Browsing by Author "Carvalho, Ana Cristina"
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- Can artificial neural networks be used to predict the origin of ozone episodes?Publication . Fontes, Tânia; Silva, Luís; Silva, Márcia; Barros, Nelson; Carvalho, Ana CristinaTropospheric ozone is a secondary pollutant having a negative impact on health and environment. To control and minimize such impact the European Community established regulations to promote a clean air all over Europe. However, when an episode is related with natural mechanisms as Stratosphere–Troposphere Exchanges (STE), the benefits of an action plan to minimize precursor emissions are inefficient. Therefore, this work aims to develop a tool to identify the sources of ozone episodes in order to minimize misclassification and thus avoid the implementation of inappropriate air quality plans. For this purpose, an artificial neural network model – the Multilayer Perceptron – is used as a binary classifier of the source of an ozone episode. Long data series, between 2001 and 2010, considering the ozone precursors, 7 Be activity and meteorological conditions were used. With this model, 2–7% of a mean error was achieved, which is considered as a good generalization. Accuracy measures for imbalanced data are also discussed. The MCC values show a good performance of the model (0.65–0.92). Precision and F1-measure indicate that the model specifies a little better the rare class. Thus, the results demonstrate that such a tool can be used to help authorities in the management of ozone, namely when its thresholds are exceeded due natural causes, as the above mentioned STE. Therefore, the resources used to implement an action plan to minimize ozone precursors could be better managed avoiding the implementation of inappropriate measures.
- Learning from 24 years of ozone data in PortugalPublication . Barros, Nelson; Silva, M.P.; Fontes, Tânia; Manso, M. Conceição; Carvalho, Ana CristinaOzone (O3) is a secondary pollutant mainly produced in the troposphere by photochemical reactions with high impact on human health. In this work hourly average O3 concentrations from the Portuguese air quality network collected during 24 years (1988–2011) were analysed. The background time series were assessed by environment type (urban, suburban and rural) and considering several criteria: the annual mean O3 concentration, the Directive 2008/50/EC O3 long-term objective and the 2005 WHO Guideline for protection of human health and, finally, the hourly information threshold exceedances. The trend of annual mean O3 concentration data and the maximum daily eight-hour mean ozone concentration data were both annually compared using an one-way ANOVA followed by a Tamhane post-hoc comparison test. In both series, although of an instable trend, a tendency for an increase of the mean O3 concentrations was found. On the other hand, after 2006, for all stations types, the normalized number of exceedances for public O3 information are significantly decreasing (p<0.05). In this paper, the O3 trend will be analyzed and discussed, contributing to improve knowledge of long time series of O3 concentrations in Portugal.
- Ozone deposition modelling in a portuguese coastal zonePublication . Valinhas, Maria José; Borrego, Carlos; Barros, Nelson; Carvalho, Ana CristinaThe deposition of pollutants from the atmosphere to ecosystems is the cause of some present environmental problems: acidification, eutrophication and, indirectly, ground level ozone. Related with these issues is the critical loads/levels concept, widely accepted in Europe as basis for pollution control strategies. The knowledge of atmospheric pollutants deposition on ecosystems is needed to setup this methodology. This paper presents the parameterisation done in the deposition module of the system of models MAR IV which is adequate to simulate the transport, dispersion and removal of pollutants, including ozone production for mesoscale application. The ozone surface resistance (Rc) pararneterisation was applied to Lisbon region and the modelk performance was assessed with ozone deposition experimental data observed in the study area during the fieldwork LisbEx 97. The influence of parameterisation became evident with the good fit between modelled results and measured data. Based on an empirical method described by the Stockholm Environmental Institute report a Critical Load map, for non-forested areas, was calculated for Pomgal. The methodology is based on the kind of soil and its buffer capacity to acid compounds, The results show that around 70°/0of the country is in sensitive areas reinforcing the need for the application of this concept.
- Stratozon: o ozono estratosférico na baixa troposfera sobre PortugalPublication . Barros, Nelson; Borrego, Carlos; Fontes, Tânia; Carvalho, Ana CristinaSupported by Science and Technology Foundation, the STRATOZON project is a 2 years national project and is being developed by Fernando Pessoa and Aveiro Universities, in collaboration with the Meteorological Institute and the Environmental Institute. The main scope of STRATOZON project is to justify non-photochemical ozone episodes, and such, episodes that cannot be controlled by local/regional management of its precursors emissions. At the end, it will be produced a document with guidelines to the Environmental Institute about this subject. Financiado pela Fundação para a Ciência e a Tecnologia, o projecto STRATOZON: O ozono estratosférico na baixa troposfera sobre Portugal, é um projecto nacional, que têm duração de 2 anos (2002-2004), e está a ser desenvolvido pela Universidade Fernando Pessoa e pela Universidade de Aveiro, em colaboração com o Instituto de Meteorologia e o Instituto do Ambiente. O projecto STRATOZON tem como objectivo genérico justificar os episódios de ozono de origem não fotoquímica e, como tal, não passíveis de qualquer controlo local/regional de emissões dos seus precursores. No final será feito um documento contendo directrizes para o Instituto do Ambiente sobre esta matéria.
- A winter ozone episode over PortugalPublication . Carvalho, Ana Cristina; Moreira, Nuno; Leitão, Paula; Fontes, Tânia; Barros, Nelson; Borrego, Carlos