Characterization of the radiative impact of aerosols on CO₂ and energy fluxes in the Amazon deforestation arch using artificial neural networks

In vegetation canopies with complex architectures, diffuse solar radiation can enhance carbon assimilation through photosynthesis because isotropic light is able to reach deeper layers of the canopy. Although this effect has been studied in the past decade, the mechanisms and impacts of this enhancement over South America remain poorly understood. Over the Amazon deforestation arch large amounts of aerosols are released into the atmosphere due to biomass burning, which provides an ideal scenario for further investigation of this phenomenon in the presence of canopies with complex architecture. In this paper, the relation of aerosol optical depth and surface fluxes of mass and energy are evaluated over three study sites with artificial neural networks and radiative transfer modeling. Results indicate a significant effect of the aerosol on the flux of carbon dioxide between the vegetation and the atmosphere, as well as on energy exchange, including that surface fluxes are sensitive to second-order radiative impacts of aerosols on temperature, humidity, and friction velocity. CO₂ exchanges increased in the presence of aerosol in up to 55 % in sites with complex canopy architecture. A decrease of approximately 12 % was observed for a site with shorter vegetation. Energy fluxes were negatively impacted by aerosols over all study sites

Estudo da variabilidade espacial e temporal da profundidade óptica do aerossol obtida com o MODIS sobre a região amazônica

Realizou-se um estudo da variabilidade temporal da profundidade óptica do aerossol (AOD) e sua homogeneidade espacial com o objetivo de descrever e quantificá-la em cinco pontos da região amazônica, dos quais quatro sofrem com emissões de queimadas, utilizando uma longa série de dados. Os dados foram obtidos a partir do sensor MODIS (Moderate Resolution Imaging Spectroradiometer), a bordo dos satélites Terra e Aqua, entre 2000 e 2011. Foi realizada análise da homogeneidade espacial dos valores de AOD e de sua variabilidade diurna, assim como foram calculados os valores médios anuais e mensais de AOD e definidos períodos de altos valores para os sítios do arco do desmatamento. Observou-se que a AOD variou pouco com o aumento da área, indicando que as camadas de aerossol são bastante misturadas. As flutuações nas médias anuais de AOD apresentaram comportamento semelhante nos sítios do arco do desmatamento, sendo que Manaus apresentou influências desse padrão em anos mais secos e São Gabriel da Cachoeira apresentou apenas valores baixos (AOD entre 0,1-0,2). O número de dias com AOD maior no período da tarde é consideravelmente maior, provavelmente pelas queimadas ocorrerem principalmente à tarde. Os períodos de altos valores (AOD entre 1-3) começaram no fim da estação seca e terminaram no início da estação chuvosa, sendo a duração estimada entre 69 e 79 dias

Desempenho de modelos radiativos na avaliacao de irradiancias em presença de aerossol de queimadas

A inclusão de processos de interação entre a radiação solar e partículas de aerossol tem sido considerada como relevante no aperfeiçoamento dos modelos meteorológicos mais comumente utilizados para previsão de tempo e clima no mundo. Modelos meteorológicos empregados na previsão de condições ambientais na América do Sul são particularmente sensíveis a uma descrição realista da interação entre a radiação solar e o aerossol de queimadas. Este estudo compara observações de irradiância solar à superfície em presença de aerossol de queimadas e seus respectivos valores teóricos obtidos mediante diferentes modelos radiativos. As observações em questão foram efetuadas em setembro e outubro de 2002 nas proximidades de Ouro Preto dOeste (Rondônia), durante a realização do experimento RACCI/SMOCC. Alguns dos modelos radiativos em questão foram concebidos para emprego em modelos meteorológicos e portanto envolvem aproximações mais severas quanto à avaliação dos efeitos de espalhamento e de absorção de radiação solar por uma população de partículas em suspensão na atmosfera. Um segundo grupo de modelos radiativos considera representações mais sofisticadas com vistas à avaliação destes mesmos efeitos, além de permitir cálculos com maior resolução em comprimento de onda. Os resultados incluem testes de sensibilidade sobre a refletância da superfície, sobre a repartição vertical das partículas de aerossol, e sobre as propriedades ópticas do aerossol de queimadas

Multifilter rotating shadowband radiometer calibration for spectral aerosol optical depth retrievals over Sao Paulo City, Brazil

Multifilter rotating shadowband radiometer (MFRSR) calibration values for aerosol optical depth (AOD) retrievals were determined by means of the general method formulated by Forgan [Appl. Opt. 33, 4841 (1994)] at a polluted urban site. The obtained precision is comparable with the classical method, the Langley plot, applied on clean mountaintops distant of pollution sources. The AOD retrieved over Sao Paulo City with both calibration procedures is compared with the Aerosol Robotic Network data. The observed results are similar, and, except for the shortest wavelength (415 nm), the MFRSR`s AOD is systematically overestimated by similar to 0.03. (c) 2008 Optical Society of America

Fifty-six years of surface solar radiation and sunshine duration over São Paulo, Brazil: 1961–2016

A total of 56 years (1961–2016) of daily surface downward solar irradiation, sunshine duration, diurnal temperature range and the fraction of the sky covered by clouds in the city of São Paulo, Brazil, were analysed. The main purpose was to contribute to the characterization and understanding of the dimming and brightening effects on solar global radiation in this part of South America. As observed in most of the previous studies worldwide, in this study, during the period between 1961 and the early 1980s, a negative trend in surface solar irradiation was detected in São Paulo, characterizing the occurrence of a dimming effect. Sunshine duration and the diurnal temperature range also presented negative trends, in opposition to the positive trend observed in the cloud cover fraction. However, a brightening effect, as observed in western industrialized countries in more recent years, was not observed. Instead, for surface downward irradiation, the negative trend persisted, with a trend of −0.13 MJ m−2 per decade, with a p value of 0.006, for the 56 years of data and in consonance with the cloud cover fraction increasing trend, but not statistically significant, of 0.3 % per decade (p value = 0.198). The trends for sunshine duration and the diurnal temperature range, by contrast, changed signal, as confirmed by a piecewise linear regression model. Some possible causes for the discrepancy are discussed, such as the frequency of fog occurrence, urban heat island effects, horizontal visibility (as a proxy for aerosol loading variability) and greenhouse gas concentration increase. Future studies on the aerosol effect are planned, particularly with higher temporal resolution, as well as modelling studies, to better analyse the contribution of each possible cause.ISSN:1680-7375ISSN:1680-736

The relationship between aerosol particles chemical composition and optical properties to identify the biomass burning contribution to fine particles concentration: a case study for Sao Paulo city, Brazil

The air quality in the Metropolitan Area of Sao Paulo (MASP) is primarily determined by the local pollution source contribution, mainly the vehicular fleet, but there is a concern about the role of remote sources to the fine mode particles (PM2.5) concentration and composition. One of the most important remote sources of atmospheric aerosol is the biomass burning emissions from Sao Paulo state's inland and from the central and north portions of Brazil. This study presents a synergy of different measurements of atmospheric aerosol chemistry and optical properties in the MASP in order to show how they can be used as a tool to identify particles from local and remote sources. For the clear identification of the local and remote source contribution, aerosol properties measurements at surface level were combined with vertical profiles information. Over 15 days in the austral winter of 2012, particulate matter (PM) was collected using a cascade impactor and a Partisol sampler in Sao Paulo City. Mass concentrations were determined by gravimetry, black carbon concentrations by reflectance, and trace element concentrations by X-ray fluorescence. Aerosol optical properties were studied using a multifilter rotating shadowband radiometer (MFRSR), a Lidar system and satellite data. Optical properties, concentrations, size distributions, and elemental composition of atmospheric particles were strongly related and varied according to meteorological conditions. During the sampling period, PM mean mass concentrations were 17.4 +/- 10.1 and 15.3 +/- 6.9 mu g/m(3) for the fine and coarse fractions, respectively. The mean aerosol optical depths at 415 nm and Angstrom exponent (AE) over the whole period were 0.29 +/- 0.14 and 1.35 +/- 0.11, respectively. Lidar ratios reached values of 75 sr. The analyses of the impacts of an event of biomass burning smoke transport to the Sao Paulo city revealed significant changing on local aerosol concentrations and optical parameters. The identification of the source contributions, local and remote, to the fine particles in MASP can be more precisely achieved when particle size composition and distribution, vertical profile of aerosols, and air mass trajectories are analyzed in combination.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Univ Sao Paulo, Sch Arts Sci & Humanities, Rua Arlindo Bettio1000, BR-03828000 Sao Paulo, SP, BrazilUniv Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Dept Ciencias Atmosfer, Rua Matao 1226, BR-05508090 Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Dept Environm Sci, Rua Prof Artur Riedel 275, BR-09972270 Diadema, SP, BrazilIPEN CNEN SP, Nucl & Energy Res Inst, Av Lineu Prestes 2242, BR-05508000 Sao Paulo, SP, BrazilEnvironmental Sciences Department, Universidade Federal de São Paulo (UNIFESP), Rua Prof Artur Riedel 275, BR-09972270, Diadema, SP, BrazilFAPESP: 2008/58104-8FAPESP: 2011/14365-5FAPESP: 2012/24689-5Web of Scienc