O objetivo desse trabalho foi estudar a relação entre profundidade óptica de aerossóis (AOD), obtida por sensoriamento remoto, e a concentração de material particulado (MP10 e MP2,5) medida próximo à superfície sobre a Região Metropolitana de São Paulo (RMSP). A profundidade óptica foi derivada a partir de medidas de radiâncias fornecidas pelos sensores MODIS. Estes sensores estão posicionados a bordo dos satélites EOS-TERRA e EOS-AQUA, operados pela NASA. As concentrações de MP10 e MP2,5 foram obtidas nas estações da rede operacional da CETESB. Foram feitos alguns estudos de caso considerando diferentes situações atmosféricas, aos quais se aplicou a metodologia proposta por Castanho (2005) que busca reduzir as incertezas na determinação da profundidade óptica derivada do MODIS e identificar qual o modelo de aerossol é mais adequado para aplicação em estudos de qualidade do ar. Os valores de AOD calculados para as diferentes situações foram comparados com aqueles obtidos pela AERONET e com as concentrações anteriormente citadas, buscando uma validação dos mesmos. Valores médios de AOD foram calculados para áreas de 10 km x 10 km ao redor das estações de monitoramento do MP. Testes foram realizados para verificar os efeitos de sazonalidade, da quantidade de água na coluna atmosférica, da resposta da AOD por faixas de concentração de MP10, da geometria do sensor, da presença de nuvens e da presença de aerossol acima da Camada de Mistura (CM). Os resultados foram apresentados por estações com o objetivo de se visualizar diferentes condições sobre a região estudada. Alguns dos fatores relevantes observados durante a comparação entre a concentração de MP10 e a AOD foram: a influência do período do ano e da quantidade de água na coluna atmosférica. A geometria do sensor foi fator determinante para melhora das correlações, quando limitado o ângulo de espalhamento em 140°. Situações em que há ausência de nuvens, identificadas através de imagens do MODIS no visível, também apresentaram melhores resultados. Outro fator de extrema importância foi a estrutura vertical da CM. Através de medidas obtidas de um LIDAR foi verificado que a presença de aerossóis acima da CM, a qual é determinada principalmente pelas condições atmosféricas, é determinante para as correlações entre AOD e o MP. / The main purpose of this work was to study the relationship between the Aerosol Optical Depth (AOD), obtained by remote sensing, and the particulate material concentration (PM10 and PM2.5), near to the surface over the Metropolitan Area of Sao Paulo (MASP). The Aerosol Optical Depth was retrieved based on reflectance measurements provided by MODIS sensors. These sensors are carried aboard EOS-TERRA and EOS-AQUA satellites, which are operated by NASA. The PM10 and PM2.5 concentrations were obtained in the CETESB operational network. Case studies were performed, considering several atmospheric conditions, applying the methodology proposed by CASTANHO (2005), designed both to reduce the uncertainty in the determination of the MODIS derived Optical Depth and to identify which aerosol model is more appropriated for air quality studies. Some derived results were compared with AERONET data and with the previously mentioned concentrations as a cross-check test. Mean AOD values were calculated using 10 km x 10 km area ground around PM monitoring stations. Tests were performed to estimate the effects of seasonality, atmospheric column water content, AOD response to PM10 concentration, sensor geometry, clouds and aerosol concentration above the Mixing Layer (ML). To stress the different conditions of the studied region, the results were presented considering each station. Some of the relevant observed factors in the PM10 concentration and AOD comparison were the year period influence and the atmospheric column water content. The sensor geometry was an important factor to the improvement of the obtained correlations when the scattering angle was bounded to 140°. Cloudless situations, identified by MODIS true color images, also improved the results. Another important factor was the Mixing Layer vertical structure. Using LIDAR measurements it was verified that the presence of aerosols above the ML, which is determined mainly by atmospheric conditions, is crucial for the correlations between AOD and PM.

Spatial distribution of diurnal variations of aerosol properties in South Korea, both long term and short term, is studied by using 9 AERONET sites from 1999 to 2017 for long-term averages and from an additional 10 sites during the KORUS-AQ field campaign. The extent to which WRF-Chem model and the GOCI satellite retrieval can describe these variations is also analyzed. In daily average, Aerosol Optical Depth (AOD) at 550 nm is 0.386 and shows a diurnal variation of +20 to -30% in inland sites, respectively larger than the counterparts of 0.308 and ± 20% in coastal sites. Both the inland and coastal sites have their diurnal variation peaks in the early morning and in the evening with noontime and early afternoon valleys. In contrast, Angstrom exponent values in all sites are between 1.2 and 1.4 with the exception of the inland rural sites having smaller values near 1.0 during the early morning hours. All inland sites experience a pronounced increase of Angström Exponent from morning to evening, reflecting overall decrease of particle size in daytime. To statistically obtain the climatology of diurnal variation of AOD, a minimum of requirement of ~2 years of observation is needed in coastal rural sites, twice more than the urban sites, which suggests that diurnal variation of AOD in urban setting is distinct and persistent. AERONET, GOCI, WRF-Chem, and observed PM2.5 data consistently show dual peaks for both AOD and PM2.5, one at ~ 10 KST and another ~14 KST. While Korean GOCI satellite is able to consistently capture the diurnal variation of AOD, WRF-Chem clearly has the deficiency to describe the relatively change of peaks and variations between the morning and afternoon, suggesting further studies for the diurnal profile of emissions. Overall, the relative small diurnal variation of PM2.5 is in high contrast with large AOD diurnal variation, which suggests the need to use AOD from geostationary satellites for constrain either modeling or analysis of surface PM2.5 for air quality application.

Σύμφωνα με την πρόσφατη έκθεση της Διακυβερνητικής Επιτροπής για την Κλιματική Αλλαγή (Intergovernmental Panel on Climate Change, IPCC), η επίδραση των αιωρούμενων σωματιδίων στο ενεργειακό ισοζύγιο της ατμόσφαιρας κρίνεται ως ιδιαίτερα σημαντική. Αυτό οφείλεται στα φαινόμενα σκέδασης και απορρόφησης που προκαλούν στην ηλιακή ακτινοβολία κατά τη διάδοσή της στην ατμόσφαιρα και στην επίδρασή τους στις ιδιότητες των νεφών. Στην παρούσα διπλωματική εργασία έγινε μια προσπάθεια ανάλυσης των δεδομένων που έχουμε στη διάθεσή μας από το διεθνές δίκτυο επίγειων σταθμών AERONET που λειτουργεί υπό την αιγίδα της NASA και από το δορυφορικό όργανο MODIS (Moderate Resolution Imaging Spectoradiometer) που βρίσκεται στους δορυφόρους πολικής τροχιάς Terra και Aqua με σκοπό την εξαγωγή συμπερασμάτων σχετικά με τη χωρική και εποχική διακύμανση των οπτικών ιδιοτήτων των αιωρούμενων σωματιδίων και σχετικά με την αντιπροσωπευτικότητα των επιγείων σταθμών σε σύγκριση με το MODIS των δορυφόρων Terra και Aqua. Η μελέτη έγινε για τρεις αστικές περιοχές της Ελλάδας, την Αθήνα, το Ηράκλειο και τη Θεσσαλονίκη, όπου υπάρχουν επίγειοι σταθμοί και δορυφορικά δεδομένα από τη γύρω περιοχή με χωρική ανάλυση 10x10 km2. Η δομή της εργασίας έχει ως εξής: Στο πρώτο κεφάλαιο, δίνεται ο ορισμός των αιωρούμενων σωματιδίων, αναλύεται η χημική τους σύσταση, οι μορφές στις οποίες απαντώνται στην ατμόσφαιρα, οι πηγές προέλευσής τους, η κατανομή τους σε διάφορες κατηγορίες με διαφορετικά κριτήρια όπως επίσης και οι μηχανισμοί απομάκρυνσής τους από την ατμόσφαιρα. Στο δεύτερο κεφάλαιο, αναλύονται οι φυσικές ιδιότητες των αιωρούμενων σωματιδίων και οι μηχανισμοί επίδρασής τους στην ακτινοβολία. Ιδιαίτερη σημασία δίνεται στον εκθέτη Angstrom και στο οπτικό βάθος των αιρούμενων σωματιδίων καθώς είναι το αντικείμενο της μελέτης μας. Στη συνέχεια, στο τρίτο κεφάλαιο, γίνεται μια αναφορά στις επιδράσεις των αιωρούμενων σωματιδίων όσον αφορά στο κλίμα και στο ενεργειακό ισοζύγιο καθώς επίσης στην υγεία και στην ορατότητα. Στο τέταρτο κεφάλαιο, γίνεται αρχικά μια αναφορά στο διεθνές δίκτυο επιγείων σταθμών AERONET και στο φασματο-ραδιόμετρο MODIS από όπου έχουμε τις μετρήσεις μας. Έπειτα, περιγράφεται το πρώτο στάδιο της επεξεργασίας των μετρήσεών μας, το οποίο περιλαμβάνει τη σχηματική σύγκριση των μετρήσεων που έχουμε από τους επιγείους σταθμούς και τους δορυφόρους. Περνώντας στο πέμπτο κεφάλαιο της εργασίας, αναλύεται η μέθοδος με την οποία γίνεται η χωρική ομαδοποίηση των μετρήσεων από τους δορυφόρους και στη συνέχεια ακολουθεί το δεύτερο στάδιο της επεξεργασίας των μετρήσεων κατά το οποίο αναπαρίστανται τα σχήματα ομαδοποίησης των δορυφορικών μετρήσεων με διάφορα κριτήρια. Τέλος, στο έκτο κεφάλαιο, σχολιάζονται τα τελικά αποτελέσματα και εξάγονται τα αντίστοιχα συμπεράσματα για την εποχική και χωρική διακύμανση των αιωρούμενων σωματιδίων, αλλά και την αντιπροσωπευτικότητα των επιγείων σταθμών σε σχέση με τους δορυφόρους. / According to a recent report by the Intergovernmental Panel on Climate Change (IPCC), the effect of suspended particles in the energy balance of the atmosphere is considered as very important. This is due to scattering and absorption phenomena caused by solar radiation during propagation in the atmosphere and their effect on the properties of clouds. This thesis was an attempt to analyze the available data by the international network of ground aerosol stations AERONET and the satellite instrument MODIS (Moderate Resolution Imaging Spectoradiometer) on-board the Terra and Aqua satellites and investigate the spatial and temporal variation of the optical properties of aerosols and the representativeness of the earth stations compared to the MODIS satellites Terra and Aqua. The study was conducted in three urban areas of Greece, Athens, Heraklion and Thessaloniki, where there are data from ground-based stations and satellite estimations from the surrounding area with a spatial resolution of 10x10 km2. The structure of this thesis is as follows: The first chapter begins with a definition of aerosols, the analysis of their chemical composition, the forms with which aerosols occur in the atmosphere, the sources of their origin, their distribution in categories with different criteria as well as the mechanisms for their removal from the atmosphere. The second chapter analyzes the physical properties of aerosols and mechanisms of their influence on radiation. Particular attention is given to the Angstrom exponent and the optical depth of aerosols, parameters that lie within the object of our study. In the third chapter, there is a description of the aerosol effects on climate and the energy balance as well as health and visibility. In the fourth chapter, there is firstly a description of the international AERONET network of ground stations and the MODIS spectral radiometer. Then, we describe the first stage of our measurement analysis, which includes the schematic comparison of measurements derived from ground stations and satellites. In the fifth chapter, we analyze the method for the spatial clustering of measurements from satellites and the clustering shapes of satellite measurements using different criteria. Finally, in the sixth chapter, we discuss the results and conclusions corresponding to the seasonal and spatial variability of aerosols, and the representativeness of the ground measurements in comparison with the satellite estimations.

O objetivo desse trabalho foi estudar a relação entre profundidade óptica de aerossóis (AOD), obtida por sensoriamento remoto, e a concentração de material particulado (MP10 e MP2,5) medida próximo à superfície sobre a Região Metropolitana de São Paulo (RMSP). A profundidade óptica foi derivada a partir de medidas de radiâncias fornecidas pelos sensores MODIS. Estes sensores estão posicionados a bordo dos satélites EOS-TERRA e EOS-AQUA, operados pela NASA. As concentrações de MP10 e MP2,5 foram obtidas nas estações da rede operacional da CETESB. Foram feitos alguns estudos de caso considerando diferentes situações atmosféricas, aos quais se aplicou a metodologia proposta por Castanho (2005) que busca reduzir as incertezas na determinação da profundidade óptica derivada do MODIS e identificar qual o modelo de aerossol é mais adequado para aplicação em estudos de qualidade do ar. Os valores de AOD calculados para as diferentes situações foram comparados com aqueles obtidos pela AERONET e com as concentrações anteriormente citadas, buscando uma validação dos mesmos. Valores médios de AOD foram calculados para áreas de 10 km x 10 km ao redor das estações de monitoramento do MP. Testes foram realizados para verificar os efeitos de sazonalidade, da quantidade de água na coluna atmosférica, da resposta da AOD por faixas de concentração de MP10, da geometria do sensor, da presença de nuvens e da presença de aerossol acima da Camada de Mistura (CM). Os resultados foram apresentados por estações com o objetivo de se visualizar diferentes condições sobre a região estudada. Alguns dos fatores relevantes observados durante a comparação entre a concentração de MP10 e a AOD foram: a influência do período do ano e da quantidade de água na coluna atmosférica. A geometria do sensor foi fator determinante para melhora das correlações, quando limitado o ângulo de espalhamento em 140°. Situações em que há ausência de nuvens, identificadas através de imagens do MODIS no visível, também apresentaram melhores resultados. Outro fator de extrema importância foi a estrutura vertical da CM. Através de medidas obtidas de um LIDAR foi verificado que a presença de aerossóis acima da CM, a qual é determinada principalmente pelas condições atmosféricas, é determinante para as correlações entre AOD e o MP. / The main purpose of this work was to study the relationship between the Aerosol Optical Depth (AOD), obtained by remote sensing, and the particulate material concentration (PM10 and PM2.5), near to the surface over the Metropolitan Area of Sao Paulo (MASP). The Aerosol Optical Depth was retrieved based on reflectance measurements provided by MODIS sensors. These sensors are carried aboard EOS-TERRA and EOS-AQUA satellites, which are operated by NASA. The PM10 and PM2.5 concentrations were obtained in the CETESB operational network. Case studies were performed, considering several atmospheric conditions, applying the methodology proposed by CASTANHO (2005), designed both to reduce the uncertainty in the determination of the MODIS derived Optical Depth and to identify which aerosol model is more appropriated for air quality studies. Some derived results were compared with AERONET data and with the previously mentioned concentrations as a cross-check test. Mean AOD values were calculated using 10 km x 10 km area ground around PM monitoring stations. Tests were performed to estimate the effects of seasonality, atmospheric column water content, AOD response to PM10 concentration, sensor geometry, clouds and aerosol concentration above the Mixing Layer (ML). To stress the different conditions of the studied region, the results were presented considering each station. Some of the relevant observed factors in the PM10 concentration and AOD comparison were the year period influence and the atmospheric column water content. The sensor geometry was an important factor to the improvement of the obtained correlations when the scattering angle was bounded to 140°. Cloudless situations, identified by MODIS true color images, also improved the results. Another important factor was the Mixing Layer vertical structure. Using LIDAR measurements it was verified that the presence of aerosols above the ML, which is determined mainly by atmospheric conditions, is crucial for the correlations between AOD and PM.

Abstract : This is a study concerning comparisons between the Dubovik Aerosol optical depth (AOD) retrievals from AEROCAN (ARONET) stations and AOD estimates from simulations provided by a chemical transport model (GEOS-Chem : Goddard Earth Observing System Chemistry). The AOD products associated with the Dubovik product are divided into total, fine and coarse mode components. The retrieval period is from January 2009 to January 2013 for 5 Arctic stations (Barrow, Alaska; Resolute Bay, Nunavut; 0PAL and PEARL (Eureka), Nunavut; and Thule, Greenland). We also employed AOD retrievals from 10 other mid-latitude Canadian stations for comparisons with the Arctic stations. The results of our investigation were submitted to Atmosphere-Ocean. To briefly summarize those results, the model generally but not always tended to underestimate the (monthly) averaged AOD and its components. We found that the subdivision into fine and coarse mode components could provide unique signatures of particular events (Asian dust) and that the means of characterizing the statistics (log-normal frequency distributions versus normal distributions) was an attribute that was common to both the retrievals and the model. / Résumé : Cette étude compare des épaisseurs optiques d’aérosols (AOD) à 5 stations arctiques d’AEROCAN (AERONET), obtenues d’une part à l’aide de l’algorithme d'inversion de Dubovik appliqué à des mesures in situ, et d’autre part du modèle de transport chimique (GEOS-Chem : Goddard Earth Observing Système Chemistry). Les produits d’AOD associés à l’algorithme d’inversion sont divisés en composantes totales, fines et grossières. Pour chacune des 5 stations (Barrow, Alaska, Resolute Bay, au Nunavut, 0PAL et PEARL (Eureka), Nunavut, et Thulé, au Groenland), la période de récupération est de janvier 2009 à janvier 2013. Nous avons également utilisé les mesureurs d’AOD de dix autres stations canadiennes de latitudes moyennes, à des fins de comparaison. Les résultats de l’étude ont été soumis à la revue Atmosphere-Ocean. Pour résumer brièvement ces résultats, le modèle a généralement, mais pas toujours, eu tendance à sous-estimer l'AOD moyenne et de ses composantes. Nous avons constaté que la subdivision en composantes fine et grossière pourrait fournir des signatures uniques d'événements particuliers (poussière asiatique) et que les moyens de caractériser des statistiques (les distributions de fréquence log-normale versus les distributions normales) était un attribut qui était commun aux deux les mesureurs et le modèle.

No description available.

Earth's radiation budget is directly influenced by aerosols through the absorption of solar radiation and subsequent heating of the atmosphere. Aerosols modulate the hydrological cycle indirectly by modifying cloud properties, precipitation and ocean heat storage. In addition, polluting aerosols impose health risks in local, regional and global scales. In spite of recent advances in the study of aerosols variability, uncertainty in their spatial and temporal distributions still presents a challenge in the understanding of climate variability. For example, aerosol loading varies not only from year to year but also on higher frequency intraseasonal time scales producing strong variability on local and regional scales. An assessment of the impact of aerosol variability requires long period measurements of aerosols at both regional and global scales. The present dissertation compiles a large database of remotely sensed aerosol loading in order to analyze its spatio-temporal variability, and how this load interacts with different variables that characterize the dynamic and thermodynamic states of the environment. Aerosol Index (AI) and Aerosol Optical Depth (AOD) were used as measures of the atmospheric aerosol load. In addition, atmospheric and oceanic satellite observations, and reanalysis datasets is used in the analysis to investigate aerosol-environment interactions. A diagnostic study is conducted to produce global and regional aerosol satellite climatologies, and to analyze and compare the validity of aerosol retrievals. We find similarities and differences between the aerosol distributions over various regions of the globe when comparing the different satellite retrievals. A nonparametric approach is also used to examine the spatial distribution of the recent trends in aerosol concentration. A significant positive trend was found over the Middle East, Arabian Sea and South Asian regions strongly influenced by increases in dust events. Spectral and composite analyses of surface temperature, atmospheric wind, geopotential height, outgoing longwave radiation, water vapor and precipitation together with the climatology of aerosols provide insight on how the variables interact. Different modes of variability, especially in intraseasonal time scales appear as strong modulators of the aerosol distribution. In particular, we investigate how two modes of variability related to the westward propagating synoptic African Easterly Waves of the Tropical Atlantic Ocean affect the horizontal and vertical structure of the environment. The statistical significance of these two modes is tested with the use of two different spectral techniques. The pattern of propagation of aerosol load shows good correspondence with the progression of the atmospheric and oceanic synoptic conditions suitable for dust mobilization over the Atlantic Ocean. We present extensions to previous studies related with dust variability over the Atlantic region by evaluating the performance of the long period satellite aerosol retrievals in determining modes of aerosol variability. Results of the covariability between aerosols-environment motivate the use of statistical regression models to test the significance of the forecasting skill of daily AOD time series. The regression models are calibrated using atmospheric variables as predictors from the reanalysis variables. The results show poor forecasting skill with significant error growing after the 3rd day of the prediction. It is hypothesized that the simplicity of linear models results in an inability to provide a useful forecast.

Indiana University-Purdue University Indianapolis (IUPUI) / Objective: "The purpose of this research is: Study the use of Moderate Resolution Imaging Spectroradiometer (MODIS) data in retrieving the aerosol optical depth (AOD) over Indiana State at high resolution of 500 meters. Examine the potential of using the resulted AOD data as an indicator of particulate air pollution by comparing the satellite derived AOD data with the ground measurements (provided from the continuous air monitors available over the study area). If an association should be found, AOD data would be used to map particulate matter (PM) concentration. Assess current and future ambient concentrations of air pollutants in the State of Indiana using the AOD."

To identify the long-term trend of particle size variation, we analyzed aerosol optical depth (AOD, τ) separated as dust (τD) and coarse-(τPC) and fine-pollution particles (τPF) depending on emission sources and size. Ångström exponent values are also identified separately as total and fine-mode particles (αT and αPF). We checked these trends in various ways; (1) first-order linear regression analysis of the annual average values, (2) percent variation using the slope of linear regression method, and (3) a reliability analysis using the Mann–Kendall (MK) test. We selected 17 AERONET sun/sky radiometer sites classified into six regions, i.e., Europe, North Africa, the Middle East, India, Southeast Asia, and Northeast Asia. Although there were regional differences, τ decreased in Europe and Asian regions and increased in the Middle East, India, and North Africa. Values of τPC and τPF, show that aerosol loading caused by non-dust aerosols decreased in Europe and Asia and increased in India. In particular, τPF considerably decreased in Europe and Northeast Asia (95% confidential levels in MK-test), and τPC decreased in Northeast Asia (Z-values for Seoul and Osaka are −2.955 and −2.306, respectively, statistically significant if |z| ≥ 1.96). The decrease in τPC seems to be because of the reduction of primary and anthropogenic emissions from regulation by air quality policies. The meaningful result in this paper is that the particle size became smaller, as seen by values of αT that decreased by −3.30 to −30.47% in Europe, North Africa, and the Middle East because αT provides information on the particle size. Particle size on average became smaller over India and Asian regions considered in our study due to the decrease in coarse particles. In particular, an increase of αPF in most areas shows the probability that the average particle size of fine-mode aerosols became smaller in recent years. We presumed the cause of the increase in αT is because relatively large-sized fine-mode particles were eliminated due to air quality policies.

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 0,20<POA<=0,60 no canal 415nm com o aumento da umidade relativa. Acredita-se que este grupo tenha predominância de aerossóis de fontes locais. As medidas de longo prazo permitiram também caracterizar, em conjunto com estimativas espaciais de POA pelo sensor Moderate Resolution Imaging Spectroradiometer (MODIS) a bordo do satélite Terra, a influência do transporte de aerossóis de queimadas da região amazônica e do Brasil central em São Paulo, na série de dados analisados. Estes eventos contribuem para o aumento significativo da POA sobre a região metropolitana e trazem partículas ligeiramente menores que as emitidas por fontes locais. / The 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<AOD<=0.60, in the channel 415 nm, with increasing relative humidity. It is believed that this group has predominance of aerosols from local sources. Long term measurements also helped to characterize, together with spatial estimates of AOD by the Moderate Resolution Imaging Spectroradiometer (MODIS) on board the Terra satellite, the influence of the transport of aerosol particles from biomass burning from the Amazon region to São Paulo. It was observed that these events contribute to significant increase in AOD on the metropolitan region and bring slightly smaller particles than the emitted by local sources.