FCT (DCEA) - Artigos em Revistas Científicas Internacionais com Arbitragem Científica
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- Intercomparison of two meso-meteorological models applied to the Lisbon regionPublication . Borrego, C.; Coutinho, M.; Barros, NelsonIn this paper two mesoscale meteorological models are applied to the Lisbon region. A special concern is directed to the initial conditions and input parameterization in order to assure that equal simulation constraints were imposed to both models. Results obtained for 4 August 1992 (a typical summer day) are compared to meteorological data acquired in three monitoring stations. Both simulations show similar reactions to the mesoscale forcings that occur in the modelling region. The minor differences found between simulation and reality for the meteorological situation can cause major errors in predicting air quality.
- Impact of road traffic emissions on air quality of the Lisbon regionPublication . Borrego, C.; Tchepel, O.; Barros, Nelson; Miranda, A.I.The main purpose of this paper is to present the study of traffic emissions impact on the Lisbon region air quality. Two approaches of emission data generation with high spatial and temporal resolution are presented and compared. Main roads were processed as line sources and hot on-road emissions were calculated based on daily mean traffic and emission factors distinguished for several road classes and vehicle types. Also, the disaggregation of national CORINAIR inventory has been performed on the basis of statistical information of fuel consumption and population density. The comparison of emission data obtained by these two approaches demonstrates a good agreement for total values, but a significant difference for spatial distribution of the data. To ensure completeness of the data, to improve their spatial resolution and also to analyse the impact of the traffic emissions, a combination of the two approaches was applied to generate the emission data used by a photochemical numerical system to simulate the atmospheric circulation and the air pollution pattern in Lisbon under summer meteorological conditions, having different emission scenarios. It was possible to conclude that an air pollution abatement strategy is urgently needed and it should take into account the strong contribution of road traffic emissions to the Lisbon air pollution levels.
- Importance of handling organic atmospheric pollutants for assessing air qualityPublication . Borrego, C.; Gomes, P.; Barros, Nelson; Miranda, A.I.Volatile organic compounds (VOCs) are the main precursors of tropospheric ozone production, playing an important role in photochemical pollution of the atmosphere and, consequently, in the degradation of air quality. Air quality photochemical models require a specific VOC profile for each different main source, based on the most important group compounds. Chromatographic techniques have been used to identify and measure VOC in Portugal. These measured values were used to simulate photochemical pollution, and modelling results were compared with those from another simulation using VOC class distributions from the literature. Ozone concentration values estimated via both simulations indicate the importance of using VOC data from Portugal instead of those obtained in different conditions.
- Influence of traffic emissions estimation variability on urban air quality modellingPublication . Borrego, Carlos; Tchepel, Oxana; Monteiro, Alexandra; Barros, Nelson; Miranda, Ana IsabelThe main objective of this work is to analyse how uncertainties in emission data of nitrogen oxides (NOx) and volatile organic compounds (VOC), originated from road traffic, influence the model prediction of ozone (O3) concentration fields. Different methods to estimate emissions were applied and results were compared in order to obtain their variability. Based on these data, different emission scenarios were compiled for each pollutant considering the minimum and the maximum values of the estimated emission range. These scenarios were used as input to the MARIV mesoscale modelling system. Simulations have been performed for a summer day in the Northern Region of Portugal. The different approaches to estimate NOx and VOC traffic emissions show a significant variability of absolute values and of their spatial distribution. Comparison of modelling results obtained from the two scenarios presents a dissimilarity of 37% for ozone concentration fields as a response of the system to a variation in the input emission data of 63% for NOx and 59% for VOC. Far beyond all difficulties and approximations, the developed methodology to build up an emission data base shows to be consistent and an useful tool in order to turn applicable an air quality model. Nevertheless, the sensitivity of the model to input data should be considered when it is used as a decision support tool.
- Urban photochemical pollution in the Iberian Peninsula: Lisbon and Barcelona airshedsPublication . Barros, Nelson; Borrego, Carlos; Toll, Isabel; Soriano, Cecilia; Jiménez, Pedro; Baldasano, José MariaNumerical simulations with photochemical transport models were independently performed for two domains situated in the Iberian Peninsula covering the Lisbon and Barcelona airsheds. Although the days chosen for simulation of the two cities are not the same, the synoptic situations in both cases, known as typical summertime situations, were similar, which allowed the development of typical mesoscale circulations, such as sea breezes and mountain and valley winds dominated by the Azores anticyclone. Emission inventories for the two areas were developed. The O3 concentrations recorded in both cities have a similar level. Nevertheless, Ox values in Barcelona are higher than in Lisbon, which may, at a first glance, indicate an apparently more oxidant atmosphere in Barcelona. Photochemical modeling for the two cities has shown that the behavior of the circulatory patterns in both urban areas is rather different, which mainly has to do with the different strengths of the sea breeze and the topography, inducing an important offshore vertical layered dimension of pollutant transport in Barcelona versus an important inland horizontal transport in Lisbon.
- Spatio-temporal prediction of atmospheric benzene (Part I)Publication . Fontes, Tânia; Barros, NelsonBenzene is a carcinogenic and genotoxic pollutant which mainly affects the people health through the inhalation. Nevertheless, this pollutant is not frequently measured by air-quality networks. To solve this problem, some models have been published to estimate benzene concentrations in the atmosphere. However, the lack of measures makes difficult the application of complex models in order to get a detailed spatiotemporal analysis, namely in urban areas. In this work was developed a simple semi-empirical model to predict benzene concentrations based on the ratio of benzene and carbon monoxide concentrations in order to predict the concentrations of this pollutant in large areas and periods with lack of benzene measurements but with higher impact in the human health. The model was applied to an urban area, the Metropolitan Area of Oporto, for a period of 12 years (1995–2006). Monthly correlations between benzene and carbon monoxide concentrations at Custóias airquality station are significant (p = 0.01) and higher in winter (rs > 0.7) than in summer (0.3 >rs >0.7). Estimate of the monthly ratio of the concentration of these two pollutants range between 199 and 305. The methodology validation shows good results (rs = 0.81) which allow, assuming the availability of carbon monoxide data, the use of this tool for areas with low benzene recorded data. The application of this methodology in the study area shows an annual average trend decrease of benzene concentrations during the study period, which may be linked to a general trend decrease of benzene emissions in European urban areas, including the study domain.
- How wide should be the adjacent area to an urban motorway to prevent potential health impacts from traffic emissions?Publication . Barros, Nelson; Fontes, Tânia; Silva, M.P.; Manso, M. ConceiçãoIn recent years, several studies show that people who live, work or attend school near the main roadways have an increased incidence and severity of health problems that may be related with traffic emissions of air pollutants. The concentrations of near-road atmospheric pollutants vary depending on traffic patterns, environmental conditions, topography and the presence of roadside structures. In this study, the vertical and horizontal variation of nitrogen dioxide (NO2) and benzene (C6H6) concentration along a major city ring motorway were analysed. The main goal of this study is to try to establish a distance from this urban motorway considered ‘‘safe’’ concerning the air pollutants human heath limit values and to study the influence of the different forcing factors of the near road air pollutants transport and dispersion. Statistic significant differences (p = 0.001, Kruskal–Wallis test) were observed between sub-domains for NO2 representing different conditions of traffic emission and pollutants dispersion, but not for C6H6 (p = 0.335). Results also suggest significant lower concentrations recorded at 100 m away from roadway than at the roadside for all campaigns (p < 0.016 (NO2) and p < 0.036 (C6H6), Mann–Whitney test). In order to have a ‘‘safe’’ life in homes located near motorways, the outdoor concentrations of NO2 must not exceed 44–60.0 lg m3 and C6H6 must not exceed 1.4– 3.3 lg m3 . However, at 100 m away from roadway, 81.8% of NO2 receptors exceed the annual limit value of human health protection (40 lg m3 ) and at the roadside this value goes up to 95.5%. These findings suggest that the safe distance to an urban motorway roadside should be more at least 100 m. This distance should be further studied before being used as a reference to develop articulated urban mobility and planning policies.
- Sharing Video Emotional Information in the WebPublication . Oliveira, Eva; Chambel, Teresa; Ribeiro, Nuno MagalhãesVideo growth over the Internet changed the way users search, browse and view video content. Watching movies over the Internet is increasing and becoming a pastime. The possibility of streaming Internet content to TV, advances in video compression techniques and video streaming have turned this recent modality of watching movies easy and doable. Web portals as a worldwide mean of multimedia data access need to have their contents properly classified in order to meet users’ needs and expectations. The authors propose a set of semantic descriptors based on both user physiological signals, captured while watching videos, and on video low-level features extraction. These XML based descriptors contribute to the creation of automatic affective meta-information that will not only enhance a web-based video recommendation system based in emotional information, but also enhance search and retrieval of videos affective content from both users’ personal classifications and content classifications in the context of a web portal.
- 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.
- Analysis of the effectiveness of the NEC Directive on the tropospheric ozone levels in PortugalPublication . Barros, Nelson; Fontes, Tânia; Silva, M.P.; Manso, M. Conceição; Carvalho, A.C.The National Emission Ceilings Directive 2001/81/CE (NEC Directive) was adopted in the European Community in 2001 and went through a revision process in 2005. One of its main objectives is to improve the protection of the environment and human health against the risks of adverse effects from ground-level ozone, moving towards the long-term objective of not exceeding critical levels proved to effectively protect the populations and ecosystems. Considering such objectives, national emission ceilings were established imposing the years 2010 and 2020 as benchmarks. Ten years later, what was the effectiveness of this Directive concerning the control of tropospheric ozone levels in Portugal? In order to answer the previous question, annual ozone precursors' emissions (NOx, NMVOC) and annual atmospheric concentrations (NOx and O3) were analyzed between 1990 and 2011. The background concentrations were assessed in each environment type of air quality station (urban, suburban and rural) through their annual mean ozone concentration and the hourly information threshold exceedances (episodic peak levels). To evaluate the statistical differences in the inter-annual episodic peak levels, a Peak Ozone Index (POIx) was defined and calculated. The results show that, despite the achievement on the emissions NEC Directive goals, associated to the reduction of ozone precursors' emissions, and the decrease of ozone episodic peak levels, the mean tropospheric ozone concentrations significantly increased between 2003 and 2007 (p < 0.05) although the number of exceedances to the information threshold (180 mg m3 ) has decreased. During the period of 1990e2000, before the implementation of the NEC Directive, the mean ozone values were 25% lower in rural stations, 26% in urban stations and 12% in suburban stations, demonstrating that the NEC policy based on NOx and NMVOCs emissions reduction does not lead to an effective overall reduction of ozone concentrations considering the reduction on these pollutants independently. Indeed, the mesoscale ozone production and/or the long range advection may play also an important role as the analysis of Mace Head ozone concentrations suggests. Above all, and due to its non-linear interactions in the ozone chemical balance, the NEC directive should impose emissions' reduction respecting the NOx/NMVOC ratio instead of consider it as a mere guideline value. The mesoscale photochemical ozone production should be carefully analyzed under the new policies, namely in coastal countries like Portugal where the mesoscale circulations play a crucial role in this type of phenomena.