Estudo da distribuição de tamanho e composição iônica de aerossóis e seus efeitos na capacidade de nuclear gotas de nuvens
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Data
2016-03-04
Autores
Souza, Michele de Lima [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Este trabalho buscou evidências para reconhecer mudanças sazonais nas emissões e consequentes mudanças na composição de aerossóis presentes em uma região subtropical afetada pela queima de biomassa agrícola. Aquisições de dados de distribuição de tamanho e amostragem de aerossol foram feitas próximas ao centro geográfico do estado de São Paulo, no município de Araraquara. A composição iônica das espécies solúveis foram determinadas pela técnica da cromatografia de íons. Diferentes concentrações numéricas da fração mais fina de aerossóis mostraram ser dependentes de condições atmosféricas e, portanto, mostram variações sazonais na formação e crescimento de partículas. A ocorrência preferencial de processos de nucleação homogênea, foram mais pronunciados durante os meses mais chuvosos de verão. Já os processos de nucleação heterogênea, foram favorecidos durante o inverno, quando ocorrem emissões mais intensas da queima de biomassa. A moda de nucleação e a moda de Aitken foram favorecidas no período úmido (verão) e períodos de seca (inverno queima de biomassa), respectivamente. A moda de acumulação mostrou picos no verão e no inverno, o que pode ser explicado pelo crescimento das partículas por efeitos de higroscopicidade e reações heterogêneas concomitantes. Também buscou-se quantificar o possível efeito da presença de aerossóis localizados próximos ao solo nas propriedades das nuvens. Para buscar evidências de interção aerossol-nuvem foram coletados dados a respeito do raio efetivo da gota e da profundidade óptica da nuvem. Estes dados foram obtidos pelo tratamento das medidas realizadas por satélites que orbitam sobre a região de estudo. Os resultados obtidos ao longo de mais de um ano indicaram que as fontes de emissões regionais contribuem para a emissão de aerossóis primários ou formação de aerossóis secundários, que podem influenciar o processo de formação de nuvens. Estes fatos sugerem que as atividades antrópicas sazonais na região podem modificar a composição do aerossol e isto, por sua vez, afetar a formação de nuvens e modificar o ciclo hidrológico, com implicações para os ecossistemas e gestão dos recursos hídricos. Estudos iniciais comparativos sobre a composição iônica de aerossol entre o período de intensa queima da palha da cana-açúcar, em 1999-2001, com os dados do período de implementação da mecanização da colheita, em 2014-2015, mostraram que alguns íons não, necessariamente, reduziram sua concentração, como é o caso do nitrato, espécie secundária, o que implica no favorecimento dos processos de crescimento dos aerossóis. O sulfato, outra espécie secundária, no entanto, teve sua concentração reduzida, inibindo os processos de nucleação. Embora tenha reduzido a queima da palha da cana-de-açúcar no estado de São Paulo, a mesma continuará sendo queimada no restante do país, e seu uso como fonte de energia tem se intensificado, o que torna importante avaliar todos os aspectos relacionados à emissão do aerossol atmosférico e suas implicações ambientais. Portanto, o olhar da ciência sobre o etanol combustível deve ir além do simples balanço entre o carbono emitido e o absorvido.
This study aimed to recognize seasonal changes in emissions and consequent changes in the composition of aerosols present in a subtropical region affected by the agricultural biomass burning. Data acquisition related to the size distribution and aerosol samples were taken near the geographical center of the São Paulo state, in the city of Araraquara. The ionic composition of the soluble species were determined by the ion-chromatography technique. Different numerical concentrations of the finer fraction of aerosols showed to be dependent of the atmospheric conditions and, thus, showed seasonal variations in particle formation and growth. The preferential occurrence of homogeneous nucleation processes were more pronounced during the rainy summer months. But, the heterogeneous nucleation processes were favored during the winter, when there are more intense emissions from biomass burning. The nucleation and Aitken modes were favored in the wet season (summer) and dry periods (winter biomass burning), respectively. Accumulation mode showed peaks in summer and winter, which can be explained by the growth of the particles by the effects of hygroscopicity and concurrent heterogeneous reactions. This work also sought to quantify the possible effect of the presence of aerosols located close to the ground in the clouds properties.To seek evidence of aerosol-cloud interaction, data were collected about the effective radius of the drop and the optical depth of the cloud. These data were obtained from satellites that orbiting over the region of study. The results of the studies over more than one year indicated that the sources of regional emissions contribute to the emission of primary aerosols or formation of secondary aerosols, that can influence the cloud formation process. These facts suggest that the seasonal human activities in the region can alter the composition of the aerosol and this, in turn, affect the formation of clouds and modify the hydrological cycle with implications for ecosystems and water resources management. Comparative initial studies on the ionic composition of the aerosols, from the period of intense sugarcane straw burning, in 1999-2001, with the data of the implementation period of the harvest mechanization, in 2014-2015, showed that some ions do not necessarily reduced their concentration, such as nitrate, secondary species, which implies favoring in aerosols growth processes. The sulfate, other secondary specie, however, was found in reduced concentration, inhibiting the nucleation processes. Despite of the reduction in sugarcane straw burning in São Paulo state, it will continue to be burned in the rest of the country, and its use as energy source have been intensified, which makes it important to evaluate all aspects related to the emission of the atmospheric aerosol and its environmental implications. So, the look of the science on ethanol as fuel must go beyond the simple balance between the emitted and absorbed carbon.
This study aimed to recognize seasonal changes in emissions and consequent changes in the composition of aerosols present in a subtropical region affected by the agricultural biomass burning. Data acquisition related to the size distribution and aerosol samples were taken near the geographical center of the São Paulo state, in the city of Araraquara. The ionic composition of the soluble species were determined by the ion-chromatography technique. Different numerical concentrations of the finer fraction of aerosols showed to be dependent of the atmospheric conditions and, thus, showed seasonal variations in particle formation and growth. The preferential occurrence of homogeneous nucleation processes were more pronounced during the rainy summer months. But, the heterogeneous nucleation processes were favored during the winter, when there are more intense emissions from biomass burning. The nucleation and Aitken modes were favored in the wet season (summer) and dry periods (winter biomass burning), respectively. Accumulation mode showed peaks in summer and winter, which can be explained by the growth of the particles by the effects of hygroscopicity and concurrent heterogeneous reactions. This work also sought to quantify the possible effect of the presence of aerosols located close to the ground in the clouds properties.To seek evidence of aerosol-cloud interaction, data were collected about the effective radius of the drop and the optical depth of the cloud. These data were obtained from satellites that orbiting over the region of study. The results of the studies over more than one year indicated that the sources of regional emissions contribute to the emission of primary aerosols or formation of secondary aerosols, that can influence the cloud formation process. These facts suggest that the seasonal human activities in the region can alter the composition of the aerosol and this, in turn, affect the formation of clouds and modify the hydrological cycle with implications for ecosystems and water resources management. Comparative initial studies on the ionic composition of the aerosols, from the period of intense sugarcane straw burning, in 1999-2001, with the data of the implementation period of the harvest mechanization, in 2014-2015, showed that some ions do not necessarily reduced their concentration, such as nitrate, secondary species, which implies favoring in aerosols growth processes. The sulfate, other secondary specie, however, was found in reduced concentration, inhibiting the nucleation processes. Despite of the reduction in sugarcane straw burning in São Paulo state, it will continue to be burned in the rest of the country, and its use as energy source have been intensified, which makes it important to evaluate all aspects related to the emission of the atmospheric aerosol and its environmental implications. So, the look of the science on ethanol as fuel must go beyond the simple balance between the emitted and absorbed carbon.
Descrição
Palavras-chave
Aerossol, Atmosfera, Distribuição numérica de partículas, Cana-de-açúcar, Aerosol, Atmosphere, Numerical distribution of particles, Sugarcane