orientador: Jurandir Zullo Junior
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agricola
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Resumo: O sensoriamento remoto nas regiões espectrais do visível e do infravermelho próximo constitui uma das ferramentas mais importantes para o entendimento da biosfera e de suas dinâmicas. Entretanto, estas duas regiões são afetadas pelos efeitos atmosféricos tais como, o espalhamento e a absorção,ocasionados por sua vez pelos aerossóis e gases atmosféricos. Na tentativa de obter o fator de reflectância bi-direcional da superfície terrestre, nos canais 1 e 2 do sensor AVHRR, foi realizada a correção atmosférica, baseada na entrada de dados, tais como espessura óptica dos aerossóis, coluna total de vapor d?água e carga total de ozônio, respectivamente fornecidos pelo sensor MODIS. O intuito da utilização deste sensor está diretamente relacionado à obtenção das informações, necessários para a correção atmosférica, considerando-se a variabilidade dos parâmetros no tempo e no espaço. Para tanto foi utilizado o aplicativo SCORADIS, fundamentado no modelo de transferência radiativa 5S, então adaptado, para possibilitar a correção atmosférica de toda a imagem do AVHRR a partir da entrada das imagens correspondentes aos planos atmosféricos, através da utilização de quatro metodologias distintas de correção atmosférica. As análises realizadas indicaram que as correções realizadas a partir dos dados atmosféricos do sensor MODIS apresentaram resultados coerentes com o esperado após a eliminação dos efeitos de espalhamento e de absorção atmosférica, nos canais 1 e 2 do NOAA-17, nas duas datas consideradas (14/07/2004 e 30/08/2005). Para o NDVI, a diferença percentual entre as imagens com e sem correção chegaram a ser de, aproximadamente, 60%, o que ressalta a importância da correção atmosférica destes canais, principalmente no acompanhamento da vegetação a partir de imagens multitemporais. Não se observou diferença significativa entre as metodologias utilizadas para a entrada dos dados atmosféricos no sistema de correção atmosférica, devido, possivelmente, à magnitude dos valores utilizados e à áreateste escolhida. Os produtos obtidos a partir das imagens do MODIS mostraram potencial para utilização na estimativa dos principais parâmetros atmosféricos necessários para a correção atmosférica (como a espessura óptica dos aerossóis e conteúdo de vapor d'água e ozônio) e que são de grande dificuldade para obtenção em campo
Abstract: Remote sensing in the spectral regions of visible and infrared is one of the most important techniques used for studying the biosphere. However these two spectral regions are affected by atmospheric effects as scattering and absorption, caused by aerosols and atmospheric gases. In the attempt to obtain the real reflectance of ground surface, in channels 1 and 2 of AVHRR sensor, was performed the atmospheric correction of two NOAA images acquired on July/14/2004 and August/30/2005, based on atmospheric data supplied by the MODIS sensor, considering the spatial and temporal variability of these parameters. The system SCORADIS, based on the radiative transfer model called 5S, was adapted to read images having values of aerosols optical thickness, water vapor content and ozone contents corresponding spatially to each pixel of a AVHRR/NOAA image. Four distinct methodologies were used to define the images of atmospheric parameters. Coherent results were obtained using atmospheric data from MODIS, indicating that the scattering and absorption effects were correctly eliminated from the NOAA images in the two dates considered. The difference between the NDVI calculated with corrected and noncorrected images was up to 60%, showing the importance of using corrected images in applications based on multitemporal images. There was not observed significant difference among the four methodologies applied to define the atmospheric data used in the atmospheric correction system due, maybe, to the magnitude of the values and to the atmospheric conditions of test-area. The atmospheric products from MODIS can be used to defining the input data (like aerosol optical thickness, water vapor contents and ozone contents) for the atmospheric correction systems of AVHRR/NOAA images
Mestrado
Planejamento e Desenvolvimento Rural Sustentável
Mestre em Engenharia Agrícola

Tropospheric aerosol information from NASA satellites in space has reached the milestone of ten years of continuous measurements. These higher resolution satellite aerosol records allow for a broader regional perspective than can be gained using only sparsely located ground based monitoring sites. Decadal satellite aerosol data have the potential to advance knowledge of the climatic impacts of aerosols through better understanding of solar dimming/brightening and radiative forcings on regional scales, as well as aid in air quality applications. The goal of this thesis is to develop and implement methodologies for using satellite remotely sensed data in conjunction with ground based observations and modeling for characterization of regional aerosol variations with applications to air quality and climate studies in the Southeastern U. S. This region is of special interest because of distinct aerosol types, less warming climate trends compared to the rest of U.S., and growing population. To support this primary goal, a technique is developed that exploits the statistical relationship between PM2.5 (particulate matter that has an aerodynamic radius of 2.5 µm or less) and satellite AOD (Aerosol Optical Depth) from MODIS (Moderate resolution Imaging Spectroradiometer) where a probabilistic approach is used for air quality assessments in the metropolitan Atlanta area. The metropolitan Atlanta area experiences the poorest air quality during the warmer seasons. We found that satellite AODs capture a significant portion of PM2.5 concentration variability during the warmer months of the year with correlation values above 0.5 for a majority of co-located (in time and space) ground based PM2.5 monitors, which is significant at the 95% confidence interval. The developed probabilistic approach uses five years of satellite AOD, PM2.5 and their related AQI (Air Quality Index) to predict future AQI based solely on AOD retrievals through the use of AOD thresholds, e.g., 80% of Code Green AQI days have AOD below 0.3. This approach has broad applicability for concerned stakeholders in that it allows for quick dissemination of pertinent air quality data in near-real time around a satellite overpass. Examination of the use of multiple satellite sensors to aid in investigating the impacts of biomass burning in the region is performed. The utility of data fusion is evaluated in understanding the effects of the large wildfire that burned in May 2007. This wildfire caused PM2.5 in the metropolitan Atlanta area to exceed healthy levels with some measurements surpassing 150 µg/m3 during the month. OMI (Ozone Monitoring Instrument) AI (Aerosol Index), which qualitatively measures absorbing aerosols, have high values of more than 1.5 during May 26 - 31, 2007. CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) a space based lidar was used to determine the vertical structure of the atmosphere across the region during the active fire period. CALIPSO was able to identify wildfire aerosols both within the planetary boundary layer (likely affects local air quality) and aloft where aerosol transport occurs. This has important implications for climatic studies specifically aerosol radiative effects. In-depth analysis of the satellite and ground based aerosol data records over the past decade (2000 - 2009) are performed from a climatic perspective. The long temporal scale allowed for better characterization of seasonality, interannual variability, and trends. Spatial analysis of ten years of AOD from both MODIS and MISR (Multi-angle Imaging Spectroradiometer) showed little variability of AOD during the winter with mean AOD below 0.1 for the entire region, while the summer had decidedly more variability with mean AOD around 0.33 for MODIS and 0.3 for MISR. Seasonal analysis of the PM2.5 revealed that summer means are twice as high as winter means for PM2.5. All of the datasets show interannual variability that suggests with time AOD and PM2.5 are decreasing, but seasonal variability obscured the detection of any appreciable trends in AOD; however, once the seasonal influence was removed through the creation of monthly anomalies there were decreasing trends in AOD, but only MODIS had a trend of -0.00434 (per month) that statistically significant at the 95% confidence level. Satellite and ground-based data are used to assess the radiative impacts of aerosols in the region. The regional TOA (Top Of the Atmosphere) direct radiative forcing is estimated by utilizing satellite AOD from MODIS and MISR both on Terra, along with satellite derived cloud fraction, surface albedo (both from MODIS), and single scattering albedo (SSA) from MISR data from 2000 - 2009. Estimated TOA forcing varied from between -6 to -3 W/m2 during the winter, and during the warmer months there is more variation with ΔF varying between -28 to -12.6 W/m2 for MODIS and -26 to -11 W/m2 for MISR. The results suggest that when AOD, cloud fraction and surface albedo are all consider they add an additional 6 W/m2 of TOA forcing compared to TOA forcing due to aerosol effects only. Varying SSA can create changes in TOA forcing of about 5 W/m2. With removal of the seasonal variability timeseries anomaly trend analysis revealed that estimated TOA forcing is decreasing (becoming less negative) with MODIS based estimates statistically significant at the 95% confidence level. Optical and radiative 1-D radiative transfer modeling is performed to assess the daily mean TOA forcing and forcing at the surface for representative urban and background aerosol mixtures for summer and winter. During the winter, modeled TOA forcing is -2.8 and -5 W/m2 for the WB and WU cases, and the modeled summer TOA forcings (SB = -13.3 W/m2) also generally agree with earlier estimates. While surface forcings varied from -3 to -210 W/m2. The radiative forcing efficiency at the TOA (amount of forcing per unit of AOD at 550 nm) varied from -9 to -72 W/m2 τ-1, and RFE at the surface varied from -50 to -410 W/m2 τ-1. It was found that the forcing efficiency for biomass burning aerosols are similar to the forcing efficiency of background aerosols during the summer that highlights the importance of possible increased biomass burning activity. Ultimately, the methodologies developed in this work can be implemented by the remote sensing community and have direct applicability for society as a whole.

Le travail presente est centre sur la situation ou l'effet radiatif des aerosols modifie la structure de la couche limite atmospherique. Trois situations sont etudiees: le cas des brumes seches, le cas des aerosols urbains et la cas du brouillard. La simulation numerique et l'approche experimentale conduisent au developpement ou la mise au point de programmes de calcul du transfert radiatif

Medidas simultâneas dos sensores CERES (Clouds and the Earths radiant Energy System) e MODIS (Moderate Resolution Imaging Spectrometer), a bordo do satélite Terra, da NASA foram utilizadas para avaliar o impacto do desflorestamento no balanço radiativo em larga escala na Amazônia durante as estações secas de 2000 a 2009. Este impacto é decorrente da emissão de partículas de queimadas, mudanças nas características de superfície e na quantidade de vapor dágua na coluna atmosférica. A forçante radiativa direta de aerossóis de queimadas e a forçante radiativa de mudança de albedo de superfície, devida ao desflorestamento na Amazônia, foram calculadas a partir de duas diferentes metodologias. O primeiro método calcula a média da forçante para toda a estação seca, através da regressão da irradiância no topo da atmosfera (TOA) versus a profundidade óptica de aerossóis. O segundo método calcula a forçante diária a partir das irradiâncias medidas no TOA e da geometria de iluminação. Um código de transferência radiativa, em conjunto com o produto de funções de distribuição de refletância bidirecional (BRDF) do MODIS e medidas de propriedades ópticas de aerossóis de queimadas da rede AERONET, foram utilizados para expandir as forçantes radiativas instantâneas, calculadas no horário de passagem do satélite, em médias diárias. A média diária da forçante radiativa direta no TOA para o período estudado, foi de - 8,2 ± 2,1 W/m² e -5,2 ± 2,6 W/m², dependendo da metodologia utilizada. As distribuições espaciais da forçante radiativa direta de aerossóis sobre a região amazônica mostram que, para altas concentrações de aerossóis, a média diária da forçante radiativa no TOA pode alcançar até -30 W/m². Observamos também que a refletância da superfície influencia fortemente o efeito radiativo direto de aerossóis. O impacto dos aerossóis sobre diferentes tipos de superfície foi analisado, indicando que a forçante radiativa é sistematicamente mais negativa sobre floresta do que sobre cerrado. A média anual da forçante radiativa de mudança de albedo de superfície devida ao desflorestamento em Rondônia foi determinada, a partir das duas diferentes metodologias, em -7,4 ± 0,9 W/m² e -8,1 ± 1,0 W/m², respectivamente. As partículas de queimadas impactam o balanço radiativo por aproximadamente 2 a 3 meses por ano, enquanto o impacto do albedo de superfície pode ser observado ao longo de todo o ano. Esta diferença, devida à sazonalidade da estação de queimadas, indica que a média anual do impacto da mudança de albedo de superfície sobre o balanço radiativo amazônico é muito maior do que o impacto anual dos aerossóis de queimadas. A influência do desmatamento na quantidade de vapor dágua atmosférico e seu impacto no balanço radiativo foi analisada a partir de medidas de vapor dágua integrado na coluna atmosférica obtidas pelos radiômetros solares da AERONET. Estas medidas mostram que a quantidade de vapor dágua integrado na coluna atmosférica é 0,35 cm (cerca de 10% do total) menor sobre áreas desmatadas do que sobre áreas de florestas preservadas. O efeito desta redução na quantidade de vapor dágua atmosférico contribui para aumentar o fluxo radiativo de ondas curtas ascendente no TOA. Os altos valores de forçante obtidos neste trabalho indicam que o desflorestamento pode ter forte implicação para a convecção, desenvolvimento de nuvens e para a razão entre radiação direta e difusa.
Simultaneous CERES (Clouds and the Earth\'s Radiant Energy System) and MODIS (Moderate Resolution Imaging Spectrometer) sensors retrievals were used to calculate the changes in radiation fluxes resulting from deforestation in the Amazon during the peak of the biomass burning seasons from 2000 to 2009. The energy balance of the region is modified by the emission of biomass burning aerosols, changes in surface properties and in the atmospheric water vapor column. The direct radiative forcing (RF) of biomass burning aerosols and the RF due to surface albedo changes, triggered by deforestation in the Amazonia, were calculated using two different methodologies. The first method calculates the average forcing for the whole dry season using a regression of fluxes in the top of the atmosphere (TOA) versus the aerosol optical depth. The second method calculates the daily forcing from the irradiances at the TOA and the illumination geometry. MODIS\'s bidirectional reflectance distribution functions (BRDF) product and biomass burning aerosol properties retrieved by AERONET were used in a radiative transfer code, to expand the instantaneous radiative forcing values, obtained during the satellite overpass, into 24-hour RF average. The mean direct RF of aerosols at the TOA during the biomass burning season for the 10-year period was -8.2 ± 2.1 W/m² and -5.2 ± 2.6 W/m², depending on the two methodologies applied. The spatial distributions of the direct radiative forcing of aerosols over the Amazon Basin show that for high concentrations of aerosols, the daily average of the RF at the TOA can reach up to -30 W/m². The surface reflectance strongly influences the direct RF of aerosols. The impact of aerosols over different surface types was analyzed, indicating that the RF is systematically more negative over forest than over cerrado areas. The mean annual land use change RF, due to deforestation, in Rondonia was determined as -7.4 ± 0.9 W/m² and -8.1 ± 1.0 W/m², using the two different methodologies. Biomass burning aerosols impact the radiative budget for approximately 2-3 months per year, whereas the surface albedo impact is observed throughout the year. Because of this difference, the estimated impact in the Amazonian annual radiative budget due to surface albedo change is much higher than the annual impact due to aerosol emissions. The influence of deforestation in the atmospheric water vapor content, and its impact in the radiative budget, was assessed using water vapor column measurements obtained by AERONET sunphotometers. It was observed that the column water vapor is on average smaller by about 0.35 cm (around 10% of the total column water vapor) over deforested areas compared to forested areas. The effect of reducing atmospheric water vapor column contributes to an increase in the upward shortwave radiative flux at the TOA. The large radiative forcing values obtained in this work indicate that deforestation have strong implications on convection, cloud development and the ratio of direct and diffuse radiation, which impacts the carbon uptake by the forest, therefore, changing the photosynthetic rate.

Suite à la signature du Protocole de Montréal en 1987, la concentration atmosphérique des substances destructrices d’ozone (ODS) est en baisse. La couche d’ozone montre des signes de récupération (Morgenstern et al. 2008a). Toutefois, l’émission des gaz à effet de serre (GHG) est en augmentation et devrait affecter au cours du 21ème siècle la distribution et les niveaux d’ozone dans l’atmosphère terrestre. En particulier, la modélisation du climat futur montre des signes d’accélération de la circulation de Brewer-Dobson transportant l’ozone de l’équateur vers les pôles. L’ozone est un constituant chimique important de l’atmosphère. Bien que nocif dans la troposphère, il est essentiel à la vie sur Terre grâce à sa capacité d’absorption d’une grande partie du rayonnement ultraviolet (UV) provenant du Soleil. Des modifications dans sa variabilité temporelle ou géographique impliqueraient des changements d’intensité du rayonnement UV à la surface de la Terre (Hegglin et al. (2009), Bais et al. (2011)). Le rayonnement UV à la surface affecte toute la biosphère. Les interactions entre rayonnement UV et écosystèmes terrestres et aquatiques sont nombreuses. Ces interactions ont des effets sur les cycles biogéochimiques et engendrent des rétroactions positives et négatives sur le climat (Erickson III et al., 2015a). La capture du CO2 atmosphérique par photosynthèse des plantes terrestres en est un exemple (Zepp et al., 2007a). Dans l’océan la pompe biologique du CO2 par la photosynthèse du phytoplancton est aussi directement affecté par la variabilité du rayonnement UV (Hader et al., 2007a). Pour l’homme le rayonnement UV est nécessaire car il participe à la photosynthèse de la vitamine D (Holick et al., 1980), mais une surexposition à des niveaux d’intensité élevés du rayonnement UV est la cause principale du développement de cancer de la peau (Matsumura and Ananthaswamy, 2004). L’objectif de ce travail de thèse est d’analyser l’évolution possible du rayonnement UV au cours du 21ème siècle, en particulier aux tropiques sud, dans le cadre des modifications climatiques attendues. Une première partie de ce travail consiste à modéliser le rayonnement UV en ciel clair dans les tropiques grâce au modèle TUV (Madronich et al., 1998) et à comparer les résultats aux mesures sols réalisées à la Réunion. Cette première partie permet l’utilisation future du modèle aux tropiques avec un bon niveau de confiance. La sensibilité du modèle de transfert radiatif en fonction de différents paramètres d’entrée est analysée (section efficace d’absorption de l’ozone,spectre extraterrestriel du soleil, ...). Les sorties du modèle sont ensuite validées à partir de mesures UV spectral au sol obtenues grâce à un spectromètre BENTHAM DM300n. Un filtrage ciel-clair des données au sol est opéré à partir de mesures de flux et de l’algorithme de Long and Ackerman (2000). Les projections climatiques des indices UV (Mc Kinlay and Diffey, 1987) sont réalisées par la suite. Pour cela, on utilise les sorties de plusieurs modèles de Chimie-Climat participant à l’exercice d’inter-comparaison CCMI (Chemistry Climate Model Initiative), couplées aux modèle TUV, validé en première partie dans les tropiques. L’exercice CCMI consiste à projeter le climat et la chimie Terrestre jusqu’en 2100 selon différents scénarios. Ces sorties décrivant la chimie et physique de l’atmosphère servent d’entrée au modèle de transfert radiatif, on obtient alors le rayonnement UV jusqu’en 2100 pour différents scénarios. Une première analyse comparative de l’UV obtenue pour quatre scénarios d’émissions (RCP2.6/4./6.0/8.5, Meinshausen et al., 2011) est effectuée. La fin du travail consiste à étudier l’impact des ODS, GHG et aérosols sur l’évolution du rayonnement UV au cours du 21ème siècle, avec un focus particulier sur les tropiques de l’hémisphère sud
Following the 1987 Montreal Protocol, atmospheric concentrations of ozone-depleting substances are decreasing. The ozone layer shows signs of recovery. Nonetheless, greenhouse gases emissions (GHG) are rising et should affect the ozone distribution in the atmosphere. Ozone is an important due to his ability to absorb ultraviolet (UV) radiation. The goal of this work is to analyse the possible evolution of UV radiation through the 21st century, particularly in the tropics, for possible climate modification. The first part of this work is to UV in clear-sky in the tropics with the TUV (Madronich et al., 1998) model and to compare against ground-based observations made on Reunion Island. This validation allows the utilisation of TUV in the tropics with a good confidence level. The sensitivity of the model is analysed for multiple parameters. Modelling output is validated against spectral ground-based measurement. Climate Projection of UVI (Mc Kinlay and Diffey, 1987) are then realized with the use of output from model participating in the CCMI ( Model Initiative) exercise and the TUV model. CCMI output describes the chemistry and physics of the atmosphere through the 21st century for four climate scenarios (RCP2.6/4.5/6.0/8.5), they are used as input for the TUV model in order to obtain UV radiation. ODS, GHG and aerosols impact on UVI evolution is analysed

In this thesis an assessment of the parameterization of the Aerosol-Radiation Interaction (ARI) in online integrated meteorology-chemistry models has been conducted. The model estimates of ARI radiative effects are still affected by significant uncertainty, mainly caused by a poor constraining of aerosol optical and microphysical properties. Hence, we firstly carried out two sensitivity studies of aerosol optical properties and ARI radiative effects to reference particle microphysical properties assumed in our online integrated meteorology-chemistry model: the NMMB-MONARCH. In the first study, perturbed assumptions on size distribution, refractive index, mass density (±20%) and shape (spheroids) have been considered for mineral dust, organic carbon and sulfate, in order to generate variability in values and spectral dependence of mass scattering cross sections (simulated with T-matrix code) in the visible range. Size distribution and refractive index have been found to have the most important impacts on aerosol scattering properties in most cases. Some constraints on the aerosol microphysical parameters have also been found through a comparison with measurements of aerosol scattering properties provided by the Institute of Environmental Assessment and Water Research (IDAEA-CSIC). Lower values of effective radius have been found more suitable for all the analyzed species and also a higher real refractive index for sulfate, with respect to reference assumptions. In the second study, size distribution and refractive index of mineral dust and organic carbon have been perturbed similarly to the first study and also two mixing states (internal and external) for a black carbon-sulfate mixture have been considered. The impacts of these perturbations on optical properties (optical depth, single scattering albedo and asymmetry factor: T-matrix code) and ARI radiative effects (simulated with RRTMG: radiative transfer model implemented in the NMMB-MONARCH) in the shortwave region have been analyzed. Different impacts on the optical properties have been found for mineral dust and organic carbon (different mean size species), while an enhanced absorption has been observed for the internal mixing between black carbon and sulfate. The absolute variations of the ARI radiative effects have been found notable, especially in extreme aerosol events. However, their relative variations with respect to base radiative fluxes have been found always lower than the perturbation range applied to the main particle microphysical properties. The full online coupling between aerosol module and radiation scheme in the NMMB-MONARCH has been implemented and also evaluated through the analysis of the model intensive optical properties (single scattering albedo and asymmetry factor). Global aerosol simulations for a 5-years period (2012-2016) have been run with the NMMB-MONARCH with activating the online coupling for all the species (reference particle microphysics: mainly OPAC). Inversion data from the Aerosol Robotic Network (AERONET: Version 2.0) from 59 stations have been used for the comparison. Also a perturbed case has been defined by assigning new refractive indexes (taken from recent literature) to almost all the species. In general the model has been found to subestimate the observed single scattering albedo and to overestimate the asymmetry factor in most stations. These observed main biases have been partially corrected by introducing the new refractive indexes: lower imaginary parts for mineral dust, primary organic matter (POM: urban/industry) and secondary organic aerosol (SOA: biogenic sources), and a higher real part for sulfate (in agreement with our first study). Possible errors in the simulation of specific species (too high dust coarse fractions, too high black carbon concentrations and lack of small and scattering particles) have been identified as possible important contributors to the observed mean biases.
En la presente Tesis doctoral se ha realizado un análisis de la parametrización de la interacción Aerosol-Radiación (IAR) en modelos meteorológico-químicos integrados on-line, a travez de dos estudios de sensibilidad y una evaluación de las propiedades ópticas de aerosoles en nuestro modelo meteorológico-químico integrado on-line: NMMB-MONARCH. En el primer estudio, se han considerado las perturbaciones en la distribución de tamaños de partículas, índice de refracción, densidad de masa (±20%) y forma (esferoides) para el polvo mineral, el carbono orgánico y el sulfato, para generar variabilidad en las eficiencias de dispersión (simuladas con un código T-matrix) en el rango visible. La distribución de tamaños y el índice de refracción han sido los parámetros con más impacto en las propiedades de dispersión de la radiación. También se ha reducido la incertidumbre de algunas propiedades al comparar con medidas experimentales de propiedades de dispersión de los aerosoles proporcionadas por el Instituto de Diagnóstico Ambiental y Estudios del Agua (IDAEA-CSIC). Valores de radio efectivo menores para todas las especies analizadas, y también una parte real del índice de refracción más elevada para el sulfato han resultado más adecuados respecto a las suposiciones iniciales. En el segundo estudio, la distribución de tamaños de partículas y el índice de refracción del polvo mineral y el carbono orgánico se han perturbado de forma similar al primer estudio, y también se han considerado dos estados de mezcla (interna y externa) para una mezcla de carbono negro y sulfato. Se ha analizado el impacto de estas perturbaciones en las propiedades ópticas (espesor óptico, albedo de dispersión simple y factor de asimetría: código T-matrix) y los efectos radiativos del IAR (simulados con el código RRTMG) en la región de longitudes de onda corta. De ello, se han identificado distintos impactos en la propiedades ópticas para el polvo mineral y el carbono orgánico, mientras que un aumento de la absorción se ha observado para las mezclas internas de carbono negro y sulfato. Las variaciones absolutas de los efectos radiativos del IAR han sido notables, especialmente en eventos intensos de aerosoles. Sin embargo, las variaciones relativas respecto a los flujos radiativos de base han sido siempre menores que el rango de perturbación aplicado a las propiedades microfísicas de las partículas. Finalmente, se ha implementado la interacción on-line entre el módulo de aerosoles y el esquema radiativo del modelo NMMB-MONARCH, y se han evaluado las propiedades ópticas intensivas del modelo (albedo de dispersión simple y factor de asimetría). Se han realizado simulaciones globales de aerosoles para un periodo de 5 años (2012-2016) con el NMMB-MONARCH activando el acoplamiento on-line para todas las componentes de aerosoles (valores de referencia para las propiedades microfísicas de los aerosoles derivados de OPAC). Datos de la red Aerosol Robotic Network (AERONET: Version 2.0) de 59 estaciones se han empleado para evaluar el modelo. También, se ha introducido una configuración perturbada asignando nuevos valores de índice de refracción (derivado de la literatura científica reciente) para la mayoría de componentes de aerosoles del modelo. En términos generales, el modelo subestima el albedo de dispersión simple observado y sobrestima el factor de asimetría en la mayoría de estaciones. Estos errores sistemáticos identificados se han corregido parcialmente al introducir la configuración perturbada: una parte imaginaria menor del índice de refracción para el polvo mineral, el aerosol orgánico primario y secundario, además de una parte real mayor para el sulfato. Los posibles errores en la simulación de componentes específicas de aerosoles (fracciones gruesas de polvo mineral demasiado elevadas, concentraciones de carbono negro demasiado elevadas y falta de partículas finas de dispersión) han sido identificados como posibles causantes de los errores identificados

Foram analisadas as principais propriedades ópticas do aerossol atmosférico a partir dos radiômetros da rede NASA/AERONET em três regiões de interesse: o Norte da Amazônia, a região do arco do desflorestamento, e a região do cerrado. A metodologia envolveu a obtenção da espessura óptica do aerossol (), distribuição de tamanho, albedo de espalhamento único (0), e outras propriedades com o uso de radiômetros CIMEL operados pela rede de fotômetros NASA/AERONET. Foram determinadas propriedades ópticas de aerossóis biogênicos naturais, bem como das emissões de queimadas. Observaram-se profundas modificações nas propriedades do aerossol durante a estação seca, como decorrência de emissões de queimadas. A profundidade óptica do aerossol, 500nm, aumentou de um valor de background de 0,15±0,13 durante a estação chuvosa, para valores médios diários da ordem de 2,5 a 3,5, o que indica uma atmosfera extremamente carregada de aerossóis na região do arco do desflorestamento. O coeficiente de Ångström, que expressa o tamanho das partículas, aumentou significativamente durante a estação de queimadas para altos valores de , indicando a predominância de partículas finas nessa época do ano, aumento esse que também é visto no volume da moda fina da distribuição de tamanho na região do arco do desflorestamento, com um pico no raio de 0,15 m. O aerossol biogênico natural está presente durante todo o ano, em todos os locais analisados. da região Amazônica. O aerossol produzido secundariamente na atmosfera, pela oxidação de compostos emitidos pela vegetação, contribui para o volume da moda fina, enquanto que as partículas primárias emitidas pela floresta contribuem para a moda grossa. Das propriedades intrínsecas do aerossol, observou-se que o albedo de espalhamento único do aerossol (0) tem valor médio de 0,920,03 nas estações do arco do desflorestamento. Em Cuiabá foi possível observar duas modas de valores de 0, uma correspondente ao aerossol natural do cerrado com valor de 0,84±0,05, e outra correspondente a queimadas de longa distância com valor de 0,92±0,03, compatível com as estações do arco do desflorestamento. O Norte da Amazônia foi caracterizado por aerossol extremamente espalhador, com albedo de 0,98±0,01 durante a estação chuvosa em Balbina. O impacto climático dos aerossóis foi quantificado através das inversões de forçante radiativa direta do aerossol da AERONET. A forçante radiativa instantânea no topo da atmosfera chegou a -100 W.m-2 na região do arco de desflorestamento. O valor de eficiência de forçante do aerossol na Amazônia variou entre 38,6 W.m-2.-1, em Alta Floresta, a 50,9 W.m-2.-1 em Belterra. Foi também realizada uma análise entre as medidas integradas na coluna atmosférica com medidas de concentração de aerossóis ao nível do solo. Nesse intuito, estudou-se a relação da profundidade óptica do aerossol obtida pelos radiômetros da AERONET e a concentração de material particulado fino, MP2,5 obtida ao nível do solo. A regressão linear encontrada foi de MP2,5 = (37±2)500 + (5±2) em unidades de [g.m-3] para a região do arco do desflorestamento, e MP2,5 = (30,7±1,3)500 + (0,08±0,40) nas mesmas unidades, para a região de Belterra. A validação feita com obtido independentemente pelo sensor MODIS mostrou que a relação é adequada para o arco do desflorestamento e a profundidade óptica do aerossol obtida por ambos os métodos pode ser usada alternativamente para estudos de efeitos de material particulado na saúde humana.
This work has analyzed the main optical properties of atmospheric aerosol particles in three regions of interest: the Northern Amazon region, the arc of deforestation and the Brazilian cerrado. The methodology involved the measurement of aerosol optical thickness (), size distribution, single scattering albedo (0), and other properties with the use of CIMEL radiometers that are part of a sun-photometer network operated by AERONET/NASA. It was determined the optical properties of natural biogenic aerosols as well as emissions from biomass burning. We observed large changes in the physical properties of aerosols during the dry season, as a result of emissions from fires. The aerosol optical depth at 500nm, 500nm increased from a background value of 0.15 ± 0.13 during the wet season for the daily average values of 2.5 to 3.5, indicating a highly loaded atmosphere in the region of the arc of deforestation. The Ångström coefficient, which indicates the particle size, increased significantly during the burning season for high values of , indicating the predominance of fine particles in this season. This increase due to biomass burning is also observed in the volume size distribution, with a large peak centered at a radius of 0.15 m. The natural biogenic aerosol is present throughout the year in all locations studied in the Amazon region with similar properties. The secondary organic aerosol produced in the atmosphere by oxidation of compounds emitted by the vegetation contributes to the volume of fine mode, while the primary particles emitted by the forest contribute to the coarse mode. The intrinsic properties of the aerosol were also analyzed. It was observed that the single scattering albedo of the aerosol (0) has an average value of 0.92 0.03 in the stations close to the region of the arc of deforestation. In Cuiabá it was possible to observe two modes in the distribution of 0, corresponding to a natural aerosol from the cerrado with an average value of 0.84 ± 0.05, and other mode corresponding to fires from long range transport with a relatively high value of 0.92 ± 0.03, consistent with the measurements at the arc of deforestation. The northern Amazon region was characterized by extremely scattering aerosols with albedo of 0.98 ± 0.01 during the rainy season in Balbina. The climate impact of aerosols was characterized by aerosol direct radiative forcing from inversions calculations by AERONET. The instantaneous radiative forcing at the top of the atmosphere reached a very high -100 Wm-2 in the region of the arc of deforestation. The value of the aerosol forcing efficiency in the Amazon ranged from -38.6 Wm-2.-1 in Alta Floresta, to -50.9 Wm-2.-1 in Belterra, compatible with measurements using other methods. This work also has done an analysis of the comparison between 500nm column measurements from AERONET and ground based aerosol concentrations. It was studied in detail the relationship of the aerosol optical depth obtained by the AERONET radiometers with the concentration of fine particulate matter, PM2.5 obtained at ground level in several sites in Amazonia. We found a statistically significant correlation and it was derived a linear regression of PM2.5 = (37±2) AOD500 + (5±2) in g/m³ in the region of the deforestation arc calculated from data in the period of 2001-2006. In addition, estimates from MODIS aerosol optical depth was used to calculate ground based PM2.5 concentrations, with statistically significant agreement. This technique is very useful to assess health effects of aerosols in Amazonia.

Thesis: Ph. D. in Environmental Chemistry, Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 125-141).
Atmospheric aerosols are important due to their adverse effects on human health and their direct and indirect radiative effects on climate, which are significant and very uncertain factors contributing to global climate change. In estimating the direct radiative effect (DRE), the absorption from carbonaceous aerosols, including black carbon (BC) and brown carbon (BrC, a component of organic aerosol, OA), are highly uncertain. This thesis addresses this uncertainty by combining models and observations to better constrain the optical properties and radiative impact of carbonaceous aerosols. First, a global model simulation (GEOS-Chem) of BC is expanded to separately treat both the aging and physical properties of BC from different sources. By combining model and observations, the global BC lifetime is found to be overestimated in previous investigations, leading to higher estimates of its warming potential. The DRE of BC is estimated to be less than one quarter of the previously reported value. Second, a new method is developed to derive BrC absorption from measurements and used to identify BrC from total absorption observations. The absorption efficiency of BrC is found to be positively correlated with the emitted BC/OA mass ratio, which is related to combustion conditions. In addition, measured BrC absorption from biomass burning plumes is found to decrease with photochemical aging with a lifetime of one day. Third, a global model simulation of BrC is developed and tested against BrC absorption measurements from aircraft campaigns in the continental United States. The BrC absorption properties from biomass burning estimated based on laboratory measurements are found to overestimate the direct measurements of ambient BrC absorption. In addition, applying a photochemical aging scheme for BrC improves the model skill. The simulation suggests that the DRE of BrC has been overestimated previously due to the lack of observational constraints from direct measurements and omission of the effects of photochemical aging. Finally, the influence of mixing state on the global absorption of carbonaceous aerosols is estimated through simplified model experiments. This thesis suggests that policies for reducing emissions of carbonaceous aerosols may have a limited impact on mitigating global climate warming.
by Xuan Wang.
Ph. D. in Environmental Chemistry

The amplitude and spectral shape of shortwave radiation are used to retrieve aerosol and cloud properties from airborne and ground based measurements. By interacting with clouds and aerosols in the Earth's atmosphere, the wavelength-dependent radiation emitted by the sun is modified. This thesis presents the change in radiation due to absorption and scattering by clouds and aerosols, which result in distinct spectral signatures in shortwave radiation spectra.

The spectral signature in shortwave radiation due to aerosols is quantified by airborne measurements of irradiance above and below aerosol layers. This radiative effect is quantified by the relative forcing efficiency, which is used to compare the impact of aerosols from different air masses, locations, and time of day. The relative forcing efficiency is the net irradiance change due to the presence of aerosols normalized by aerosol optical thickness and incident irradiance. It is shown to vary by less than 20% per unit of midvisible aerosol optical thickness for aerosols sampled during 4 different experiments, except for highly absorbing aerosols near Mexico City. The similarity in relative forcing efficiency for these experiments, not expected a priori, suggests that this quantity is constrained for various types of aerosols with differing scattering and absorption characteristics even when surface albedo differs. To estimate the radiative effect of aerosols sampled in the Los Angeles basin during one of the experiments, where no concurrent measurements of optical thickness with spectral irradiance were available, a new iterative technique was devised to use aerosol optical thickness measurements from another airborne platform.

Cloud-transmitted zenith radiance spectra were measured from the ground in Boulder, Colorado. In these measurements, spectral signatures of cloud optical and microphysical properties were uncovered. The spectral signatures are the result of radiation that is transmitted through clouds, where ice or liquid water cloud particles modulate the radiation by absorbing and scattering incident light in a wavelength-dependent manner. Typically, the magnitudes of radiance at 2 wavelengths have been used to retrieve cloud properties, but by using wavelength-dependent features more sensitivity to cloud microphysical properties is obtained. This thesis presents a method to analyze wavelength-dependent signal, where spectral features such as slopes, curvatures, and shifts in locations of maxima and minima are parameterized. These spectral features found in normalized radiance are quantified by introducing 15 parameters. These 15 parameters form the basis of a new generalized retrieval obtaining cloud optical thickness (τ), effective radius (r_e), and thermodynamic phase (&phis;). When applied to a liquid water cloud case, this retrieval matched a measured transmittance spectrum with a smaller root mean square difference over the entire spectrum (3.1%) than two other methods (up to 6.4%). To quantify the retrieval over all possible combinations of τ, r_e, and &phis;, simulated measurements were used in conjunction with realistic measurement and model error characteristics. By combining these error characteristics within the GEneralized Nonlinear Retrieval Analysis (GENRA) a solution probability distributions can be built. The information of cloud properties contained within cloud-transmitted radiance is greater on average for liquid water clouds than for ice clouds. For all possible combinations of cloud properties, radiance transmitted through clouds with τ<20 contain the most information on cloud properties, indicating that the 15 parameters have greatest sensitivity to cloud properties of optically thin clouds (τ<20). Of the 15 parameters, only 10 are required to retrieve accurately τ, r_e, and &phis; for any cloud except for ice clouds with τ>25 and r_e>30 μm. Using this retrieval, the correct thermodynamic phase is determined from transmittance with a probability greater than 99.4% for horizontally homogeneous clouds that contain either ice or liquid water cloud particles.

It is now well established that aerosols, by scattering and absorbing solar radiation, affect the terrestrial heat engine. Depending on the net relfectivity and absorptivity of the haze column and on the surface albedo, the net effect could be a cooling or a warming. But better understanding of the influence of aerosols is handicapped by lack of data and by the fact that their composition and distribution is highly variable in space and time. For the same reasons, the incorporation of aerosols in climate models is usually rudimentary.
We have in-situ measurements of the vertical profile and size distribution of aerosols ($>$0.09 $ mu$m in radius) taken over several places in eastern Canada at different times of the year. These data have been incorporated in a simple multi-layer radiative transfer model to estimate the effects of aerosols on the local radiation budget. A broad range of refractive indexes has been used and the increase of the particles size with the relative humidity is included.

Atmospheric particles are ubiquitous in the Earth’s atmosphere and have potential to influence atmospheric chemistry, visibility, global climate and human health, particularly downwind from major pollution sources. The main objective of this thesis was to investigate questions pertaining to the microphysical, chemical and optical properties of aerosol particles by using in situ data collected during four experiments carried out in different regions of the Northern Hemisphere.

The first two papers of this thesis reports on airborne measurements of the aerosol optical properties performed over the North Atlantic and the Los Angeles basin. Airmasses from Europe and North Africa are usually advected in over the North Atlantic, alternating with the background marine conditions. The results showed that the aerosols are not uniformly distributed in the area and variability in the aerosol fields occurs at sub-synoptic scales. It was also observed that the single scattering coefficient varied as the polluted plumes aged, suggesting a relationship between this quantity and transport time. The measurements performed around the Los Angeles basin showed that the area’s complex topography and local meteorological circulations exert a strong control on the distribution of the aerosol in the basin. Large spatio-temporal gradients in the aerosol optical properties were observed along a transect flown from the shore towards the mountains. Profiles flown over sites located on the mountains displayed a stratified configuration with elevated aerosol layers.

Airborne data of residual particles collected in orographic wave clouds over Scandinavia were analyzed using a single particle analysis technique. Mineral dust, organic aerosols and sea salt were the main group of particles identified. Residuals composed predominantly of mineral dust were found in glaciated clouds while organic residuals were found in liquid clouds. The results suggest that organic material may inhibit freezing and have considerable influence on supercooled clouds that form through heterogeneous pathways.

The partitioning of the aerosol particles between cloud droplets and interstitial air has been addressed in terms of their microphysical properties using data obtained at a mountain-top site in Sweden during a stratocumulus event. The results showed that the scavenging efficiency varied during the cloud event, and Aitken-mode particles were also efficiently scavenged in addition to accumulation-mode particles. It is hypothesized that alterations of the aerosol chemical composition occurred during the measurement period, modifying the hygroscopic nature of the particles and decreasing their activation diameter.

The knowledge of the optical and microphysical properties of aerosol particles in the atmosphere is relevant in various scientific fields from public health issues to climate modeling. A retrieval method is presented that estimates the single scattering albedo and asymmetry parameter of aerosol particles in regions of high pollution using spectral ground-based radiance and irradiance measurements, radiative transfer simulations, and a priori knowledge of the aerosol optical depth (AOD) derived from sun photometer observations. The used measurement data originated from the Pearl River Delta in China. The results are compared with sun photometer data and show a high agreement for AODs larger than 0.5. For low AODs and for cloudy conditions the method did not work due to the strong sensitivity of the initial parameters.
Kenntnisse über optische und mikrophysikalische Eigenschaften von Aerosolpartikeln in der Atmosphäre werden in vielen verschiedenen wissenschaftlichen Gebieten benötigt. Diese reichen vom Gesundheitswesen bis hin zur Klimamodellierung. Deswegen wird im Folgenden eine Ableitungsmethode vorgestellt, die die Einfachstreualbedo und Asymmtrieparameter von Aerosolpartikeln bestimmt. Diese Methode wurde dabei für Messungen im Pearl River Delta, China, in denen oft hohe Luftverschmutzungen auftreten, angewandt. Es werden dazu bodengebundene Messungen der spektralen abwärtsgerichteten Strahlungsflussdichte und Strahldichte, gekoppelt mit Strahlungsübertragungsrechnungen durchgeführt. Um die aerosoloptischen Parameter ableiten zu können, wird als zusätzliche Randbedingung die aerosol-optische Dicke (AOD) benötigt. Sonnenphotometermessungen liefern dabei zum einen die AOD und zum anderen die aerosoloptische Eigenschaften, die mit den Ergebnissen der Ableitungsmethode verglichen werden. Dabei wurden für große AOD-Werte (über 0.5) gute Übereinstimmungen zwischen beiden Methoden festgestellt werden. Für AOD-Werte kleiner als 0.5 und bei bewölkten Bedingungen zeigt die Methode große Unsicherheiten, weil die Parameter zu empfindlich auf diese Begebenheiten reagieren.

The Intergovernmental Panel on Climate Change (IPCC) has reported that in the southeastern US and eastern China, the general greenhouse warming due to anthropogenic gaseous emissions is dominated by the cooling effect of anthropogenic aerosols. To verify this model prediction in eastern China and southeastern US, we analyzed regional patterns of climate changes at 72 stations in eastern China during 1951-94 (44 years), and at 52 stations in the southeastern US during 1949-94 (46 years) to detect the fingerprint of aerosol radiative forcing. It was found that the mean rates of change of annual mean daily, maximum, minimum temperatures and diurnal temperature range (DTR) in eastern China were 0.8, -0.2, 1.8, and -2.0 C/100 years respectively, while the mean rates of change of annual mean daily, maximum, minimum temperatures and DTR in the southeastern US were -0.2, -0.6, 0.2, and -0.8 C/100 years, respectively. This indicates that the high rate of increase in annual mean minimum temperature in eastern China results in a slightly warming trend of daily temperature, while the high rate of decrease in annual mean maximum temperature and low rate of increase in annual mean minimum temperature lead to the cooling trend of daily temperature in the southeastern US. We found that the warming from the longwave forcing due to both greenhouse gases and aerosols was completely counteracted by the shortwave aerosol forcing in the southeastern US in the past 46 years. A slightly overall warming trend in eastern China is evident; winters have become milder. This finding is explained by hypothesizing that increasing energy usage during the past 44 years has resulted in more coal and biomass burning, thus increasing the emission of absorbing soot and organic aerosols in eastern China. Such emissions, in addition to well-known Asia dust and greenhouse gases, may be responsible for the winter warming trend in eastern China that we have reported here.The sensitivity of aerosol radiative properties to aerosol composition, size distribution, relative humidity (RH) is examined for the following aerosol systems: inorganic and organic ions (Cl-, Br-, NO3-, SO42-, Na+, NH4+, K+, Ca2+, Mg2+, HCOO-, CH3COO-, CH3CH2COO-, CH3COCOO-, OOCCOO2-, MSA-1); water-insoluble inorganic and organic compounds (elemental carbon, n-alkanes, SiO2, Al2O3, Fe2O3 and other organic compounds). The partial molar refraction method was used to calculate the real part of the refractive index. It was found that the asymmetry factor increased by ~48% with the real part varying from 1.40 to 1.65, and the single scattering albedo decreased by 24% with the imaginary part varying from -0.005 to -0.1. The asymmetry factor increased by 5.4 times with the geometric standard deviation varying from 1.2 to 3.0. The radiation transmission is very sensitive to the change in size distribution; other factors are not as significant.To determine the aerosol direct radiative forcing (ADRF), the aerosol optical depth (AOD) values at the three operational wavelengths (415, 500 and 673 nm) were determined at a regionally representative site, namely, Mt. Gibbs (35.780 N, 82.290 W, elevation 2006 m) in Mt. Mitchell State Park, NC, and a site located in an adjacent valley (Black Mountain, 35.660 N, 82.380 W, elevation 951 m) in the southeastern US. The two sites are separated horizontally by 10 km and vertically by 1 km. It was found that the representative total AOD values at 500 nm at the valley site for highly polluted (HP), marine (M) and continental (C) air masses were 0.68+/-0.33, 0.29+/-0.19 and 0.10+/-0.04, respectively. A search-graph method was used to retrieve the columnar size distribution (number concentration N, effective radius reff and geometric standard deviation sg) from the optical depth observations at three operational wavelengths. The ground albedo, single scattering albedo and imaginary part of the refractive index were calculated using a mathematically unique procedure involving a Mie code and a radiative transfer code in conjunction with the retrieved aerosol size distribution, AOD, and diffuse-direct irradiance ratio. It was found that N, reff and sg were in the ranges of 10 to 1.7x104 cm-3, 0.09 to 0.68 mm and 1.12 to 2.95, respectively. The asymmetry factor and single scattering albedo were in the ranges of 0.63 to 0.75 and 0.74 to 0.97 respectively. The ground albedo for the forested terrain and imaginary part of refractive index were found to be in the ranges of 0.06 to 0.29 and 0.005 to 0.051 respectively. On the basis of these aerosol radiative properties obtained at the research sites and computations using the Column Radiation Model (CRM) of National Center of Atmospheric Research (NCAR) Community Climate Model (CCM3), it was found that the average cloud-free 24-hour ADRF values were -13+/-8, -8+/3, -33+/-16 W m-2 for marine, continental, and polluted air masses, respectively. On the assumption that the fractional coverage of clouds is 0.61, it was estimated that the annual mean ADRF was 7+/-2 W m-2 in the southeastern US.The review with respect to the current knowledge of organic acids shows that aerosol formate and acetate concentrations range from 0.02 to 5.3 nmol/m3 and from 0.03 to 12.4 nmol/m3 respectively, and that between 34% to 77% of formate and between 21% to 66% of acetate are present in the fine fraction of aerosols. It was found that although most (98-99%) of these volatile organic acids were present in the gas phase, their concentrations in the aerosol particles were sufficient to make them a good candidate for cloud condensation nuclei (CCN). It is hypothesized that organic acids are at least one of the primary sources of CCN in the atmosphere due to their ubiquitous presence in the troposphere, especially over the continental forested areas. The results of our measurements at Palmer Station, Antarctica show that the daily average CCN concentrations at 0.3% and 1% supersaturations ranged from 0.3 to 160 cm-3 and from 4 to 168 cm-3, respectively, during the period from 17 January to 26 February, 1994. New evidence for substantial and definitive CCN enhancement near and within cloud has been observed at Mt. Mitchell, North Carolina. The results show that the average monthly CCN concentrations were 460+/-217, 386+/-286, 429+/-228 and 238+/-134 cm-3 for in-cloud, overcast, clear and rainy conditions, respectively. The typical CCN spectra show that there were a lot of small CCN produced and the ion concentrations (especially H+ and SO42-) were very high during the CCN enhancement period. The significantly positive correlation between black carbon (BC) and CCN at 1% supersaturation indicates that a percentage of the BC measured at the site may be in the form of an internal mixture and participated in the formation of CCN.

Uncertainties in aerosol radiative forcings, especially those associated with clouds, contribute to a large extent to uncertainties in the total anthropogenic forcing. The interaction of aerosols with clouds and radiation introduces feedbacks which can affect the rate of precipitation formation. In former assessments of aerosol radiative forcings, these effects have not been quantified. Also, with global aerosol-climate models simulating interactively aerosols and cloud microphysical properties, a quantification of the aerosol forcings in the traditional way is difficult to define properly. Here we argue that fast feedbacks should be included because they act quickly compared with the time scale of global warming. We show that for different forcing agents (aerosols and greenhouse gases) the radiative forcings as traditionally defined agree rather well with estimates from a method, here referred to as radiative flux perturbations (RFP), that takes these fast feedbacks and interactions into account. Based on our results, we recommend RFP as a valid option to compare different forcing agents, and to compare the effects of particular forcing agents in different models.

Solar radiation scattered within the atmosphere by atmospheric particles and aerosol particles has been investigated with regard to their state of polarization. Therefore measurements are performed with the COmpact RAdiation measurement System CORAS to analyze the individual components of the Stokes vector describing the measured radiation. For this purpose new optical inlets including a polarization filter have been developed. In parallel, radiative transfer simulations are conducted to interpret the measurements. For this purpose, two different radiative transfer solvers (SCIATRAN and polRadtran) were used. The simulations have been compared with the measurements to characterize the aerosol optical thickness and the predominant aerosol type.

Among anthropogenic perturbations of the Earth\'s atmosphere, greenhouse gases and aerosols are considered to have a major impact on the energy budget through their impact on radiative fluxes. We use three ensembles of simulations with the LMDZ general circulation model to investigate the radiative impacts of five species of greenhouse gases (CO2, CH4, N2O, CFC-11 and CFC-12) and sulfate aerosols for the period 1930-1989. Since our focus is on the atmospheric changes in clouds and radiation from greenhouse gases and aerosols, we prescribed sea surface temperatures in these simulations. Besides the direct impact on radiation through the greenhouse effect and scattering of sunlight by aerosols, strong radiative impacts of both perturbations through changes in cloudiness are analysed. The increase in greenhouse gas concentration leads to a reduction of clouds at all atmospheric levels, thus decreasing the total greenhouse effect in the longwave spectrum and increasing absorption of solar radiation by reduction of cloud albedo. Increasing anthropogenic aerosol burden results in a decrease in high-level cloud cover through a cooling of the atmosphere, and an increase in the low-level cloud cover through the second aerosol indirect effect. The trend in low-level cloud lifetime due to aerosols is quantified to 0.5 min day-1 decade-1 for the simulation period. The different changes in high (decrease) and low-level (increase) cloudiness due to the response of cloud processes to aerosols impact shortwave radiation in a contrariwise manner, and the net effect is slightly positive. The total aerosol effect including also the aerosol direct and first indirect effects remains strongly negative.

In this study we examine the performance of 31 global model radiative transfer schemes in cloudfree conditions with prescribed gaseous absorbers and no aerosols (Rayleigh atmosphere), with prescribed scatteringonly aerosols, and with more absorbing aerosols. Results are compared to benchmark results from high-resolution, multiangular line-by-line radiation models. For purely scattering aerosols, model bias relative to the line-by-line models in the top-of-the atmosphere aerosol radiative forcing ranges from roughly −10 to 20 %, with over- and underestimates of radiative cooling at lower and higher solar zenith angle, respectively. Inter-model diversity (relative standard deviation) increases from ~ 10 to 15% as solar zenith angle decreases. Inter-model diversity in atmospheric and surface forcing decreases with increased aerosol absorption, indicating that the treatment of multiple-scattering is more variable than aerosol absorption in the models considered. Aerosol radiative forcing results from multi-stream models are generally in better agreement with the line-by-line results than the simpler two-stream schemes. Considering radiative fluxes, model performance is generally the same or slightly better than results from previous radiation scheme intercomparisons. However, the inter-model diversity in aerosol radiative forcing remains large, primarily as a result of the treatment of multiple-scattering. Results indicate that global models that estimate aerosol radiative forcing with two-stream radiation schemes may be subject to persistent biases introduced by these schemes, particularly for regional aerosol forcing.

Este trabalho tem como foco o entendimento das propriedades ópticas do aerossol na Amazônia utilizando várias técnicas: sensoriamento remoto em solo, sensoriamento remoto por satélites e medidas in situ. Propriedades ópticas medidas continuamente ao longo de mais de 15 anos pela rede AERONET na Amazônia foram analisadas buscando compreender como os eventos anuais de queima de biomassa e as emissões urbanas de Manaus afetam as propriedades das partículas. Medidas de longo prazo do sensor MODIS utilizando o sistema Giovanni da NASA foram úteis para caracterizar o impacto da pluma urbana de Manaus nas propriedades de aerossol e nuvens na Amazônia Central. A partir de medições in situ realizadas nas várias estações amostradoras do experimento GoAmazon2014/5, analisou-se em detalhes propriedades de absorção e espalhamento de aerossol antes e depois do impacto da pluma urbana de Manaus. Foi observada uma alta variabilidade na profundidade óptica do aerossol (AOD) bem como em outras propriedades, tais como absorção, espalhamento e distribuição de tamanho. Valores muito elevados de AOD foram observados em todos os sítios durante a estação seca, em particular na região do arco do desflorestamento. Análises dos expoentes Ångström de espalhamento e absorção separam as diferentes componentes absorvedoras do aerossol, entre eles o carbono elementar (EC), carbono orgânico (OC), poeira mineral e partículas biogênicas. Uma análise da forçante radiativa no topo da atmosfera em conjunto com a Matriz Ångström auxiliou no entendimento do papel da componente orgânica de espalhamento (OC) e da componente de absorção (BC) no aerossol de queimadas e urbano na forçante radiativa. A região menos afetada por queimadas na Amazônia foi caracterizada pela presença de um aerossol altamente espalhador durante a estação seca, com valores de albedo de espalhamento simples (SSA) na faixa de 0,91-0,94. Por outro lado, constatou-se valores médios de 0,85 a 0,89 em regiões fortemente impactadas por queimadas. Através de medidas in situ e medidas obtidas a partir da rede AERONET, foi possível observar significativo impacto da pluma de Manaus vento abaixo da cidade, especialmente na componente de absorção. O efeito da absorção do aerossol urbano na forçante radiativa é significativo, indo de uma forçante no sítio da EMBRAPA, antes da pluma, de -24 W/m² para cerca de -18 W/m² em Manacapuru, com o efeito da pluma de Manaus. A partir da análise de 12 anos de medidas dos sensores MODIS e MISR, observou-se alterações nas propriedades de nuvens e na carga atmosférica de aerossol. Foram analisadas a AOD, a temperatura do topo da nuvem e o raio efeito de gotículas de nuvens. Ficou clara a presença de nuvens mais altas e com raio efetivo menor em regiões com maior carga de aerossol, vento abaixo de Manaus.
This work focuses on understanding the optical properties of aerosol in the Amazon, using various techniques: remote sensing from the ground, remote sensing from satellites and in situ measurements. Aerosol optical properties continuously measured over more than 15 years carried out by the AERONET network in the Amazon were analyzed seeking to understand how the annual biomass burning emissions and urban emissions of Manaus affect particle properties. Long-term measurements of MODIS using the Giovanni NASA system were useful to characterize the impact of the urban plume of Manaus in the properties of aerosol and clouds in the central Amazon. Based on in situ measurements in the various sampling sites of the GoAmazon2014/5 experiment, the absorption and scattering properties of aerosol before and after the impact of Manaus urban plume were analyzed in detail. It was observed a large spatial and temporal variability in the aerosol optical depth (AOD) as well as in various properties such as absorption and scattering coefficients and size distribution. Very high levels of AOD were observed at all sites during the dry season, particularly in the deforestation arc region. Analysis of scattering and absorption Ångström exponents helps to identify different absorber components of the aerosol, including elemental carbon (EC), organic carbon (OC), mineral dust and biogenic particles. An analysis of the radiative forcing at the top of the atmosphere together with the Ångström Matrix helps in understanding the role of the scattering organic component (OC) versus the absorption component (BC) in biomass burning and urban aerosol particles in the radiative forcing. The region least affected by fires in the Amazon was characterized by a highly scattering aerosol during the dry season with Single Scattering Albedo (SSA) values in the range of 0.91-0.94, while we found mean values of 0.85 to 0.89 in heavily affected biomass burning regions. Through in situ measurements and AERONET observations it was possible to measure the significant impact of Manaus plume downwind of the urban area, especially in the absorption component. The effect of absorption of urban aerosol in the radiative forcing is significant, with measurements at the EMBRAPA site, before the impact of the plume, at -24 W/m² going to -18 W/m² in Manacapuru that is effect of the Manaus plume. It was also analyzed the changes in the properties of clouds and atmospheric aerosol loading over the last 12 years of MODIS and MISR measurements. The analysis of AOD, cloud top temperature and the radius of cloud droplets show a clear signal of Manaus plume. It was observed clouds with smaller effective radius in regions with higher aerosol load, downwind of Manaus.

Among anthropogenic perturbations of the Earth\''s atmosphere, greenhouse gases and aerosols are considered to have a major impact on the energy budget through their impact on radiative fluxes. We use three ensembles of simulations with the LMDZ general circulation model to investigate the radiative impacts of five species of greenhouse gases (CO2, CH4, N2O, CFC-11 and CFC-12) and sulfate aerosols for the period 1930-1989. Since our focus is on the atmospheric changes in clouds and radiation from greenhouse gases and aerosols, we prescribed sea surface temperatures in these simulations. Besides the direct impact on radiation through the greenhouse effect and scattering of sunlight by aerosols, strong radiative impacts of both perturbations through changes in cloudiness are analysed. The increase in greenhouse gas concentration leads to a reduction of clouds at all atmospheric levels, thus decreasing the total greenhouse effect in the longwave spectrum and increasing absorption of solar radiation by reduction of cloud albedo. Increasing anthropogenic aerosol burden results in a decrease in high-level cloud cover through a cooling of the atmosphere, and an increase in the low-level cloud cover through the second aerosol indirect effect. The trend in low-level cloud lifetime due to aerosols is quantified to 0.5 min day-1 decade-1 for the simulation period. The different changes in high (decrease) and low-level (increase) cloudiness due to the response of cloud processes to aerosols impact shortwave radiation in a contrariwise manner, and the net effect is slightly positive. The total aerosol effect including also the aerosol direct and first indirect effects remains strongly negative.

The indirect effects of anthropogenic aerosols—through their interactions with clouds—are currently one of the most uncertain perturbations to the radiative energy balance at the top of the atmosphere. A crucial link between aerosol and cloud is that aerosols can act as cloud condensation nuclei (CCN). This microphysical process must be parameterised if the large-scale effects are to be represented in a general circulation model (GCM). Theoretical work presented in this thesis highlights the importance of incorporating the kinetic limitations on droplet formation in aerosol activation parameterisations. HadGEM-UKCA is a GCM, capable of representing the chemical and microphysical aerosol processes required to model CCN accurately. The author has incorporated a Köhler theory based parameterisation of aerosol activation into HadGEM-UKCA, to facilitate quantitative predictions of the indirect aerosol effects. This thesis presents an estimate of the range of uncertainty in such predictions attributable to the choice of parameterisation of the sub-grid-scale variability of vertical velocity. Results of simulations demonstrate that the use of a characteristic updraught velocity cannot replicate results derived with a distribution of vertical velocities, and is to be discouraged in GCMs. Consequently, work focuses on the effect of the variance (σ_w²) of a Gaussian pdf of vertical velocity. Fixed values of σ_w and a configuration in which σ_w depends on turbulent kinetic energy are tested. Results from the mid-range fixed σ_w and TKE-based configurations both compare well with vertical velocity distributions and cloud droplet number concentrations measured in situ. However, the sparse set of available measurements does not provide enough of a constraint to recommend one or the other as the best configuration globally. The radiative flux perturbation (RFP) due to the total effects of anthropogenic aerosol is estimated at −1.7Wm⁻² for the TKE-based configuration. To the extent that it is valid to decouple the individual aerosol effects, the direct effect accounts for approximately −0.6Wm⁻² of the total, the cloud albedo effect −0.8Wm⁻² and the cloud lifetime effect −0.3Wm⁻², indicating that these effects are additive within HadGEM-UKCA. Total aerosol RFP ranges from −1.4Wm⁻² from simulations with σ_w=0.1ms⁻¹, up to −2.0Wm⁻² for σ_w=0.7ms⁻¹. This range of 0.6Wm⁻² corresponds to almost a third of the total estimate of −1.9Wm⁻², obtained with the mid-range value of σ_w=0.4ms⁻¹. Reducing the uncertainty in the parameterisation of σ_w is therefore an important step towards reducing the uncertainty in estimates of the indirect aerosol effects.

Thesis (Ph.D)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2009.
Committee Chair: Fu, Rong; Committee Member: Dickinson, Robert E.; Committee Member: Nenes, Athanasios; Committee Member: Webster,Peter J.; Committee Member: Yu, Hongbin. Part of the SMARTech Electronic Thesis and Dissertation Collection.

xv, 165 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.
The amount of solar radiation at the earth's surface is modulated by fluctuations in aerosol density and cloud optical depth--two uncertain factors in climate change studies. The University of Oregon Solar Radiation Monitoring Lab has collected five-minute resolution surface shortwave irradiance measurements at three sites in Oregon since 1980 or earlier. Direct normal surface solar irradiance has increased 4-5% per decade (8-11 W/m 2 per decade) at these three sites since 1980 (1979 in Eugene). Total solar irradiance has likewise increased by 1-2% per decade (2-3 W/m 2 per decade). This unusually long direct normal time series was used to examine the causes of trends because of its high sensitivity to scattering and high instrumental accuracy. The strongest factor causing direct normal irradiance trends was found to be the high stratospheric aerosol concentrations after the volcanic eruptions of El Chichà à à à ³n (1982) and Mt. Pinatubo (1991). Removing the four years most impacted by each volcanic eruption (1982-1985 and 1991-1994) reduces the trend in annual average direct normal irradiance by 20-55%, depending on the site. All measurement sites show low irradiance values before the volcanic eruption of El Chichà à à à ³n in 1982 compared to later periods of relatively low volcanic aerosols (1989- 1990, and 2000-2007). These low values are visible both in all-sky and clear-sky monthly averages, suggesting high aerosol loads as a likely cause. Clear-sky direct normal irradiance measurements from high solar zenith angles (6575à à à à °) are analyzed to test the hypothesis that the increase in irradiance comes from a reduction of anthropogenic aerosols since the late 1980s. No change in anthropogenic aerosols between 1987 and 2007 is detectable within the noise of the data. Even after removing the four years most heavily impacted by volcanic eruptions, the continued reduction of volcanic aerosol loads causes over half of the clear-sky direct normal irradiance increase since 1987. The remaining increase could be accounted for by a 20-year decrease in 550 nm aerosol optical depth of .005 à à à à ± .005, or 6% à à à à ± 6%, but considerable statistical uncertainty exists.
Adviser: Gregory Bothun

Aerosols contribute the largest uncertainty to estimates of radiative forcing of the Earth’s atmosphere, which are thought to exert a net negative radiative forcing, offsetting a potentially significant but poorly constrained fraction of the positive radiative forcing associated with greenhouse gases. Aerosols perturb the Earth’s radiative balance directly by absorbing and scattering radiation and indirectly by acting as cloud condensation nuclei, altering cloud albedo and potentially cloud lifetime. One of the major factors governing the uncertainty in estimates of aerosol direct radiative forcing is the poorly constrained aerosol single scattering albedo, which is the ratio of the aerosol scattering to extinction. In this thesis, I describe a new instrument for the measurement of aerosol optical properties using photoacoustic and cavity ring-down spectroscopy. Characterisation is performed by assessing the instrument minimum sensitivity and accuracy as well as verifying the accuracy of its calibration procedure. The instrument and calibration accuracies are assessed by comparing modelled to measured optical properties of well-characterised laboratory-generated aerosol. I then examine biases in traditional, filter-based absorption measurements by comparing to photoacoustic spectrometer absorption measurements for a range of aerosol sources at multiple wavelengths. Filter-based measurements consistently overestimate absorption although the bias magnitude is strongly source-dependent. Biases are consistently lowest when an advanced correction scheme is applied, irrespective of wavelength or aerosol source. Lastly, I assess the sensitivity of the direct radiative effect of biomass burning aerosols to aerosol and cloud optical properties over the Southeast Atlantic Ocean using a combination of offline radiative transfer modelling, satellite observations and global climate model simulations. Although the direct radiative effect depends on aerosol and cloud optical properties in a non-linear way, it appears to be only weakly dependent on sub-grid variability.

Nucleation from the gas phase is an important source of aerosol particles in the Earth’s atmosphere, contributing to the number of cloud condensation nuclei, which form cloud droplets. We have implemented in the aerosolclimate model ECHAM5-HAM a new scheme for neutral and charged nucleation of sulfuric acid and water based on laboratory data, and nucleation of an organic compound and sulfuric acid using a parametrization of cluster activation based on field measurements. We give details of the implementation, compare results with observations, and investigate the role of the individual aerosol nucleation mechanisms for clouds and the Earth’s radiative forcing. The results of our simulations are most consistent with observations when neutral and charged nucleation of sulfuric acid proceed throughout the troposphere and nucleation due to cluster activation is limited to the forested boundary layer. The globally averaged annual mean contributions of the individual nucleation processes to total absorbed solar short-wave radiation via the direct, semi-direct, indirect cloud-albedo and cloud-lifetime effects in our simulations are −1.15 W/m2 for charged H2SO4/H2O nucleation, −0.235 W/m2 for cluster activation, and −0.05 W/m2 for neutral H2SO4/H2O nucleation. The overall effect of nucleation is −2.55 W/m2, which exceeds the sum of the individual terms due to feedbacks and interactions in the model. Aerosol nucleation contributes over the oceans with −2.18 W/m2 to total absorbed solar short-wave radiation, compared to −0.37 W/m2 over land. We explain the higher effect of aerosol nucleation on Earth’s radiative forcing over the oceans with the larger area covered by ocean clouds, due to the larger contrast in albedo between clouds and the ocean surface compared to continents, and the larger susceptibility of pristine clouds owing to the saturation of effects. The large effect of charged nucleation in our simulations is not in contradiction with small effects seen in local measurements: over southern Finland, where cluster activation proceeds efficiently, we find that charged nucleation of sulfuric acid and water contributes on average less than 10% to ultrafine aerosol concentrations, in good agreement with observations.

This thesis explores the factors controlling the distribution of black carbon (BC) in the atmosphere/troposphere and its implications for climate forcing. BC is of great climate interest because of its warming potential. Estimates of BC climate forcing have large uncertainty, in part due to poor knowledge of the distribution of BC in the atmosphere. This dissertation first examines the factors controlling the sources of BC in the Arctic in winter and spring using a global chemical transport model (GEOS-Chem). Emission inventories of BC and wet scavenging of aerosols in the model are updated to reproduce observed atmospheric concentrations of BC as well as observed snow BC content in the Arctic in winter-spring. The simulation shows a dominant contribution of fuel (fossil fuel and biofuel) combustion to BC in Arctic spring. Arctic snow BC content is dominated by fuel combustion sources in winter, but has equal contributions from open fires and fuel combustion in spring. The estimated decrease in Arctic snow albedo due to BC deposition in spring is 0.6%, resulting in a regional surface radiative forcing of 1.2 W m-2. The dissertation then extends the evaluation of the BC simulation to the global scale using aircraft observations over source regions, continental outflow and remote regions and ground-based measurements. The observed low BC concentrations over the remote oceans imply more efficient BC removal than is currently implemented in models. The simulation that has total BC emissions of 6.5 Tg C a-1 and a mean tropospheric lifetime of 4.2 days for 2009 (vs. 6.8 ± 1.8 days for the AeroCom models) captures the principal features of observed BC. The simulation estimates a global mean BC absorbing aerosol optical depth of 0.0017 and a top-of-atmosphere direct radiative forcing (DRF) of 0.19 W m-2, with a range of 0.17-0.31 W m-2 based on uncertainties in the BC atmospheric distribution. The DRF is lower than previous estimates, which could be biased high because of excessive BC concentrations over the oceans and in the free troposphere.
Engineering and Applied Sciences

Nucleation from the gas phase is an important source of aerosol particles in the Earth’s atmosphere, contributing to the number of cloud condensation nuclei, which form cloud droplets. We have implemented in the aerosolclimate model ECHAM5-HAM a new scheme for neutral and charged nucleation of sulfuric acid and water based on laboratory data, and nucleation of an organic compound and sulfuric acid using a parametrization of cluster activation based on field measurements. We give details of the implementation, compare results with observations, and investigate the role of the individual aerosol nucleation mechanisms for clouds and the Earth’s radiative forcing. The results of our simulations are most consistent with observations when neutral and charged nucleation of sulfuric acid proceed throughout the troposphere and nucleation due to cluster activation is limited to the forested boundary layer. The globally averaged annual mean contributions of the individual nucleation processes to total absorbed solar short-wave radiation via the direct, semi-direct, indirect cloud-albedo and cloud-lifetime effects in our simulations are −1.15 W/m2 for charged H2SO4/H2O nucleation, −0.235 W/m2 for cluster activation, and −0.05 W/m2 for neutral H2SO4/H2O nucleation. The overall effect of nucleation is −2.55 W/m2, which exceeds the sum of the individual terms due to feedbacks and interactions in the model. Aerosol nucleation contributes over the oceans with −2.18 W/m2 to total absorbed solar short-wave radiation, compared to −0.37 W/m2 over land. We explain the higher effect of aerosol nucleation on Earth’s radiative forcing over the oceans with the larger area covered by ocean clouds, due to the larger contrast in albedo between clouds and the ocean surface compared to continents, and the larger susceptibility of pristine clouds owing to the saturation of effects. The large effect of charged nucleation in our simulations is not in contradiction with small effects seen in local measurements: over southern Finland, where cluster activation proceeds efficiently, we find that charged nucleation of sulfuric acid and water contributes on average less than 10% to ultrafine aerosol concentrations, in good agreement with observations.

In this study we examine the performance of 31 global model radiative transfer schemes in cloudfree conditions with prescribed gaseous absorbers and no aerosols (Rayleigh atmosphere), with prescribed scatteringonly aerosols, and with more absorbing aerosols. Results are compared to benchmark results from high-resolution, multiangular line-by-line radiation models. For purely scattering aerosols, model bias relative to the line-by-line models in the top-of-the atmosphere aerosol radiative forcing ranges from roughly −10 to 20 %, with over- and underestimates of radiative cooling at lower and higher solar zenith angle, respectively. Inter-model diversity (relative standard deviation) increases from ~ 10 to 15% as solar zenith angle decreases. Inter-model diversity in atmospheric and surface forcing decreases with increased aerosol absorption, indicating that the treatment of multiple-scattering is more variable than aerosol absorption in the models considered. Aerosol radiative forcing results from multi-stream models are generally in better agreement with the line-by-line results than the simpler two-stream schemes. Considering radiative fluxes, model performance is generally the same or slightly better than results from previous radiation scheme intercomparisons. However, the inter-model diversity in aerosol radiative forcing remains large, primarily as a result of the treatment of multiple-scattering. Results indicate that global models that estimate aerosol radiative forcing with two-stream radiation schemes may be subject to persistent biases introduced by these schemes, particularly for regional aerosol forcing.

Soot particles are a major absorber of shortwave radiation in the atmosphere. They exert a rather uncertain direct and semi-direct radiative effect, which causes a heating or in some cases a cooling of the atmosphere. The mass absorption coefficient is an essential quantity to describe this light absorption process. This work presents new experimental data on the mass absorption coefficient of soot particles in the troposphere over Central Europe. Mass absorption coefficients were derived as the ratio between the light absorption coefficient determined by multi angle absorption photometry (MAAP), and the soot mass concentration determined by Raman spectroscopy. The Raman method is sensitive to graphitic structures present in the particle samples, and was calibrated in the laboratory using Printex90 model particles. The mass absorption coefficients were determined for a number of seven observation sites, ranging between 3.9 and 7.4 m²/g depending on measurement site and observational period. The highest values were found in an continentally aged air mass in winter, where we presumed soot particles to be present mainly in internal mixture. The regional model WRF-Chem was used in conjunction with a high resolution soot emission inventory to simulate soot mass concentrations and absorption coefficients for the Central European Troposphere. The model was validated using soot mass concentrations from Raman measurements and absorption coefficients. Simulated soot mass concentrations were found to be too low by around 50 %, which could be improved by scaling the emissions by a factor of two. In contrast, the absorption coefficient was positively biased by around 20%. Adjusting the modeled mass absorption coefficient to measurements, the simulation of soot light absorption was improved. Finally, the positive direct radiative forcing at top of the atmosphere was found to be lowered by up to 70% for the model run with adjusted soot absorption behaviour, , indicating a decreased heating effect on the atmosphere.

Chargée de brume photochimique, l'atmosphère de Titan est le siège d'une activité dynamique complexe évoluant lentement au gré des saisons. Tout comme la couche d'ozone sur Terre, la couche détachée sur Titan est une fine bande d'aérosols englobant la partie la plus externe de son atmosphère. Depuis sa découverte par les sondes Voyager dans les années 80, elle attise les curiosités quant à sa composition et ses mécanismes de formation.Grâce à la sonde Cassini, en orbite autour de Saturne depuis 2004, nous avons une opportunité unique de l'observer sur près d'une demie année titanienne. Cette thèse vise à réaliser un suivi détaillé de la couche détachée sur l'ensemble de cette mission en s'appuyant sur les relevés réalisés par l'instrument ISS.Dans un premier temps, nous présentons la procédure de traitement mise en place pour calibrer et géo-référencer les données du PDS.Puis, nous réalisons une caractérisation des propriétés optiques des aérosols présents dans la couche détachée en couplant un modèle de diffusion par des agrégats fractals avec un modèle de transfert radiatif simplifié.Par la suite, ces nouvelles contraintes sont réutilisées pour réaliser une inversion globale des profils d'extinction de la brume en s'appuyant sur un modèle plus complexe de transfert radiatif au limbe. Ces relevés systématiques nous permettent de suivre l'évolution spatiale et temporelle de la couche détachée tout au long de la mission Cassini.Enfin, nous nous penchons tout particulièrement sur la disparition de la couche détachée au passage de l'équinoxe de printemps, suivi de sa réapparition en 2016, peu de temps avant le solstice d'été
Loaded with photochemical haze, Titan's dynamical atmosphere is slowly evolving through the seasons. Like the ozone layer on Earth, Titan's detached haze layer is a thin coat of aerosols surrounding the upper part of its atmosphere. Since its discovery in the 80's by Voyagers' flybys, it has raised many questions on its content and origin. Thanks to the Cassini mission orbiting around Saturn since 2004, we have the chance to track it over half a Titan year. This thesis carries out a complet survey on Titan's detached haze layer observations taken continuously by the ISS instrument during the whole mission.At first, we present the processing pipeline developed to calibrate and navigate the raw data coming the PDS.Then, we characterize the aerosols optical properties seen inside the detached haze layer by coupling a fractal aggregate model with a simplified version of the radiative transfer equation.Thereafter, these new constrains are used as input into a more complex radiative transfer model in the limb geometry in order to extract globally the extinction profiles of the haze in the upper atmosphere. These systematic surveys allow us to follow the spatial and temporal evolution of the detached haze layer from the beginning to the end of the Cassini mission.Finally, we took a special care on the disappearance of the detached haze after the vernal equinox and its recent reappearance in 2016, just before the summer solstice

Les mesures de l'éclairement solaire direct reçu au sol en incidence normale (DNI) par des pyrhéliomètres ou instruments équivalents incluent l'éclairement provenant de l'angle solide du disque solaire (DNIS) et celui provenant d'une région angulaire circumsolaire plus large, appelé éclairement circumsolaire (CSNI). Les instruments ont des demi-angles d'ouverture équivalents variant entre 2,5° et 5°, soit un ordre de grandeur plus grand que le demi-angle du disque solaire. Quant aux demi-angles des systèmes de production d'énergie concentrant les rayons solaires, ils sont plus grands que le demi-angle du disque solaire, et plus petits que ceux des instruments. Par consequent, le CSNI doit être connu pour une estimation précise du DNI. Cette thèse contribue à la connaissance et à la modélisation des éclairements direct et circumsolaire en milieu désertique par conditions de ciel clair. Après avoir déterminé les propiétés optiques des aérosols les plus influentes, le modèle numérique de transfert radiatif libRadtran a été utilisé pour modéliser le CSNI et le DNIS. Un modèle paramétrique simplifié et très rapide a été développé qui reproduit les résultats de libRadtran. Il estime le ratio circumsolaire (CSR), soit le rapport entre le CSNI et la somme du CSNI et du DNIS, à partir de mesures standards du DNI et de l'éclairement diffus. A partir du DNI mesuré et de CSR modélisé, le CSNI et le DNIS peuvent être estimés pour tout demi-angle entre 0,4° et 5°. Le modèle a été validé pour deux stations de mesure, dans les Emirats Arabes Unis et en Algérie
Routine measurements of the broadband direct normal irradiance (DNI), i.e. beam irradiance at normal incidence, by means of pyrheliometers or equivalent pyranometric systems include the irradiance originating from within the extent of the solar disc (DNIS) and that from a larger circumsolar region, called the circumsolar normal irradiance (CSNI). Such instruments have equivalent aperture half-angles between 2.5° and 5° which are one order of magnitude greater than the angular radius of the solar disc. The equivalent aperture half-angles of the concentrated solar powered systems are greater than the angular radius of the solar disc, but smaller than that of the measuring systems. Therefore, information on the CSNI should be provided for an improved assessment of the DNI. The objective of this PhD thesis is to contribute to an improved assessment of the beam and circumsolar radiation under cloud-free conditions in a desert environment. After selecting the aerosol optical properties of significance, the radiative transfer model libRadtran was used to model the CSNI and DNIS. A fast and simple parametric model which mimics the libRadtran values is proposed. This model uses standard measurements of the DNI and the diffuse horizontal irradiance as inputs to estimate the circumsolar ratio (CSR) for any aperture half-angle between 0.4° and 5°. The CSR is the ratio of the CSNI to the sum of the CSNI and the DNIS. Knowing the CSR and having the measured DNI, the CSNI and the DNIS can be computed

A avaliação dos efeitos dos aerossóis em relação ao balanço radiativo local e global bem como o impacto sobre a saúde humana, principalmente em grandes centros urbanos, demanda que se conheça de forma precisa a sua concentração e distribuição espaço-temporal. Neste contexto, o monitoramento acurado de longo prazo por estações instaladas ao redor do mundo tornou-se um desafio e uma necessidade para várias áreas do conhecimento. Classicamente as estações utilizam a técnica de fotometria solar para inferir a concentração e a distribuição de tamanho dos aerossóis através da profundidade óptica do aerossol (POA) e do coeficiente de Ångström . No presente trabalho é sugerida uma metodologia para estimar POA e do coeficiente de Ångström através de quatro canais espectrais de radiômetros do tipo Multi-Filter Rotating Shadowband Radiometer (MFRSR) que operam em São Paulo desde 1999. Estas estimativas foram avaliadas em relação à rede AErosol RObotic NETwork (AERONET) entre os anos de 2004 a 2006. Os resultados mostram que, em termos de variabilidade temporal da POA, há boa concordância entre os diferentes instrumentos. Entretanto, são encontradas diferenças médias sistemáticas da ordem de 0,03 na magnitude da POA em três dos quatro canais analisados, enquanto que o valor sugerido pela OMM para uma atmosfera limpa é de no máximo 0,02. Este resultado aponta que a metodologia empregada nos MFRSR fornece valores de boa qualidade. Ainda neste trabalho, foram relacionadas variáveis meteorológicas coletadas pela Estação Meteorológica do IAG-USP com a POA e o do coeficiente de Ångström estimados neste trabalho. Observou-se uma relação linear entre o coeficiente de Ångström e a umidade relativa (UR), indicando um crescimento do tamanho médio dos aerossóis que integram um grupo com 0,20The evaluation of the aerosol effects to the local and global radiation budget, as well as the impact on human health, particularly in large urban centers, demands knowing accurately their concentration and spatial-temporal distribution. In this context, the accurate long term monitoring from ground based stations installed around the world has become a challenge and a necessity for various areas of knowledge. Classically, the stations use the technique of Sun photometry to infer the concentration and size distribution of aerosols through the aerosol optical depth (AOD) and Ångström coefficient . In this paper we suggest a methodology to estimate AOD and Ångström coefficient through four channels of Multi-Filter Rotating Shadowband Radiometers (MFRSR) operating in Sao Paulo since 1999. These estimates were compared to the results of the AErosol RObotic NETwork (AERONET) between the years of 2004 to 2006. The results showed that the MFRSR can represent well the temporal variability of the AOD, but systematic differences were found with mean values of about 0.03 in AOD, in three of the four analyzed channels. The value suggested by WMO for clean air is at most 0.02. This result indicates that the methodology employed in MFRSR provides values of quality good. Also in this study, meteorological influences on the aerosol optical properties were analyzed. The meteorological variables were monitored at the Meteorological Station of the IAG-USP There was a linear relationship between Ångström coefficient and relative humidity (RH), indicating a growth of the average size of aerosols within a group with 0.20