Joana Valente

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.

Airways changes related to air pollution exposure in wheezing children

In this study, we aimed to evaluate the relationship between individual total exposure to air pollution and airway changes in a group of 51 wheezing children. Respiratory status was assessed four times (January 2006, June 2006, January 2007 and June 2007) during a 1-week period through a standardised questionnaire, spirometry, exhaled nitric oxide fraction and pH in exhaled breath condensate (EBC). Concentrations of particles with a 50% cut-off aerodynamic diameter of 10 µm (PM10), O3, NO2 and volatile organic compounds were estimated through direct measurements with an ad hoc device or air pollution modelling in the childrens schools and at their homes in the same 4 weeks of the study. For each child, total exposure to the different air pollutants was estimated as a function of pollutant concentrations and daily activity patterns. Increasing total exposure to PM10, NO2, benzene, toluene and ethylbenzene was significantly associated with a decrease of forced expiratory volume in 1 s (FEV1) and with an increase of change in FEV1. Increasing exposure to NO2 and benzene was also related to a significant decrease of FEV1/forced vital capacity. Increasing exposure to PM10, NO2, benzene and ethylbenzene was associated with acidity of EBC. This study suggests an association in wheezing children between airway changes and total exposure to air pollutants, as estimated by taking into account the concentration in the various microenvironments attended by the children.

Smoke measurements during Gestosa-2002 experimental field fires

Currently, there is a growing awareness that smoke produced during forest fires can expose individuals and populations to hazardous concentrations of air pollutants. Aiming to contribute to a better understanding of the air pollution phenomenon associated with forest fires, this paper presents and analyses the atmospheric emissions and air quality concentration measurements performed in the 2002 fire experiments at Gestosa, Central Portugal. Two vehicles were equipped with a meteorological station and air quality analysers that were turned on continuously to acquire concentrations of particulate matter, nitrogen oxides and carbon monoxide. Nitrogen and sulfur dioxides were measured using a grid of fixed passive samplers. Also, firefighters and research-team members used passive samplers during the experiments in order to estimate the human exposure to these pollutants. Measurements of volatile organic compound emissions, using Tedlar bags, were carried out. Results were analysed taking into account not only the concentration values but also the variables involved, such as the combustion phase and the meteorology, and identifying possible relationships between them. Despite the small size of the burning plots when compared to wildfires, the measured levels of pollutants were however considerable, indicating the effect of these experiments on the local air quality and stressing the serious levels of air pollution that can be expected during wildfires.

Wildland Smoke Exposure Values and Exhaled Breath Indicators in Firefighters

Smoke from forest fires contains significant amounts of gaseous and particulate pollutants. Firefighters exposed to wildland fire smoke can suffer from several acute and chronic adverse health effects. Consequently, exposure data are of vital importance for the establishment of cause/effect relationships between exposure to smoke and firefighter health effects. The aims of this study were to (1) characterize the relationship between wildland smoke exposure and medical parameters and (2) identify health effects pertinent to wildland forest fire smoke exposure. In this study, firefighter exposure levels of carbon monoxide (CO), nitrogen dioxide (NO2), and volatile organic compounds (VOC) were measured in wildfires during three fire seasons in Portugal. Personal monitoring devices were used to measure exposure. Firefighters were also tested for exhaled nitric oxide (eNO) and CO before and after their firefighting activities. Data indicated that exposure levels during firefighting activities were beyond limits recommended by the Occupational Exposure Standard (OES) values. Medical tests conducted on the firefighters also indicated a considerable effect on measured medical parameters, with a significant increase in CO and decrease in NO in exhaled air of majority of the firefighters.

Local-scale modelling system to simulate smoke dispersion

The main purpose of this paper is to present a fire behaviour system, developed to estimate fire progression, smoke dispersion and visibility impairment, at a local scale, and to evaluate its performance by comparing results with measurements from the Gestosa 2004 experimental field fires. The system is an improvement of two already available numerical tools, DISPERFIRE (Miranda et al. 1994) and FireStation (Lopes et al. 2002), which were integrated. FireStation is a software system aimed at the simulation of fire spread over complex topography. DISPERFIRE is a real-time system developed to simulate the dispersion in the atmosphere of the pollutants emitted during a forest fire. In addition, a model for the estimation of visibility impairment, based on the relationship between air pollutants concentration and visibility, was included in DISPERFIRE. The whole system was developed using a graphical interface, previously created for FireStation, which provides user-friendliness and easily readable output to facilitate its application under operational conditions. The system was applied to an experimental field fire and the main results were compared with experimental air pollutant concentration measured values. The performance of the model in predicting pollutant concentrations was good, particularly for NO2 and PM10.

Pedestrian Exposure to Air Pollution in Cities: Modeling the Effect of Roadside Trees

The exposure of students to traffic-emitted carbon monoxide (CO) in their daily walk to school is evaluated, with a particular emphasis on the effect of trees and route choice. The study is focused on the city centre of Aveiro, in central Portugal. Time evolution of the georeferenced location of an individual is tracked with a GPS for different alternative walking routes to a school. Spatial distribution of CO concentration is simulated with a computational fluid dynamics (CFD) model. An exposure model is developed that associates the georeferenced location of the student with the computed air quality levels (at an average breathing height) for that specific grid cell. For each individual, the model calculates the instantaneous exposure at each time frame and the mean value for a given period. Results show a general benefit induced by the trees over the mean exposure of the student in each route. However, in the case of instantaneous exposure values, this is not consistent along the entire period. Also, the variability of the estimated exposure values indicates the potential error that can be committed when using a single value of air quality as a surrogate of air pollution exposure.

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.

Forest Fire Emissions and Air Pollution in Southern Europe

Forest fires are one of the most impressive forces of nature. Their disturbing effects include, among many others, the emission of large amounts of gases and particles to the atmosphere, with significant impacts on air quality and human health. The work here presented summarizes the current state of research in what respects to the atmospheric emissions of forest fires and their relationship with air quality. An overview of the current emission models is presented, including a collection of emission factors suitable for application to southern European forest fires. Emission measurement techniques, as well as air quality measurements, are presented under the framework of Lousa 2004 field fire experiments. The extreme fire events that took place in the summer of 2003 in southern Europe are illustrated with two case studies for Portugal. Two air quality modelling systems were applied, LOTOS-EUROS and AIRFIRE, revealing the severe degradation of air quality due to forest fires, namely in what concerns particulate matter and ozone levels. The need to integrate air quality policies in forest management in order to reduce the number of air pollution episodes besides the risk of unwanted fires is a clear outcome of this chapter.

The Role Of PM10 In Air Quality And ExposureIn Urban Areas

In recent years, there has been an increase of scientific studies confirming that longand short-term exposure to particulate matter pollution leads to adverse health effects. The calculation of human exposure in urban areas is the main objective of the current work combining information on pollutant concentration in different microenvironments and personal time-activity patterns. Two examples of PM10 exposure quantification using population and individual approaches are presented. The results are showing important differences between outdoor and indoor concentrations and stressing the need to include indoor concentrations quantification in the exposure assessment.

Children’s exposure to traffic-related pollution: assessment of CO exposure in a typical school day

This paper evaluates the exposure of four children to carbon monoxide (CO) in two different classrooms during the time spent in school in a typical school day, using a numerical modelling approach. The study is focused on an area of 550 × 550 m 2 centred at a primary school of the city of Aveiro, in central Portugal, which is located close to a road with moderate traffic and has naturally ventilated rooms. Air quality data were measured in the school yard. Traffic emissions were estimated with TREM model, using traffic counts data. Simulations of CO concentrations in the study domain were performed with the computational fluid dynamics model VADIS, considering the influence of buildings and trees over the dispersion. Indoor concentrations were simulated using a mass transfer approach. Results show that the individual exposure of children is spatially dependent, as a consequence of the wind flow and air pollutant dispersion patterns.