This paper is devoted to the development and evaluation of a fast three-dimensional Eulerian model for dispersion inside and above the urban canopy layer. Spatially averaged wind and diffusivity coefficient profiles obtained from the commercial Computational Fluid Dynamics (CFD) code FLUENT are used as input in the developed model. This model is numerically solved by means of a finite volume method and mean concentration outputs are compared with the corresponding results from FLUENT. We considered several canopies made of arrays of cubes laid in staggered position. Results from the comparison suggest the potential of this type of simple modelling approach. As the spatially averaged wind and diffusivity profiles are strongly dependent from the mean morphometry properties of the urban canopy, these results, though preliminary, highlight the necessity of using specific turbulence closure models where building effects at the neighbourhood scale are taken into account.

This paper presents a novel methodology for representing neighbourhood-scale flow within and above urban canopies based on detailed urban morphometry analyses and numerical flow simulations. The first step of the methodology consists in the representation of the urban areas in terms of “synthetic” neighbourhoods based on geometric parameters only. The second step consists in assessing the fluid dynamics relevance of such representation by comparing flow results for full scale city morphometry with those using a synthetic representation. Herein numerical simulations are used as benchmark data for assessing the aerodynamics relevance of given geometric parameters. Finally, a new parameterisation for the internal boundary layer growth over cities is discussed in which the urban area is represented by a cluster of synthetic neighbourhoods. Our findings are relevant for the development of more realistic urban flow modelling approaches suitable for implementation of urban effects into mesoscale models.

This paper discusses the combined influence of building morphology and trees on air pollutant concentrations in the Marylebone neighbourhood (central London). Computational Fluid Dynamics (CFD) simulations are performed with OpenFOAM using the k-ε model. Aerodynamic and deposition effects of Platanus acerifolia trees are considered. While aerodynamic effects are treated as typically done in the literature, i.e. as a porous media, for the deposition an enhanced model with an additional sink term was implemented. CFD results are compared with UK AURN (Automatic Urban and Rural Network) station concentrations. Several meteorological conditions are analysed based on London City Airport weather station data, with attention to prevailing winds. CFD simulations show that trees trap air pollution by up to about 7% at the Marylebone monitoring station in the spring, autumn and summer seasons, suggesting that the aerodynamic effects are similar over the different leaf seasons. Aerodynamic effects are more important at lower wind speeds causing little turbulent dispersion. Deposition effects are found to be 4 times less important with reductions of up to about 2%, with more deposition in summer due to a greater leaf area density. Furthermore, for winds parallel to Marylebone Road, the aerodynamic effects decrease concentrations suggesting that in such cases trees could be considered as a mitigation measures. This is different from perpendicular winds for which trees exacerbate trapping, as found in previous studies. The analysis of concentration levels obtained from CFD simulations across the whole street confirms a beneficial aerodynamic dispersive effect of trees of 0.7% in summer time for all wind directions averaged at a wind speed of 5 m/s (yearly average wind speed observed in the area). Results highlight the need to account for both aerodynamic and dispersion effects of trees in CFD modelling to achieve a comprehensive evaluation and help city planners with a sustainable design of trees in urban environments.

This paper is devoted to the study of flow and pollutant dispersion within different urban configurations by means of wind tunnel experiments and Computational Fluid Dynamics (CFD) simulations. The influence of the building packing density was evaluated in terms of ventilation efficiency. We found that air entering the array through the lateral sides and that leaving through the street roofs increased and the lateral spread of the pollutant released from a ground level line source decreased with increasing packing density. Ventilation efficiency concepts developed for indoor environments appear a promising tool for evaluating the urban air quality as well.

This paper first discusses the aerodynamic effects of trees on local scale flow and pollutant concentration in idealized street canyon configurations by means of laboratory experiments and Computational Fluid Dynamics (CFD). These analyses are then used as a reference modelling study for the extension a the neighbourhood scale by investigating a real urban junction of a medium size city in southern Italy.A comparison with previous investigations shows that street-level concentrations crucially depend on the wind direction and street canyon aspect ratio W/H (with W and H the width and the height of buildings, respectively) rather than on tree crown porosity and stand density. It is usually assumed in the literature that larger concentrations are associated with perpendicular approaching wind. In this study, we demonstrate that while for tree-free street canyons under inclined wind directions the larger the aspect ratio the lower the street-level concentration, in presence of trees the expected reduction of street-level concentration with aspect ratio is less pronounced.Observations made for the idealized street canyons are re-interpreted in real case scenario focusing on the neighbourhood scale in proximity of a complex urban junction formed by street canyons of similar aspect ratios as those investigated in the laboratory. The aim is to show the combined influence of building morphology and vegetation on flow and dispersion and to assess the effect of vegetation on local concentration levels. To this aim, CFD simulations for two typical winter/spring days show that trees contribute to alter the local flow and act to trap pollutants. This preliminary study indicates that failing to account for the presence of vegetation, as typically practiced in most operational dispersion models, would result in non-negligible errors in the predictions.

Background: Air pollution is a major global environmental risk factor. Since people spend most of their time indoors, the sole measure of outdoor concentrations is not sufficient to assess total exposure to air pollution. Therefore, the arising interest by the international community to indoor-outdoor relationships has led to the development of various techniques for the study of emission and exchange parameters among ambient and non-ambient pollutants. However, a standardised method is still lacking due to the complex release and dispersion of pollutants and the site conditions among studies. Methods: This review attempts to fill this gap to some extent by focusing on the analysis of the variety of site-specific approaches for the assessment of particulate matter in work and life environments. Results: First, the main analogies and differences between indoor and outdoor particles emerging from several studies are briefly described. Commonly-used indicators, sampling methods, and other approaches are compared. Second, recommendations for further studies based on recent results in order to improve the assessment and management of those issues are provided. Conclusions: This review is a step towards a comprehensive understanding of indoor and outdoor exposures which may stimulate the development of innovative tools for further epidemiological and multidisciplinary research.

This paper is devoted to the study of pollutant concentration distribution within urban-like geometries. By applying efficiency concepts originally developed for indoor environments, the term ventilation is used as a measure of city " breathability" It can be applied to analyse pollutant removal within a city in operational contexts. This implies the evaluation of the bulk flow balance over the city and of the mean age of air. The influence of building packing density on flow and pollutant removal is, therefore, evaluated using those quantities. Idealized cities of regular cubical buildings were created with packing density ranging from 6.25% to 69% to represent configurations from urban sprawl to compact cities. The relative simplicity of these arrangements allowed us to apply the Computational Fluid Dynamics (CFD) flow and dispersion simulations using the standard k- e{open} turbulence model. Results show that city breathability within the urban canopy layer is strongly dependent from the building packing density. At the lower packing densities, the city responds to the wind as an agglomeration of obstacles, at larger densities (from about 44%) the city itself responds as a single obstacle. With the exception of the lowest packing density, airflow enters the array through lateral sides and leaves throughout the street top and flow out downstream. The air entering through lateral sides increases with increasing packing density.At the street top of the windward side of compact building configurations, a large upward flow is observed. This vertical transport reduces over short distance to turn into a downward flow further downstream of the building array. These findings suggest a practical way of identifying city breathability. Even though the application of these results to real scenarios require further analyses the paper illustrates a practical framework to be adopted in the assessment of the optimum neighbourhood building layout to minimize pollution levels.

This paper investigates pollutant removal at pedestrian level in urban canopy layer (UCL) models of medium packing density (λp = λf = 0.25) using computational fluid dynamics (CFD) simulations. Urban size, building height variations, wind direction and uniform wall heating are investigated. The standard and RNG k-ε turbulence models, validated against wind tunnel data, are used. The contribution of mean flows and turbulent diffusion in removing pollutants at pedestrian level is quantified by three indicators: the net escape velocity (NEV), the pollutant transport rate (PTR) across UCL boundaries and their contribution ratios (CR).Results show that under parallel approaching wind, after a wind-adjustment region, a fully-developed region develops. Longer urban models attain smaller NEV due to pollutant accumulation. Specifically, for street-scale models (~100 m), most pollutants are removed out across leeward street openings and the dilution by horizontal mean flows contributes mostly to NEV. For neighbourhood-scale models (~1 km), both horizontal mean flows and turbulent diffusion contribute more to NEV than vertical mean flows which instead produce significant pollutant re-entry across street roofs. In contrast to uniform height, building height variations increase the contribution of vertical mean flows, but only slightly influence NEV. Finally, flow conditions with parallel wind and uniform wall heating attain larger NEV than oblique wind and isothermal condition.The paper proves that by analysing the values of the three indicators it is possible to form maps of urban breathability according to prevailing wind conditions and known urban morphology that can be of easy use for planning purposes.

The present paper is devoted to the evaluation of the contribution of shipping emissions to local concentrations in a relatively large port city (Brindisi) located in southern Italy and characterized by a traffic volume of over 2,000 ships/year. A procedure for building an emission inventory at fine scale is reported along with the modelling study to estimate concentrations in the area. Results for two base years (2010, 2011) show that shipping emissions and associated concentrations were strictly dependent on seasonality and larger contributions were found for NOX. This confirms, at least for Italian ports, that NOX are major pollutants from shipping sources which need to be carefully accounted for in the assessment of air quality in coastal/port cities.

The aim of this paper is to describe the use of a general methodology tailored to the evaluation of micro-scale meteorological models applied to flow and dispersion simulations in urban areas. This methodology, developed within COST 732, has been tested through a large modelling exercise involving many groups across Europe. The major test case used is the Mock Urban Setting Test (MUST) experiment representing an idealised urban area. It is emphasised that a full model evaluation is problem-dependent and requires several activities including a statistical validation based on a careful choice of the metrics for the comparison with measurements.

Wind tunnel measurements of the total drag force for aligned arrays of cubes exposed to two different boundary-layer flows at three flow velocities are discussed. The drag force for eight different building packing densities λp (from 0.028 to 1) is measured with a standard load cell generating a novel dataset. Different λp are reproduced by increasing the number of buildings on the same lot area; this represents a real situation that an urban planner is faced with when a lot area of a given (fixed) size is allocated to the development of new built areas. It is assumed that the surrounding terrain is uniform and there is a transition from a given roughness (smooth) to a new roughness (rough). The approaching flow will adjust itself over the new surface within a distance that in general may be larger than the horizontal length covered by the array. We investigate the region where the flow adjustment occurs. The wide range of packing densities allowed us to analyse in detail the evolution of the drag force. The drag force increases with increasing packing densities until it reaches a maximum at an intermediate packing density (λp = 0.25 in our case) followed by a slight decrease at larger packing densities. The value of the drag force depends on the flow adjustment along the array which is evaluated by introducing the parameter “drag area” to retrieve information about the drag distribution at different λp. Results clearly suggest a change of the distribution of the drag force, which is found to be relatively uniform at low packing densities, while most of the force acts on first rows of the arrays at large packing densities. The drag area constitutes the basis for the formulation of a new adjustment length scale defined as the ratio between the volume of the air within the array and the drag area. The proposed adjustment length scale automatically takes into account the change in drag distribution along the array for a better parameterization of urban effects in dispersion models.

This study investigates flow and turbulence within two arrays of staggered high-rise buildings. Each array is characterized by a packing density (λp) of 0.25 and a uniform building width B and height H, with H=2B in one array and H=2.67B in the other. Wind tunnel measurements and numerical simulations are performed to evaluate the wind reduction within the arrays, and explore the main mechanisms of rural wind flowing through such idealised arrays and how rural air distributes within them. Results show a quick wind reduction through the arrays. Wind strongly interacts with buildings producing downward motion near the leeward top corner of each building and upward motion near the windward top corner. These vertical flows across the street roof level mostly contribute to the air exchange and ventilation in such staggered arrays. The analysis also shows that increasing the building height does not have critical influence on flow and turbulence at pedestrian level.

The present paper is aimed at the analysis of flow and pollutant dispersion in a portion of the Canal Grande (Grand Canal) in Venice (Italy) by means of both Computational Fluid Dynamics (CFD) FLUENT simulations and wind tunnel experiments performed at the University of Gävle (Sweden). For this application, Canal Grande can be viewed as a sort of street canyon where the bottom surface is water and bus boat emissions are the major source of pollution. Numerical investigations were made to assess the effect of the water surface on air flow and pollutant concentrations in the atmosphere. One of the challenges has been to deal with the interface between two immiscible fluids which requires ad-hoc treatment of the wall in terms of the numerical scheme adopted and the grid definition which needs to be much finer than in typical numerical airflow simulations in urban street canyons. Preliminary results have shown that the presence of water at the bottom of the street canyon modifies airflow and turbulence structure with direct consequences on concentration distribution within the domain.

The decision on the fitness for purpose of a simulation should be based on the quantity of interest. However, in general, models are used because there is no complete experimental information available on the quantity of interest, so a direct judgement is not possible. The aim of this article is to put in light this dichotomy, and propose a methodology to decide if a simulation is fit for purpose, based on the experimental data available and an ensemble of simulations. The methodology is illustrated with one example of microscale simulations.

This paper presents the impact of different scenarios of future emissions from ships taking into account the implementation of the Directive 2012/33/EU as far as the sulphur content in fuels is concerned in the port of Brindisi. This is one of the most important of the Adriatic Sea, located in the south-east coast of Italy. Ship emissions are estimated through the MEET methodology using appropriate emission factors for manoeuvring and hoteling phases. Numerical simulations of NOx, SO2 and primary PM emissions and dispersion are performed by means of the mesoscale model BOLCHEM coupled with ADMS-Urban dispersion model. This study extends our previous work presented at the 15th Harmo Conference in Madrid, by considering different sulphur content in the fuel oil to analyse the impact of future emission scenarios on the foreseen reduction of pollutant concentrations and assess the potential improvement of air quality in the port area.

We present a modelling approach to investigate the impact of ship emissions in the port of Brindisi (IT) on local air quality. The focus is on the impact on pollutant concentrations due to the implementation of the MARPOL Annex VI and the associated NOx technical code 2008 (concerning NOx emissions) and the Directives 2005/33/EU-2012/33/EU (concerning the sulphur content of maritime fuels). Emissions are estimated through an adapted MEET methodology using appropriate emission factors for manoeuvring and hotelling phases. Numerical simulations of NOx, SO2 and primary PM10 are performed by means of the mesoscale model BOLCHEM coupled off-line with ADMS-Urban. The impact of present and future ship emissions on air quality in the port area is evaluated. After the implementation of the Directives 2005/33/EU-2012/33/EU for the year 2012 SO2 showed a significant concentration reduction especially close to the port area, while primary PM10 concentration reduction was minor, as well as that of NOx, as a consequence of the NOx technical code. No significant reductions were found for the year 2020.

The impact of ship emissions on the surface concentration of nitrogen oxides (NOx) and ozone (O3) in the Mediterranean area of the harbour of Brindisi (IT) has been investigated. Numerical simulations have been performed for a summer period of the year 2012, at different spatial scale, using the meso-scale BOLCHEM and the local-scale ADMS-Urban models. Results show that while average ground concentration of primary pollutant NOx increases in the area surrounding the port, a decrease in O3 concentration is observed.

This paper presents numerical simulations of the aerodynamic effects of trees on the flow field and dispersion of trafficoriginated pollutants in an urban street canyon of W/H = 1 with a perpendicular approach flow. Large Eddy Simulation (LES) is employed for the investigation and is validated against wind tunnel (WT) experiment. Comparisons is made between an empty street canyon and one containing avenue-like tree planting of pore volume, Pvol = 96%. In the presence of trees, both measurements and simulations show considerably larger pollutant concentrations near the leeward wall and slightly lower concentrations near the windward wall in comparison to the tree-free case.

This work analyses the aerodynamic effects of avenue-like tree planting on the flow field and dispersion of pollutants in urban street canyons by means of large eddy simulations (LES) coupled with the Dynamics Smagorinsky-Lilly Subgrid scale model and the advection-diffusion module for concentration prediction using the commercial CFD software FLUENT. Flow and concentration levels are compared between an empty (i.e. tree-free) street canyon and one containing avenue-like tree planting with two porosities of λ = 80 m-1 and λ = 200 m-1. In the presence of trees, considerably larger pollutant concentrations near the leeward wall and slightly lower concentrations near the windward wall are observed in comparison to the tree-free case. The difference in porosities did not play a significant role. Simulation results obtained by LES are agreeable to wind tunnel (WT) measurements due to the resolution of the internally induced fluctuations.

This paper looks at the application of Computational Fluid Dynamics (CFD) and integral approaches to the study of effects of obstacles on pollutant dispersion from a point source placed within an idealised urban area (MUST). This study is part of a modelling exercise within the COST Action 732. Numerical results are compared with wind tunnel data. We use the CFD code FLUENT and the dispersion model ADMS-Urban. The CFD model predicts concentrations more accurately than the integral model. However, both models results satisfy accepted statistical criteria, showing that those criteria should not be the only way of evaluating a model.

Prediction accuracy of pollutant dispersion within an urban street canyon of width to height ratio W/. H=1 is examined using two steady-state Reynolds-averaged Navier-Stokes (RANS) turbulence closure models, the standard k-ε and Reynolds Stress Model (RSM), and Large Eddy Simulation (LES) coupled with the advection-diffusion method for species transport. The numerical results, which include the statistical properties of pollutant dispersion, e.g. mean concentration distributions, time-evolution and three-dimensional spreads of the pollutant, are then compared to wind-tunnel (WT) measurements. The accuracy and computational cost of both numerical approaches are evaluated. The time-evolution of the pollutant concentration (for LES only) and the mean (time-averaged) values are presented. It is observed that amongst the two RANS models, RSM performed better than standard k-ε except at the centerline of the canyon walls. However, LES, although computationally more expensive, did better than RANS in predicting the concentration distribution because it was able to capture the unsteady and intermittent fluctuations of the flow field, and hence resolve the transient mixing process within the street canyon.

This paper analyses the contribution of mean flow and turbulence to city breathability within urban canopy layers under the hypothesis that winds from rural/marine areas are sources of clean air (inhale effect) and main contributors to local-scale pollutant dilution (exhale effect). Using Computational Fluid Dynamics (CFD) simulations, several idealized long streets flanked by tall buildings are investigated for wind flow parallel to the street axis. Aspect ratios (building height/street width) ranging from 2 to 4 and street lengths ranging from neighborhood scales (~ 1 km in full scale) to city scales (~ 10 km in full scale) are analyzed. To assess the inhale effect, the age of air concept is applied to quantify the time taken by a parcel of rural/marine air to reach a reference location within the urban canopy layer. To simulate the exhale effect, removal of pollutants released from a ground level source is considered. Numerical results agree with wind tunnel observations showing that a bulk portion of rural/marine air enters the streets through windward entries, a smaller part of it leaves through street roofs and the remaining fraction blows through the street aiding pollutant dilution. Substantial differences between neighborhood-scale and city-scale configurations are found. For neighborhood-scale models, pollutant removal by rural/marine air is mainly associated to mean flow along the streets. Breathability improves in streets flanked by taller buildings since in this case more rural/marine air is captured inside canyons leading to stronger wind along the street. For city-scale models, pollutant removal due to turbulent fluctuations across street roofs competes with that due to mean flows along the street. Breathability improves in streets flanked by lower buildings in which less rural/marine air is driven out and pollutant removal by turbulent fluctuations is more effective. Based on these findings, suggestions for ventilation strategies for urban areas with tall buildings are provided.

This paper employs Computational Fluid Dynamic (CFD) simulations to investigate the influence of ground heating intensities and viaduct configurations on gaseous and particle dispersion within two-dimensional idealized street canyons (typical aspect ratio H/W = 1) and their transport from outdoor to leeward and windward rooms of naturally-ventilated buildings. Without viaduct, the ground heating exists at the street ground above which the pollutant source is located, while in the presence of viaduct the ground heating only occurs at the viaduct ground surface and pollutant source is slightly above the viaduct. Results show that viaduct significantly reduces overall spatial mean indoor concentrations of gaseous pollutant (<K>) and indoor particle number (PN) in all rooms being the elevated pollutant source above the viaduct compared to those without the viaduct. Road barriers on the viaduct slow down the flow above it and slightly increase indoor <K>, but they reduce indoor PN due to the enhanced particle deposition onto viaduct surfaces. The uniform heating of street ground or viaduct ground surface strengthens recirculation flows in street canyon, reducing <K> and PN of fine particle (diameter d = 1 μm), but for larger particles indoor PN distribution is complicated by the interaction of gravity, buoyancy and wind-induced recirculation. Although further investigations are still required to propose a practical framework on viaduct design, this paper is one of the first attempts to study the effect of viaduct on street pollutant dispersion.

This study analyses the effects of trees on local meteorology in a medium-size Mediterranean city (Lecce, IT) using field measurements and Computational Fluid Dynamics (CFD) simulations. Measurements were taken in two parallel street canyons with and without trees. Building façades and ground temperatures were estimated from infrared (IR) images, while flow and turbulence were measured by three ultrasonic anemometers. CFD simulations were performed by employing the Reynolds Stress Model (RSM). Overall the analysis shows that trees reduce the wind speed and alter the typical diurnal cycle of surface and air temperature within the canyon. In particular, the flow interaction with trees induces wind direction fluctuations below tree crowns and lower velocities which are expected to lead to larger pollutant and heat trapping in the lower part of the street canyon, especially in nocturnal hours.

This paper reviews recent findings in the field of flow and pollutant dispersion modelling around buildings and within complex urban geometries. Complexity is not only associated to the packing density of buildings, but originates also from building-height variability, buoyancy effects close to the building walls, traffic-produced turbulence and from the presence of vegetation. Recent results are discussed in light of progress made in operational urban dispersion models as a way forward for the application of those models in real scenarios.

This paper reviews recent studies pertaining to flow and pollutant dispersion around buildings and complex geometries (real cities). Field/laboratory experiments and numerical simulations (mainly Computational Fluid Dynamics, with attention to Large Eddy Simulation approach) performed by us as well as by other researchers who have looked at flow, turbulence, dispersion and ventilation around bluff bodies are considered. We attempt to review state of the art results considering that the urban complexity is not only due to the packing density, but also spatial building-height variability, thermal properties, the presence of vegetation. These findings are discussed in light of recent advances of operational urban dispersion models.

This paper reviews current parameterizations developed and implemented within Computational Fluid Dynamics models for the study of the effects linking vegetation, mainly trees, to urban air quality and thermal conditions. In the literature, passive mitigation via deposition is parametrized as a volumetric sink term in the transport equation of pollutants, while a volumetric source term is used for particle resuspension. The aerodynamics effects are modelled via source and sink terms of momentum, turbulent kinetic energy and turbulent dissipation rate. A volumetric cooling power is finally considered to account for the thermal (transpirational cooling) effects of vegetation. The most recent applications are also summarized with a focus on the relative importance of both aerodynamic and deposition effects, together with recent studies evaluating thermal effects. Those studies have shown that the aerodynamic effects of trees are stronger than the positive effects of deposition, however locally the pollutant concentration increases or decreases depending on the complex inter-relation between local factors such as vegetation type and density, meteorological conditions, street geometry, pollutant characteristics and emission rates. Unlike aerodynamic and deposition effects on pollutant dispersion which were also found in street far from trees, the thermal effects were in general locally restricted to the close vicinity of the vegetation and to the street canyon itself. Future requirements in CFD modelling include more in depth investigation of resuspension and thermal effects, as well as of the VOCs emissions and chemical reactions. The overall objective of this review is to provide the scientific community with a comprehensive summary on the current parameterizations of urban vegetation in CFD modelling and constitutes the starting point for the development of new parametrizations in CFD as well as in mesoscale models.

Le applicazioni della Fisica e dell’Informatica alla Biomedicina includono i sistemi di individuazione di patologie (CAD, Computer-Assisted Detection) basati sul trattamento di dati provenienti da esami diagnostici (in particolare ma non limitandosi alle immagini diagnostiche quali TC, RM, etc.), gli strumenti di ausilio alla chirurgia (realtà virtuale, telechirurgia), l’analisi e l’interpretazione di segnali di interesse biomedicale (per esempio segnali da elettroencefalogramma, EEG, o da elettrocardiogramma, ECG). Questo lavoro presenta una rassegna di applicazioni, in cui gli autori sono impegnati, dandone alcuni dettagli implementativi e discutendone brevemente i risultati. Le applicazioni si differenziano per il tipo di dati analizzati (serie temporali provenienti da misure EEG, oppure dati bi- o tridimensionali contenuti in immagini diagnostiche), per il distretto corporeo di intervento, le finalità, la patologia.

This chapter discusses the spatial distribution of air pollutants in cities in light of progress made by the scientific community in the field of flow and pollutant dispersion around buildings and within complex urban geometries. With the rate of urbanisation expected to increase in the next years, countries are forced to face challenges in addressing air pollution. Starting from the process of urbanisation and the problem of outdoor air pollution, the discussion focuses on main factors affecting flow and pollutant dispersion in cities. The dynamic of the urban atmosphere is sensitive to a large number of factors related to meteorology, building geometry and city density as well as to the presence of urban obstacles such as trees, parked cars and other barriers, buoyancy effects due to thermal exchanges at urban surfaces, traffic-induced turbulence and others. Some of them are reviewed here. The recent research towards unregulated pollutants, such as airborne ultrafine particles, which are considered to show higher health impacts compared with fine particles, is briefly addressed.

This paper is devoted to the study of the aerodynamic effects of trees on airflow and pollutant dispersion in urban street canyons. The dispersion of traffic-released pollutants in street canyons lined with trees is analysed by means of both wind tunnel experiments and Computational Fluid Dynamics simulations. Different tree planting and street canyon configurations are considered with a focus on the variation in the tree stand density and their implications on pollutant concentrations for several wind directions and aspect ratios. The concepts discussed in the paper can also be applied in practice. For example, we employ a similar methodology to investigate a complex urban site in Bari (Italy) where situations with and without trees are examined and numerical results are compared to field monitored data. The analysis of the results shows the crucial role of trees in dispersion modelling of urban areas.

The urban heat island (UHI) phenomenon may produce several cascade effects on citizens' health, energy consumption and air quality. Numerical modelling is recognised to be a powerful tool for the analysis of the UHI, although the question of which model to use (as implied in the 'fit-forpurpose' approach) much depends on the application and on the result of satisfactory validation against field measurements. In this paper, two different modelling approaches are applied, namely the integral-semi-Gaussian model ADMS-TH and the CFD-based model ENVI-met, to assess the UHI phenomenon in a city of south Italy (Lecce). Modelling results are validated against field measurements collected during summer 2012. The results suggest that the integral model has the ability of capturing the UHI cycle at city scale, while CFD modelling did not provide any substantial improvements in terms of local geometric effects on temperature distribution.

A new project called Reform of Education in Sustainability and Climate in Urban Environments (RESCUE) has started in October 2012 in collaboration with Glasgow Caledonian University (GCU, UK), University of Salento (UdS, IT) and Lahti University of Applied Sciences (LUAS, FI) as the coordinator. The rationale of the project was the need for advanced education for a new professional concerning urban issues and climate mitigation and adaptation. Our research reveals no similar programme exists at present in Europe [1]. The strengths of our partners are built up on the different professional viewpoints to the education: climate change research (UdS), urban sustainability and management (GCU) and communicative planning (LUAS). Rapid urbanization and urban sprawl are causing different scale challenges to climate adaptation and urban quality of life while understanding of these issues demands a new kind of professional education compared with earlier programmes. The project aims to provide a new model of Master education based on a needs assessment and involving of several stakeholders in partner countries as well as six associate partner universities. It will also create and run a pilot programme of continuous professional education (CPD) and learn lessons from it to shape and mould the eventual Master’s programme. The presentation will enumerate the results of a Needs Assessment seminar and several dissemination event to be held in Spring 2013. It is hoped the action will lead to a joint MSc degree, aiming at creating a new breed of professionals in the highly interdisciplinary field of urban sustainability and climate change. The proposed joint platform will use the latest communication and media technologies to enhance the up-to-date nature of the content and wider cross-border participation of staff and students, leading to a cutting edge, mobile study programme” [3]. The HEIs are integrating and developing their existing Master modules to combine a new set of interdisciplinary course with a strong virtual nature. The validation of the final programme will guaranteed by the Scottish Credit and Quolifications Framework (SCQF) aligned to the Bologna Process.

Breathability in dense building arrays with packing densities similar to those of typical European cities is investigated using laboratory measurements and numerical simulations. We focus on arrays made up by regularly spaced square buildings forming a network of streets with right-angle intersections. It is shown that breathability can be evaluated using building ventilation concepts (mean flow rate and age of air) and from vertical mean and turbulent fluxes quantifiable through a bulk exchange velocity. Mean age of air reveals that varying wind angles result in different ventilation, which we explain through mean flow streamlines and exchange velocity. For low wind angles (wind direction almost parallel to the axes of half of the streets of the network), vertical transfer and mean transversal transfers are at minimum and removal of pollutants is associated with mean longitudinal fluxes. Larger wind angles result in better ventilation due to an increase of transversal fluxes and vertical exchange. The latter, for which a formulation is derived, shows a non-negligible contribution of the mean flow which increases with increasing wind angle. Ventilation conditions can be further altered by small differences in the array geometry. These observations are useful for the development of simple urban dispersion models.

This study analyses the effects of trees on local meteorology of a Mediterranean City (Lecce, IT) using field measurements and computational fluid dynamics simulations. Measurements were collected for 51 days in a street canyon with trees to cover different meteorological and foliage conditions. Building façades and ground temperatures were estimated from infrared images, flow and turbulence measured by ultrasonic anemometers. In the case of approaching wind parallel to the street axis, trees induce large wind direction fluctuations below tree crowns and velocities up to about 80% lower than those at roof top. This, combined with the obstruction by tree crown, lead to lower ventilation in the bottom part of the street, especially during nocturnal hours, and to in-canyon volume-averaged pollutant concentration about 20% larger than in the tree-free case. Ignoring trapping effects of trees, as typically done in many air quality models, may lead to underestimation of ground level concentrations.

This study analyses the aerodynamic effects of trees on local meteorological variables through in situ measurements and Computational Fluid Dynamics (CFD) simulations. Measurements are taken in the inner core of a medium-size Mediterranean city (Lecce, IT) where two adjacent street canyons of aspect ratio H/W?1 (where H is the average building height and W is the average width of the street) with and without trees are investigated. Building façades and ground temperatures are estimated from infrared (IR) images, while flow and turbulence are measured through three ultrasonic anemometers placed at different heights close to a building façade at half length of the canyon. Tree crown porosity is evaluated through the Leaf Area Index (LAI) measured by a ceptometer. Numerical simulations are made using a CFD code equipped with the Reynolds Stress Model (RSM) for the treatment of turbulence. Overall, the analysis of measurements shows that trees considerably reduce the longitudinal wind speed up to 30%. Trees alter the typical diurnal cycle of surface and air temperature within the canyon, suggesting that in nocturnal hours the trapping of heat is more important than the power of passive cooling through evapo-transpiration. Comparative numerical simulations provide further evidence that flow velocity reduces in presence of trees and although the typical wind channeling observed without trees is still maintained, trees enhance the formation of a corner vortex leading to reverse flow at the openings of the street. The reduction of the exchange of momentum between the canyon and the atmosphere above, shown by the measurements in presence of trees is confirmed by numerical simulations.

This study numerically investigates the influence of different vegetation types and layouts on microclimate and air quality in residential districts based on the morphology and green layout of Nanjing, China. Simulations were performed using Computational Fluid Dynamics and the microclimate model ENVI-met. Four green indices, i.e., the green cover ratio, the grass and shrub cover ratio, the ecological landscaping plot ratio and the landscaping isolation index, were combined to evaluate thermal and wind fields, as well as air quality in district models. Results show that under the same green cover ratio (i.e., the same quantity of all types of vegetation), the reduction of grass and shrub cover ratio (i.e., the quantity of grass and shrubs), replaced by trees, has an impact, even though small, on thermal comfort, wind speed and air pollution, and increases the leisure space for occupants. When trees are present, a low ecological landscaping plot ratio (which expresses the weight of carbon dioxide absorption and is larger in the presence of trees) is preferable due to a lower blocking effect on wind and pollutant dispersion. In conjunction with a low landscaping plot ratio, a high landscaping isolation index (which means a distributed structure of vegetation) enhances the capability of local cooling and the general thermal comfort, decreasing the average temperature up to about 0.5 °C and the average predicted mean vote (PMV) up to about 20% compared with the non-green scenario. This paper shows that the relationship vegetation-microclimate-air quality should be analyzed taking into account not only the total area covered by vegetation but also its layout and degree of aggregation.

In this paper, the role of trees on airborne pollutant dispersion in a real neighborhood in Pamplona (Spain) is discussed. A Computational Fluid Dynamics (CFD) model is employed and evaluated against concentrations measured during the last part of winter season at a monitoring station located in the study area. Aerodynamic and deposition effects of trees are jointly considered, which has only been done in few recent studies. Specifically, the impact on NOx concentration of: (a) tree-foliage; and (b) introducing new vegetation in a tree-free street is analyzed considering several deposition velocities and Leaf Area Densities (LAD) to model deciduous and evergreen vegetation. Results show that the higher the LAD, the higher the deposition (concentration reduction) and the blocking aerodynamic effect (concentration increase). Regardless of foliage or deposition rates, results suggest the predominance of aerodynamic effects which induce concentration increases up to a maximum of 7.2%, while deposition induces concentration decreases up to a maximum of 6.9%. The inclusion of new trees in one street modifies the distribution of pollutant, not only in that street, but also in nearby locations with concentration increase or decrease. This finding suggests that planting trees in street with traffic as an air pollution reduction strategy seems to be not appropriate in general, highlighting the necessity of ad hoc studies for each particular case to select the suitable location of new vegetation.

Studies are still required to understand how rural/marine wind remove ground-level pollutants released uniformly in street networks of high-rise urban areas. The link between building height variability and pollutant removal process still remains unclear. Several idealized urban-like neighbourhoods made of 9-row and 18-row small-scale high-rise square arrays (building width B = street width W, building packing density λp = 0.25) were first numerically studied with a parallel approaching wind and neglecting thermal effects. Normalized pollutant transport rates and pedestrian purging flow rate were applied to quantify the contribution of pollutant removal by mean flow and turbulent diffusion and their net purging capacity. Results show that the prediction of isothermal turbulent flows agreed generally well with wind tunnel data. For 9-row arrays with building height variations (standard deviation of 0-57.1%) and the same average canopy height (H0 = 2.33W), pollutant removal mainly depends on mean flows. Larger standard deviations tend to induce better pedestrian ventilation. In comparison to small and large standard deviations, medium values of 14.3-42.9% may experience smaller purging capacity by horizontal mean flows but significantly enhance that by vertical mean flows. For arrays with uniform heights, lowering aspect ratios (H/W = 2.33 and 2.67-1.5) or increasing street lengths (9-row to 18-row) may enhance the contribution of removing pollutants by turbulent diffusions across canopy roofs which may be similarly important as that by mean flows. Although further investigations are still required, this paper clarifies the relationship between building layouts, height variability and removal potential of ground-level pollutants in high-rise urban-like geometries.

This paper discusses the performance of the temperature perturbation-type ADMS-Temperature and Humidity Model (ADMS-TH) and the Computational Fluid Dynamics (CFD)-based model ENVI-met for the prediction of urban air temperature using measurements collected in the city of Lecce (IT) in summer 2012. The goal is to identify the most important factors influencing numerical predictions. Direct comparisons with measured data and statistical indices show that modelled results are within the range of acceptance. Daily trends are well captured although an underestimation of maximum temperature is observed. In ADMS-TH this is due to an underestimation of sensible heat fluxes during daytime, while in ENVI-met it can be attributed to an underestimation of turbulent momentum and thermal diffusivity. Overall, ADMS-TH did predict the temperature cycle with higher accuracy than ENVI-met and its performance was particularly good during the night. ENVI-met required an ad-hoc tuning of surface boundary conditions to predict nocturnal cooling, satisfactorily.