Richard Tavares

CFD modelling of the aerodynamic effect of trees on urban air pollution dispersion

The current work evaluates the impact of urban trees over the dispersion of carbon monoxide (CO) emitted by road traffic, due to the induced modification of the wind flow characteristics. With this purpose, the standard flow equations with a kε closure for turbulence were extended with the capability to account for the aerodynamic effect of trees over the wind field. Two CFD models were used for testing this numerical approach. Air quality simulations were conducted for two periods of 31h in selected areas of Lisbon and Aveiro, in Portugal, for distinct relative wind directions: approximately 45° and nearly parallel to the main avenue, respectively. The statistical evaluation of modelling performance and uncertainty revealed a significant improvement of results with trees, as shown by the reduction of the NMSE from 0.14 to 0.10 in Lisbon, and from 0.14 to 0.04 in Aveiro, which is independent from the CFD model applied. The consideration of the plant canopy allowed to fulfil the data quality objectives for ambient air quality modelling established by the Directive 2008/50/EC, with an important decrease of the maximum deviation between site measurements and CFD results. In the non-aligned wind situation an average 12% increase of the CO concentrations in the domain was observed as a response to the aerodynamic action of trees over the vertical exchange rates of polluted air with the above roof-level atmosphere; while for the aligned configuration an average 16% decrease was registered due to the enhanced ventilation of the street canyon. These results show that urban air quality can be optimised based on knowledge-based planning of green spaces.

Emission modelling of hazardous air pollutants from road transport at urban scale

Abstract This study is focused on the development of a modelling approach to quantify emissions of traffic-related hazardous air pollutants in urban areas considering complex road network and detailed data on transport activity. In this work a new version of the Transport Emission Model for line sources has been developed for hazardous pollutants (TREM-HAP). Emission factors for benzene, 1,3-butadiene, formaldehyde, acetaldehyde, acrolein, naphthalene and also particulate matter (PM2.5) were implemented and the model was extended to integrate a probabilistic approach for the uncertainty quantification using Monte-Carlo technique. The methodology has been applied to estimate road traffic emissions in Porto Urban Area, Portugal. Hourly traffic counts provided by an automatic counting system were used to characterise the spatial and temporal variability of the number of vehicles, vehicle categories and average speed at different road segments. The data for two summer and two winter months were processed to o...

Impact of urban planning alternatives on air quality: URBAIR model application

In the last decades, the study of the urban structure impacts on the quality of life and on the environment became a key issue for urban sustainability. Nowadays the relevance of urban planning for the improvement of the interactions between different land uses and economic activities, and also towards a more sustainable urban metabolism, is consensually accepted. A major interest relies on understanding the role of planning on induced mobility patterns and thereafter on air quality, particularly related with the increasing use of private cars. This is one of the main objectives of BRIDGE, a research project funding by the European Commission under the 7 th Framework Programme and focused on “SustainaBle uRban plannIng Decision support accountinG for urban mEtabolism”. In this scope, and to evaluate the impact on air quality due to different city planning alternatives (PA), the urban scale air quality modelling system URBAIR was applied to selected areas in Helsinki (Finland), Athens (Greece) and Gliwice (Poland), to estimate traffic related emissions and induced pollutant concentration of different air pollutants, in a hourly basis for the entire year of 2008. For the Helsinki study case the results suggest that urban traffic and building placement considered on the different PA have an influence on local air quality despite no significant concentration levels. In the Athens case study some PA induce a decrease on traffic flows with an improvement of the air quality over the domain. On the contrary, other leads to an increase of PM10 in selected hotspots. The simulations for the Gliwice study case show minor changes between the baseline and the PA, since the proposed interventions do not imply major changes in traffic flows.

Air quality modelling as a tool for sustainable urban traffic management

This work intends to assess the impact of road traffic management on urban air quality at the street level. At the core of the applied methodology is the numerical modelling of wind flow and air pollutants dispersion in a typical European urban environment. Through the application of a Computational Fluid Dynamics (CFD) model, the synergies between the 3D configuration of the street-canyon, in addition to the impacts on the dispersion of CO and PM10 emitted by vehicles, were evaluated. Air quality simulations were performed for a study domain of approximately 2501000 m 2 in the downtown of a medium sized Portuguese town, with average daily traffic of 21,400 vehicles. Different traffic scenarios were analysed based on the modification of the number and location of traffic lanes for typical meteorological boundary conditions. Complex dispersion patterns were obtained due to the effect of buildings and trees on the wind flow. Moreover, simulations for the different scenarios have shown distinct behaviours of the air pollutants due to the prevailing wind direction and road positioning. It was concluded that, for typical conditions, the closure of the two traffic lanes located on the south side of the main avenue and the two adjacent streets is the best solution for air quality improvement. This scenario leads to a 31% reduction in CO and PM10 concentrations on the North sidewalk and 81% on the South sidewalk when comparing to present conditions. The other alternative leads to a reduction of, respectively, 70% and 20%. The first scenario also leads to maximum decreases of 57% and 59%, respectively, in the CO and PM10 peak concentrations. These conclusions stress the importance of integrating the knowledge provided by the application of CFD models in urban planning and road traffic management with the goal of promoting urban sustainability.

Individual Exposure to Air Pollutants in a Portuguese Urban Industrialized Area

Industrial development from the second half of the 20th century coupled with population growth and concentration in urban areas has accentuated the concern for potential effects and impacts from air pollutant emissions on environmental and human health. This study examined the Estarreja region, an urban area that has one of the largest chemical complexes in Portugal, a complex that was recently under expansion. In the scope of the INSPIRAR project, individual daily exposure of a group of individuals to particulate matter of 10 μm aerodynamic diameter (PM10) and nitrogen dioxide (NO2) in two phases was determined using a microenvironmental approach. In this context, personal daily activity profiles of individuals were established for their normal routine by personal interviews. These profiles enabled determination of where each individual was at each moment of the day. Utilizing this information with hourly air quality maps simulated with URBAIR air quality model and indoor/outdoor relationships, it was possible to calculate personal daily exposure of each individual to air pollutants. Results from the analysis of daily activity profiles showed a high level of sedentariness of this population and long durations spent indoors. The studied individuals displayed high personal PM10 and NO2 exposure variability. Data demonstrated possible error when a single concentration measurement was assumed as a proxy of exposure. In general, no significant differences were found between the two population groups, indicating that workers of the chemical complex were not exposed to a greater extent to PM10 and NO2 than the general population working in the same area.

Monitoring fire-fighters' smoke exposure and related health effects during Gestosa experimental fires

The main objective of this study is to contribute to the scientific knowledge regarding fire-fighters’ exposure to smoke and its related health effects. Forest fire experiments were developed with an extensive number of measurements of individual exposure to smoke pollutants and of medical parameters for a group of fire-fighters. For the smoke exposure monitoring, ten fire-fighters from four different fire brigades were selected. The fire-fighters’ individual exposure to toxic gases and particulate matter was monitored with portable devices, and their location in time was registered with GPS equipment. For all the monitored fire-fighters, air pollutant concentration values acquired during the fire experiments were beyond the limits recommended by the World Health Organization (WHO), namely for PM2.5, CO and NO2. Daily averages of PM2.5 concentration values as high as 738 µg.m -3 were obtained, well above the recommended limit of 25 µg.m -3 . In terms of CO, hourly averaged values higher than 73,000 µg.m -3 were monitored, clearly above the 30,000 µg.m -3

Effects Of Road Traffic Scenarios On HumanExposure To Air Pollution

Human exposure to air pollution has been identified as a major problem due to its known impact on human health. Particulate matter is a pollutant which rises special concern due to the adverse health effects on sensitive groups of the population, such as asthmatic children. This study is part of the SaudAr research project which main objective was to assess the air quality effects on the health of a population group risk (asthmatic school children) living in an urban area (Viseu). The aim of this paper is to investigate the influence of road traffic emissions on air quality and consequently, on human exposure. For this purpose, the CFD model VADIS integrating an exposure module has been applied over the town of Viseu, for the periods of one week in winter and one week in summer, to four different situations: the reference year (2006) and three future scenarios for the year 2030, BAU, Green and Grey scenario. The differences among the scenarios include changes on the existing land use, the vehicle fleet composition, the mobility, the vehicle technologies and the fuel types. Field campaigns were performed in order to obtain information about vehicle fleet in the town of Viseu and mobility patterns. The quantification of road traffic emissions and the hourly traffic emissions patterns for all scenarios was carried out by the application of the TREM model. The results reveal an increase in PM10 emissions, concentrations and exposure in all future scenarios, particularly in winter with an increase around 80% in the BAU and Grey scenarios and only 34% in the Green scenario.

Numerical modelling of the impact of wildland-urban interface fires on Coimbra air quality.

Forest fires are a major emission source of pollutants to the atmosphere with several adverse impacts on human health and ecosystems either at local, regional or global scales. Entire populations can be exposed to hazardous concentrations of toxins, especially when fire occurs in the vicinity of cities, as recently drawn by large wildfires in Southeast Asia, Australia, South America or Russia, but also Southern Europe, namely in Portugal. Nowadays there is a growing concern about the increase in both the frequency and the severity of forest fires spreading in the urban wildland interface (WUI) as a consequence of the escalation of urban development among or adjacent to wildlands. The main purpose of this paper is to estimate the impact of wildland forest fires on the air quality of a city in Portugal. Aiming to take into account the effect of a larger atmospheric scale in the very local urban one, a multi-scale approach was adopted, which implied the link between a chemistry-transport mesoscale model (LOTOS-EUROS) and a microscale computational fluid dynamics (CFD) model. Forest fire emissions were estimated based on specific southern European emission factors, type of vegetation, area burned and fire behaviour, and were incorporated in the emission input data of the numerical modelling system. Results confirm the strong impact of forest fires on the urban air pollution levels. Statistical indicators were used to validate the modelling application through the comparison of results to measured air quality data. This modelling approach has got very good performance skills showing the possibility of applying this kind of system to analyse the relation between forest fires and urban air pollution.