VEG-AIR

Vegetation and urban air quality: CFD evaluation of vegetation effects on pollutant dispersion

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 Obiettivo del progetto (Objective)

'Air quality in the urban environment is gaining increasing attention by city authorities and residents due to rising urbanization and growing individual traffic. One important aspect in today's urban design and planning is to make cities favorable for the natural ventilation enabling a fast dispersal and removal of air pollutants emitted by traffic and buildings. Green spaces play an important role in these considerations as they may enhance, e.g. by wide open parks, or inhibit, e.g. by avenue-like tree plantings in urban street canyons, the natural ventilation. The influence of vegetation on pollutant dispersion and concentrations in the urban environment will be investigated by Computational Fluid Dynamics (CFD) employing Reynolds-averaged Navier Stokes (RANS) turbulence models and Large Eddy Simulations (LES). A central point in this research project is to develop new parameterizations (vegetation modules) accounting for the effects of vegetation on flow and turbulence characteristics. The CFD simulations will be evaluated against available wind tunnel data, e.g. the CODASC database (Concentration Data of Street Canyons, www.codasc.de), wind tunnel studies to perform at collaborating institutions and full scale experiments in the Dutch cities of Arnhem and Nijmegen (leader of these street case studies: Dr. ir. Bert Blocken, TU Eindhoven, period 2011/12). The project's outcomes will strongly contribute to an improved air quality modelling in the urban environment by taking the important implications of vegetation on flow and turbulence characteristics into account. CFD simulations are becoming gradually more important in urban air quality modelling with increasing computer performance in the next years. Therefore, validated CFD models with vegetation modules will become an indispensable tool for considerably improved predictions and assessments of urban air quality, to achieve an overall better, healthier and more comfortable living environment.'

Introduzione (Teaser)

Researchers have modelled and evaluated different urban greening practices for their ability to influence air pollution and decrease temperatures in cities.

Descrizione progetto (Article)

Air quality and urban heat islands in European cities are a growing concern as more and more of the population relocates to urban areas. Different configurations of avenues, roof gardens and green facades may be able to influence air quality and reduce air temperatures in cities.

To test this idea, the EU-funded 'Vegetation and urban air quality: CFD evaluation of vegetation effects on pollutant dispersion' (VEG-AIR) project developed improved models on the influence of vegetation on airflow and temperature in urban areas and provided some first guidance to urban planners.

The project first investigated the effects of avenue trees on ventilation and air pollution. It did so by testing various airflow models against experimental data. This part of the project identified one model that was the most accurate. Using this model, researchers showed that avenues of trees limited airflow and overall increased the concentration of airborne pollutants.

VEG-AIR also examined whether different greening measures had an effect on air temperatures in cities during hot summer days. Avenue trees reduced urban air temperatures the most, while green facades had a small effect and roof gardens did only negligibly affect temperatures.

These results show that using urban greening to improve air quality is far from straightforward. The implications of greening on the urban microclimate are manifold and complex. Nevertheless, the work of VEG-AIR has taken important steps towards using vegetation as an air remediation strategy.