Atmospheric haze, which builds up over South Africa including our study areas, Cape Town and the Mpumalanga Highveld under calm weather conditions, causes public concern. The scope of this study was to determine the concentration and composition of atmospheric aerosol at Khayelitsha (an urban site in the Western Cape) and Ferrobank (an industrial site in Witbank, Mpumalanga). Particulate matter was collected in Khayelitsha from 18 May 2007 to 20 July 2007 (i.e. 20 samples) using a Partisol-plus sampler and a Tapered Element Oscillating Microbalance (TEOM) sampler. Sampling took place at Ferrobank from 07 February 2008 to 11 March 2008 (6 samples) using a Partisol-plus sampler and an E-sampler. The gravimetric mass of each exposed sample was determined from pre- and post-sampling weighing. The elemental composition of the particulate matter was determined for 16 elements at Khayelitsha using Proton Induced X-ray Emission (PIXE). The concentration of the elements Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, As, Br, Sn, and Pb was determined by analysing the PIXE spectra obtained. In similar manner, the elemental composition of the particulate matter was determined for 15 elements at Ferrobank (Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, As, Br and Pb). The average aerosol mass concentrations for different days at the Khayelitsha site were found to vary between 8.5 μg/m3 and 124.38 μg/m3. At the Khayelitsha site on three occasions during the sampling campaign the average aerosol mass concentrations exceeded the current South African air quality standard of 75 μg/m3 over 24 h. At the Ferrobank site, there are no single days that exceeded the limit of the South African air quality standard during the sampling campaign. Enrichment factors for each element of the particles sampled with an aerodynamic diameter of less than 10 μm (PM10) samples have been calculated in order to identify their possible sources. The analysis yielded five potential sources of PM10 : soil dust, sea salt, gasoline emissions, domestic wood and coal combustion. Interestingly, enrichment factor values for the Khayelitsha samples show that sea salt constitutes a major source of emissions, while Ferrobank samples, the source apportionment by unique ratios (SPUR) indicate soil dust and coal emission are the major sources of pollution. The source apportionment at Khayelitsha shows that sea salt and biomass burning are major source of air pollution.

Muitos estudos têm sido desenvolvidos com o intuito de descrever a química da fase gasosa na atmosfera da Região Metropolitana de São Paulo (RMSP). Contudo, o tratamento do material particulado (PM) ainda é feito de forma simplificada em modelos de transporte e químicos atmosféricos, apesar do grande conhecimento já adquirido na caracterização da sua composição elementar e da sua estrutura física. Tendo isso em vista, o objetivo do presente estudo é identificar as principais fontes emissoras do material particulado fino, em especial as fontes veiculares que apresentam muitas dificuldades para sua identificação por não haver medidas de traçadores específicos para os combustíveis utilizados. Neste trabalho foram realizadas amostragens, que duravam 24 horas, próximas a uma avenida de intenso tráfego (Avenida Dr. Arnaldo, na Faculdade de Medicina da Universidade de São Paulo) no período de junho de 2007 a agosto de 2008. Com os dados de composição dessas amostras, a identificação das possíveis fontes foi realizada por modelos receptores; mais especificamente foram utilizados: Análise de Fatores (AF) e Positive Matrix Factorization (PMF), uma nova ferramenta estatística, que ainda não havia sido aplicada no estudo do material particulado em São Paulo. O número de fontes identificadas por essas duas ferramentas estatísticas não foi o mesmo: na AF foram extraídos 4 fatores (solo, queima de óleo combustível e dois fatores que se dividiram, identificando a emissão de veículos leves e pesados não diferenciados), enquanto que o PMF identificou 6 (as mesmas fontes identificadas pela AF, com a diferenciação da emissão veicular (leves e pesados) e ainda a queima de biomassa). Houve concordância entre as duas análises que a maior participação para formação de material particulado fino é da emissão por veículos. A comparação entre os modelos mostrou que os resultados obtidos pelo PMF apresentaram uma melhor divisão das fontes, principalmente na identificação das frotas veiculares. Isso se deve ao fato do PMF considerar na análise o erro de cada concentração medida como um peso para cada variável, além de não permitir a ocorrência de fatores negativos, caracterizando melhor as fontes através da presença desses vínculos físicos. / Several studies have been developed in order to describe the gaseous phase of atmospheric constituents in the Metropolitan Region of Sao Paulo (RMSP). However, the aerosol description remains simplified in chemical models, despite the knowledge acquired in its characterization and composition analyses. Facing these limitations, the objective of this work is to identify the main emission sources of fine particulate matter, specially the vehicular ones that present a lot of difficulties due to the fact that the characteristic trace elements are unknown for these sources. It was used in this work 201 samples collected in 24-hour period each at Dr. Arnaldo Avenue, a large and busy avenue in the city of São Paulo, from June 2007 to August 2008. The source identification was accomplished considering the samples composition and using receptor models: Factor Analysis (FA) and Positive Matrix Factorization (PMF) techniques. PMF was a new statistical tool in the study of particulates in the city of São Paulo. The number of sources identified by these two models was different. The FA technique identified 4 factors, (soil, fuel burning, and 2 factors combining in light and heavy-duty vehicles), whereas PMF identified 6, the same as FA (light and heavier vehicles differentiated) and biomass burning. There was concordance between the two techniques, considering that both found that vehicular emission is the major contribution for concentration. The comparison between the models indicated that PMF model present a better source classification, mainly for the vehicular identification. The PMF technique considers the error of each sample in the analysis, weighting the variables and imposing that all the factors must be positive. This mechanism provides a better characterization of sources linking the results with the physics of the process.

Muitos estudos têm sido desenvolvidos com o intuito de descrever a química da fase gasosa na atmosfera da Região Metropolitana de São Paulo (RMSP). Contudo, o tratamento do material particulado (PM) ainda é feito de forma simplificada em modelos de transporte e químicos atmosféricos, apesar do grande conhecimento já adquirido na caracterização da sua composição elementar e da sua estrutura física. Tendo isso em vista, o objetivo do presente estudo é identificar as principais fontes emissoras do material particulado fino, em especial as fontes veiculares que apresentam muitas dificuldades para sua identificação por não haver medidas de traçadores específicos para os combustíveis utilizados. Neste trabalho foram realizadas amostragens, que duravam 24 horas, próximas a uma avenida de intenso tráfego (Avenida Dr. Arnaldo, na Faculdade de Medicina da Universidade de São Paulo) no período de junho de 2007 a agosto de 2008. Com os dados de composição dessas amostras, a identificação das possíveis fontes foi realizada por modelos receptores; mais especificamente foram utilizados: Análise de Fatores (AF) e Positive Matrix Factorization (PMF), uma nova ferramenta estatística, que ainda não havia sido aplicada no estudo do material particulado em São Paulo. O número de fontes identificadas por essas duas ferramentas estatísticas não foi o mesmo: na AF foram extraídos 4 fatores (solo, queima de óleo combustível e dois fatores que se dividiram, identificando a emissão de veículos leves e pesados não diferenciados), enquanto que o PMF identificou 6 (as mesmas fontes identificadas pela AF, com a diferenciação da emissão veicular (leves e pesados) e ainda a queima de biomassa). Houve concordância entre as duas análises que a maior participação para formação de material particulado fino é da emissão por veículos. A comparação entre os modelos mostrou que os resultados obtidos pelo PMF apresentaram uma melhor divisão das fontes, principalmente na identificação das frotas veiculares. Isso se deve ao fato do PMF considerar na análise o erro de cada concentração medida como um peso para cada variável, além de não permitir a ocorrência de fatores negativos, caracterizando melhor as fontes através da presença desses vínculos físicos. / Several studies have been developed in order to describe the gaseous phase of atmospheric constituents in the Metropolitan Region of Sao Paulo (RMSP). However, the aerosol description remains simplified in chemical models, despite the knowledge acquired in its characterization and composition analyses. Facing these limitations, the objective of this work is to identify the main emission sources of fine particulate matter, specially the vehicular ones that present a lot of difficulties due to the fact that the characteristic trace elements are unknown for these sources. It was used in this work 201 samples collected in 24-hour period each at Dr. Arnaldo Avenue, a large and busy avenue in the city of São Paulo, from June 2007 to August 2008. The source identification was accomplished considering the samples composition and using receptor models: Factor Analysis (FA) and Positive Matrix Factorization (PMF) techniques. PMF was a new statistical tool in the study of particulates in the city of São Paulo. The number of sources identified by these two models was different. The FA technique identified 4 factors, (soil, fuel burning, and 2 factors combining in light and heavy-duty vehicles), whereas PMF identified 6, the same as FA (light and heavier vehicles differentiated) and biomass burning. There was concordance between the two techniques, considering that both found that vehicular emission is the major contribution for concentration. The comparison between the models indicated that PMF model present a better source classification, mainly for the vehicular identification. The PMF technique considers the error of each sample in the analysis, weighting the variables and imposing that all the factors must be positive. This mechanism provides a better characterization of sources linking the results with the physics of the process.

This thesis is based on measurements of aerosol optical and microphysical properties made at inland, coastal and island locations in India. Aerosol vertical distribution measurements have also been made both using surface based and aircraft borne instruments. In addition to these, satellite based measurements (MODIS and OMI) have also been used to estimate regional aerosol radiative forcing over the oceanic regions around India. The measurements at an inland, continental, urban location reveals the large effect of anthropogenic activities on aerosol characteristics at surface and the atmospheric vertical column. A clear seasonality is observed in aerosol optical and microphysical properties as a consequence of modulation by anthropogenic activities and the effect of meteorological parameters like rainfall, winds and boundary layer dynamics. The variability observed at different time scales (from diurnal, weekly, monthly to annual) reveals the importance of anthropogenic and natural processes in modulating the aerosol loading. The estimates of aerosol radiative forcing at surface were as high as ~ 40W m-2. A large discrepancy was observed between the observed and modeled aerosol forcing efficiency (forcing per unit optical depth) at surface. These discrepancies are due to the inadequate representation of aerosol mixing state in models. In addition, the large difference found in the observed forcing between winter and summer could also be influenced due to the presence of elevated aerosols during the summer. Measurements made over coastal and central India shows that a large fraction (75-85%) of aerosol column optical depth was contributed by aerosols located above 1 km. The horizontal gradients were sharp with e-1 scaling distance as small as ~250 km in the well-mixed regions mostly under the influence of local source effects. However, above the atmospheric boundary layer, the gradients were much shallower (~800 to 1200 km). In addition, a large fraction (60-75%) of aerosol was found located above clouds leading to enhanced aerosol absorption. Large spatial gradient in aerosol optical depth and hence radiative impacts between the coastal landmass and the adjacent oceans within a short distance of <300 km (even at an altitude of 3 km) during summer and pre-monsoon is of importance to regional climate. Observations at Minicoy, a remote island in southern Arabian Sea to study the characteristics of transported aerosols reveals variability at daily, weekly, monthly and seasonal time scales associated with changes in precipitation and air mass characteristics. The daily mean Black Carbon (BC) mass mixing ratio varied between as low as ~ 0.2 to 9.0%. The resultant average aerosol atmospheric forcing for the observation period was ~15 W m-2. Trajectory based cluster analysis has shown six distinct advection/transport pathways influencing aerosol characteristics over southern Arabian Sea. The Indo-Gangetic Plain, northern Arabian Sea and west Asia are identified to be the most important source regions having a major impact on aerosols loading over the southern Arabian Sea. The cluster analysis, concentration weighted trajectory (CWT) analysis and the MODIS retrievals show an asymmetry in aerosol characteristics between the Arabian Sea and the Bay of Bengal, with the Arabian Sea characterized by large loading by natural aerosols (eg., dust and sea salt) and the Bay of Bengal characterized by anthropogenic loading (eg., BC). The low value of the BC mass mixing ratio measured at the island (mostly ~ 1 to 1.6%), has major implications for regional radiative forcing. The annually averaged net aerosol atmospheric forcing was as low as ~1.7 W m-2 with highest forcing corresponding to IGP cluster. The single scattering albedo (SSA) which is an important parameter in the estimation of aerosol radiative forcing was retrieved by utilizing a joint OMI-MODIS retrieval methodology. The SSA over the oceanic regions around India shows that the largest absorption (SSA < 0.9) occurs during winter. The largest gradients in AOD and SSA were observed over Arabian Sea during the summer as a result of large dust emissions. The largest forcing observed also was confined to the northern Arabian Sea (~ 37 W m-2) as a result of high aerosol column loading and dust transport. The observed annual mean forcing at Minicoy were comparable to that estimated using satellite measurements, but were much lower than those observed during INDOEX.

To improve the understanding of aerosol composition, sources, and spatial and temporal variations, atmospheric aerosols were characterized in three locations. Ambient aerosols were characterized using 24-hour samples collected from Kathmandu, Nepal (urban), New Hampshire (semi-rural) and Houston (urban). Results are reported in the main chapters. Chamber studies of secondary organic aerosols (SOA) formation from polycyclic aromatic hydrocarbons (PAHs) and the effects of in-situ SOA formation on atmospheric mercury oxidation are described in the appendices. Carbonaceous, ionic, and isotopic species in aerosols from Kathmandu identified local primary emissions, most likely vehicular exhaust as the most important aerosol sources. Carbonaceous aerosols collected in Kathmandu (24.5 μg C m -3 ) were much larger than those in New Hampshire (3.74 μg C m -3 ) during winter. Stable carbon isotope in aerosols of Kathmandu and New Hampshire were similar (Δδ 13 C ∠ 0.5[per thousand]) while stable nitrogen isotope were much lower in aerosols of Kathmandu (Δδ 15 N = 8.3[per thousand]). Aerosols in New Hampshire exhibited a large seasonal variation for carbonaceous aerosols, stable nitrogen isotope, and the aromatic fraction of water-soluble organic carbon (WSOC). Pure aliphatics (H-C) were the dominant functional group in WSOC. Results illustrate the importance of secondary aerosol sources throughout the year, with enhanced importance of primary sources during winter. Stable carbon isotope values suggest a consistent isotopic signature of carbonaceous aerosol sources, while the nitrogen isotope values indicate the variable nitrogenous sources and the strong influence of meteorological parameters (temperature and relative humidity) on nitrogen isotope fractionation. Characteristics of methoxyphenols (lignin macropolymers) in the ambient aerosols are reported for the first time using CuO oxidation method. The study illustrates the use of lignin oxidation products (LOPs) in aerosols as potential tracers of primary biological aerosol particles (PBAP). The methoxyphenols identified soil organic matter and altered woody angiosperms, with minor influence from soft tissues and gymnosperms as the important PBAP sources in mainly coarse particles in Houston atmosphere. Solvent-extracted methoxyphenols (lignin monomers) and anhydrosugars (levoglucosan, mannosan, and galactosan) in aerosols were either absent or very small, suggesting very limited biomass burning influence with any trace-level presence originating from long-range transport.

It is well known that atmospheric aerosols provide the sites for forming cloud droplets, and can affect the Earth's radiation budget through their interactions with clouds. The ability of aerosols to act as cloud condensation nuclei is a strong function of their chemical composition and size. The compositional complexity of aerosol prohibits their explicit treatment in atmospheric models of aerosol-cloud interactions. Nevertheless, the cumulative impact of organics on CCN activity is still required, as carbonaceous material can constitute up to 90% of the total aerosol, 10-70% of which is water soluble. Therefore it is necessary to characterize the water soluble organic carbon fraction by CCN activation, droplet growth kinetics, and surface tension measurements. In this thesis, we investigate the water soluble properties, such as surface tension, solubility, and molecular weight, of laboratory and ambient aerosols and their effect on CCN formation. A mechanism called Curvature Enhanced Solubility is proposed and shown to explain the apparent increased solubility of organics. A new method, called Köhler Theory Analysis, which is completely new, fast, and uses minimal amount of sample was developed to infer the molar volume (or molar mass) of organics. Due to the success of the technique in predicting the molar volume of laboratory samples, it was applied to aerosols collected in Mexico City. Additionally the surface tension, CCN activity, and droplet growth kinetics of these urban polluted aerosols were investigated. Studies performed for the water soluble components showed that the aerosols in Mexico City have surfactants present, can readily become CCN, and have growth similar to ammonium sulfate. Finally, aerosols from three different polluted sources, urban, bovine, and ship emissions, were collected and characterized. The data assembled was used to predict CCN concentrations and access our understanding of the system. From these analyses, it was evident that knowledge of the chemical composition and mixing state of the aerosol is necessary to achieve agreement between observations and predictions. The data obtained in this thesis can be introduced and used as constraints in aerosol-cloud interaction parameterizations developed for global climate models, which could lead to improvements in the indirect effect of aerosols.

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.

Processes at the air-water/ice interface are known to play a very important role in the release of reactive halogen species with atmospheric aerosols serving as catalysts. The ability to make different types of ice with various morphologies, hence, different adsorption and surface properties in vacuum, provide a useful way to probe the catalytic effect of ice in atmospheric reactions. Also, the use of the liquid jet technique provides the rare opportunity to probe liquid samples at the interface; hitherto impossible to investigate with traditional surface science techniques. Studies of reactions on both ice and liquid surfaces at ambient conditions are usually complicated by the rapid desorption and adsorption processes due to the high evaporation rates at the surface. To gain a better understanding and improve modeling of several atmospheric relevant reactions, it is therefore important to develop laboratory techniques that provide an opportunity to investigate non-thermal reactions on both ice and liquid surfaces. Detailed investigation of the interactions of atmospheric relevant molecules (methyl iodide and hydrogen chloride) on water ice at low temperature in UHV conditions has been carried out. These interactions were studied using different techniques such as temperature programmed desorption (TPD), electron stimulated desorption (ESD) and resonance enhanced multiphoton ionization (REMPI). Unlike probing reactions on ice surfaces, investigating air/liquid interfaces present several challenges. This is because traditional surface science techniques require an ultra high vacuum environment to prevent distortion of information due to interference from equilibrium vapor above the liquid surface during data acquisition. The liquid jet technique facilitates the direct study of continually renewed liquid surfaces in high vacuum, thereby preventing the constant changing of the properties and composition of the liquid surface due to the aging process (diffusion of impurities or liquid constituent). A linear time-of-flight mass spectrometer has been used to monitor ion ejection during laser irradiation of liquid jet containing aqueous solutions and pure water. Since these ions are ejected exclusively from the surface of the liquid and the cluster distributions observed are influenced by the local structure, these experiments provide a sensitive probe of the liquid vacuum interface of these solutions. Though the research is fundamental, the results obtained from these investigations indicate how the discontinuity of bulk properties on the surface of both ice and aqueous solutions affects interfacial reactions.

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.

Ensemble simulations of smoke aerosol radiative effects with a regional climate model in the Amazon has been conducted to investigate the radiative effects of aerosols on clouds, rainfall, and circulation from dry to wet season. The results of the ensemble simulations suggest that the radiative effect of the smoke aerosols can reduce daytime surface radiative and sensible fluxes, the depth and instability of the planetary boundary layer (PBL), consequently the clouds in the lower troposphere in early afternoon in the smoke center, where the aerosols optical depth, AOD, exceeds 0.3. The aerosol radiative forcing also appears to weaken moisture transport into the smoke center and increase moisture transport and cloudiness in the region upwind to the smoke center, namely, the northern Amazon. Anomalous wind convergence over the equatorial western Amazon occurs to compensate the anomalous wind divergence in the southern Amazon, leading to an increase of both clouds and rainfall in that region. The increased atmospheric thermodynamic stability in Southern Amazonia also appears to block synoptic cyclonic activities propagated from extratropical South America, leading to an increased synoptic cyclonic activities and rainfall in southern Brazil, Paraguay and northern Argentina. Evidently, the dynamic response of the monsoon circulation plays a major role in determining the pattern of rainfall change induced by the radiative effect of the aerosols.