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Abstract(s)
O ozono troposférico é um dos poluentes atmosféricos que mais preocupação tem causado ao homem quer pelos efeitos nocivos diretos na saúde das populações, quer pelos prejuízos económicos decorrentes da destruição de culturas agrícolas e florestais, de estruturas construídas e de diversos materiais. As variações das concentrações do ozono da camada superficial da atmosfera são complexas e relativamente rápidas devido a múltiplos fatores tais como as emissões de precursores, a fotoquímica, o transporte horizontal, as interações com a troposfera livre e a deposição.
Com o presente estudo procurou-se avaliar as concentrações de ozono, e de alguns dos seus precursores, registadas em várias estações de monitorização de qualidade do ar nacionais, com vista a identificar os fatores determinantes dos níveis de ozono troposférico prevalecentes nas atmosferas de fundo de Portugal. O estudo apoiou-se numa base de dados de três anos (2009 a 2011) fornecida por 8 estações rurais de fundo, que cumpriram o critério de eficiência de recolha de dados para o período de tempo referido. Os dados foram processados de forma a avaliar os padrões temporais das concentrações de ozono e dos seus precursores azotados e a estabelecer relações entre estes e com outros fatores fisiográficos, como a altitude, a ocupação do solo e a distância à costa.
Os resultados mostram um ciclo diário das concentrações de ozono troposférico com um pico a meio da tarde, com concentrações noturnas mais baixas e uma relação inversa com a evolução diária de NOX, evidenciando a relevância da formação fotoquímica de O3. A nível sazonal, os valores mais elevados surgem na primavera e no Verão.
A avaliação da contribuição local e regional para os níveis de ozono em cada uma das estações permitiu detetar que em algumas regiões é possível reduzir/controlar os níveis de ozono, sendo a estratégia mais eficaz de redução do ozono através do controle das emissões de NOX. Noutras situações, as medidas a adotar têm de ser de carácter mais global dado que resultam de uma componente regional significativa. Foi ainda detetado um padrão espacial relacionado com a variação da altitude e com a distância à costa, que naturalmente têm associados outros fatores de natureza diversa relacionados com a dinâmica da atmosfera e com as emissões de precursores.
Ground level ozone is one of the air pollutants that have caused most concern to humans, either by its direct harmful effects: in human health, in agricultural and forest crops, either by its strong oxidative effect that leads to serious monetary losses by damaging important infrastructures and diverse materials. The variability of ozone concentrations in the surface layer of the atmosphere is complex and relatively fast due to multiple factors such as precursor emissions, photochemistry, horizontal transport, interactions with the free troposphere and deposition. With the present study we sought to evaluate the concentrations of ozone, and some of their precursors, registered in many monitoring stations of national air quality, try to find the determinant factors behind the levels of tropospheric ozone prevailing in the background atmospheres of Portugal. The study relied on a database of three years (2009-2011) provided by eight rural background stations, those meet the criterion of efficiency of data collection for the period of time mentioned. The data were processed to assess the temporal patterns of ozone concentrations and its nitrogen precursors and establish relationships between them and with other physiographic factors such as altitude, land cover and distance from the coast. The results show a daily cycle of tropospheric ozone concentrations with a peak in the afternoon, with lower nighttime concentrations and an inverse relationship with the daily evolution of NOX, demonstrating the relevance of photochemical formation of O3. On the seasonal cycle, the highest values take place in spring and summer. The assessment of local and regional contribution to ozone levels in each of the stations allowed detecting that in some regions it is possible to reduce / control the levels of ozone, and the most effective strategy for reducing ozone is by controlling NOX emissions. In other situations, control measures have to be more global as the result of a significant regional component. It was also detected a spatial pattern related with the change in altitude and distance to the coast, which are naturally associated with other factors of different nature related to the dynamics of the atmosphere and emissions of precursors.
Ground level ozone is one of the air pollutants that have caused most concern to humans, either by its direct harmful effects: in human health, in agricultural and forest crops, either by its strong oxidative effect that leads to serious monetary losses by damaging important infrastructures and diverse materials. The variability of ozone concentrations in the surface layer of the atmosphere is complex and relatively fast due to multiple factors such as precursor emissions, photochemistry, horizontal transport, interactions with the free troposphere and deposition. With the present study we sought to evaluate the concentrations of ozone, and some of their precursors, registered in many monitoring stations of national air quality, try to find the determinant factors behind the levels of tropospheric ozone prevailing in the background atmospheres of Portugal. The study relied on a database of three years (2009-2011) provided by eight rural background stations, those meet the criterion of efficiency of data collection for the period of time mentioned. The data were processed to assess the temporal patterns of ozone concentrations and its nitrogen precursors and establish relationships between them and with other physiographic factors such as altitude, land cover and distance from the coast. The results show a daily cycle of tropospheric ozone concentrations with a peak in the afternoon, with lower nighttime concentrations and an inverse relationship with the daily evolution of NOX, demonstrating the relevance of photochemical formation of O3. On the seasonal cycle, the highest values take place in spring and summer. The assessment of local and regional contribution to ozone levels in each of the stations allowed detecting that in some regions it is possible to reduce / control the levels of ozone, and the most effective strategy for reducing ozone is by controlling NOX emissions. In other situations, control measures have to be more global as the result of a significant regional component. It was also detected a spatial pattern related with the change in altitude and distance to the coast, which are naturally associated with other factors of different nature related to the dynamics of the atmosphere and emissions of precursors.