Avaliação da composição química e dos processos de transformação gás/partícula do aerossol atmosférico em uma região litorânea sob influência industrial no estado de São Paulo
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Data
2017-02-22
Autores
Francisco, Karen Cristina Almeida [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Este estudo foi desenvolvido com o objetivo de avaliar possíveis impactos de fontes antropogênicas na composição da atmosfera no litoral norte do estado de São Paulo, município de Caraguatatuba. Desde a primeira década do século XXI, este local sofre forte impacto de mudanças nas atividades econômicas impulsionadas pelo projeto de extração de óleo e gás contidos em reservas do pré-sal, pois a região é um dos polos de recebimento e distribuição de petróleo e derivados. Espera-se que o continuo aumento das instalações industriais, trânsito de veículos e embarcações e expansão da área urbana tenham continuidade ainda por muitos anos. Apesar dos possíveis efeitos que essas mudanças podem causar no ambiente não existe nenhum dado sobre composição da atmosfera local e este trabalho apresenta as primeiras medidas de gases ácidos e aerossol atmosférico. As amostragens foram feitas próximo aos limites da área urbana e, de forma concomitante, no alto da Serra do Mar e com isso buscou-se reconhecer possíveis alterações na composição química de gases e aerossol durante os processos de circulação de ar que usualmente ocorrem entre o continente e o oceano e que são influenciados também pelas emissões locais e reações fotoquímicas. Para avaliá-los foi feita caracterização química da atmosfera em relação aos componentes iônicos solúveis do aerossol, aos gases ácidos na fase gasosa e à amônia. Os aerossóis foram coletados por amostrador Hi-Vol, para distribuição do material particulado em seis faixas de tamanho, e por amostrador sequencial do tipo “filter pack”. Este amostrador coleta aerossóis, fazendo sua separação em faixa > 3,5 µm (aerossol grosso) e < 3,5 µm (aerossol fino), gases ácidos e amônia. As determinações químicas das espécies coletadas foram realizadas pela técnica de cromatografia de íons. Como esperado, os processos de emissão por fontes naturais são de grande importância para a formação do aerossol local, destacando-se a abundância do aerossol marinho emitido de forma direta pelo oceano. Porém, o aerossol de origem marinha sofre transformações na atmosfera pela sua interação com espécies ácidas de origem antropogênica. As principais espécies componentes das frações mais grossas foram sódio, cloreto e nitrato, concentrando-se nas partículas com diâmetro entre 3,0 e 7,2 µm. O aerossol mais fino possuía maior composição de amônio, sulfato e nitrato, sugerindo que sua formação ocorre, principalmente, como resultado de reações entre gases ácidos e básicos. Os ácidos HCl e HNO3 foram observados nos dois pontos de amostragem. Já o gás SO2 foi observado apenas próximo ao nível do mar. Observou-se também que a presença do sulfato de origem não marinha aumentou no aerossol, fato que sugere a incorporação no aerossol do enxofre presente originalmente na forma de SO2, tanto no aerossol grosso como fino, durante o transporte para altitude mais elevada. Maior concentração para componentes químicos de origem secundária foram obtidas durante o dia, indicando a dependência de emissões antropogênicas e das reações fotoquímicas para a formação do aerossol. Porém, são necessários estudos complementares para entender como a intensificação de emissões antropogênicas poderá alterar a acidez atmosférica e o papel do aerossol de atuar como núcleo de condensação de nuvem e, consequentemente, afetar os padrões de precipitação da região, além de interferir nos ciclos biogênicos por conta da alteração da composição das espécies depositadas sobre o ecossistema.
This study was developed with the objective of evaluating the possible impacts of anthropic sources on the composition of the atmosphere of a littoral region (Caraguatatuba) located in the state of São Paulo (Brazil). This coastal region is under heavy impact from emissions of various compounds into the atmosphere. The site was chosen as a receiving center for oil and gas extraction products from deepwater reserves known as “pre-sal”. The continued growth of industrial facilities, increased traffic of vehicles and ships, along with expansion of the urban area is expected to increase in the coming years. Despite the possible effects on the environment, there is no data on the composition of the local atmosphere. This work presents the first measurements made in the atmosphere of acid gases and aerosol. The samplings were made close to the urban limits of the city and concomitantly at a sampling point located high in the mountains. Possible changes in the chemical composition of gases and aerosols during air circulation processes, which usually occur between the continent and the ocean, have been studied. These processes are mainly influenced by local emissions, photochemical reactions and air circulation. Samples of formic acid, acetic acid, sulfur dioxide, hydrogen chloride and nitric acid were collected using sequential filtration with cellulose filters treated with sodium carbonate. Ammonia was collected with cellulose filter impregnated with oxalic acid. Samples of particulate matter were collected between in coarse > 3.5 µm and fine < 3.5 µm fractions and using a high-volume sampler operated at a flow rate of 1140 L min-1, onto glass fiber filters. This sampler collected particulates matter using a six-stage (including backup filter) cascade impactor, with aerodynamic cutoffs for the individual stages of 7.2, 3.0, 1.5, 0.95, and 0.49 μm. The soluble ionic components of the aerosol, acid gases and ammonia were quantified using the ion chromatography technique. Fine particles are typically composed of secondary species as nitrates, sulfates and ammonium species. SO2 gas was only observed near sea level. HCl and HNO3 acids were observed at the two sampling points. Higher concentrations of secondary species were obtained during the day, indicating the dependence of anthropic emissions and photochemical reactions. Changes in chemical composition and particle size during transport to higher altitudes have been observed, showing the important role of atmospheric aerosol in maintaining atmospheric neutrality. However, complementary studies are needed to understand how the intensification of anthropogenic emissions could alter atmospheric acidity and even changes in the role of the aerosol to act as a nucleus of cloud condensation and, consequently, affect the precipitation patterns of the region. Other important factor, which needs to be considered, is the role of the deposition of particulate matter on rain forest because increasing the deposition rate can affect the ecology of the forest.
This study was developed with the objective of evaluating the possible impacts of anthropic sources on the composition of the atmosphere of a littoral region (Caraguatatuba) located in the state of São Paulo (Brazil). This coastal region is under heavy impact from emissions of various compounds into the atmosphere. The site was chosen as a receiving center for oil and gas extraction products from deepwater reserves known as “pre-sal”. The continued growth of industrial facilities, increased traffic of vehicles and ships, along with expansion of the urban area is expected to increase in the coming years. Despite the possible effects on the environment, there is no data on the composition of the local atmosphere. This work presents the first measurements made in the atmosphere of acid gases and aerosol. The samplings were made close to the urban limits of the city and concomitantly at a sampling point located high in the mountains. Possible changes in the chemical composition of gases and aerosols during air circulation processes, which usually occur between the continent and the ocean, have been studied. These processes are mainly influenced by local emissions, photochemical reactions and air circulation. Samples of formic acid, acetic acid, sulfur dioxide, hydrogen chloride and nitric acid were collected using sequential filtration with cellulose filters treated with sodium carbonate. Ammonia was collected with cellulose filter impregnated with oxalic acid. Samples of particulate matter were collected between in coarse > 3.5 µm and fine < 3.5 µm fractions and using a high-volume sampler operated at a flow rate of 1140 L min-1, onto glass fiber filters. This sampler collected particulates matter using a six-stage (including backup filter) cascade impactor, with aerodynamic cutoffs for the individual stages of 7.2, 3.0, 1.5, 0.95, and 0.49 μm. The soluble ionic components of the aerosol, acid gases and ammonia were quantified using the ion chromatography technique. Fine particles are typically composed of secondary species as nitrates, sulfates and ammonium species. SO2 gas was only observed near sea level. HCl and HNO3 acids were observed at the two sampling points. Higher concentrations of secondary species were obtained during the day, indicating the dependence of anthropic emissions and photochemical reactions. Changes in chemical composition and particle size during transport to higher altitudes have been observed, showing the important role of atmospheric aerosol in maintaining atmospheric neutrality. However, complementary studies are needed to understand how the intensification of anthropogenic emissions could alter atmospheric acidity and even changes in the role of the aerosol to act as a nucleus of cloud condensation and, consequently, affect the precipitation patterns of the region. Other important factor, which needs to be considered, is the role of the deposition of particulate matter on rain forest because increasing the deposition rate can affect the ecology of the forest.
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Palavras-chave
Química atmosférica, Aerossol, Transformação gás/partícula, Região litorânea, Floresta tropical