The enhanced understanding of the symbiosis between urban planning, traffic
dynamics and local air quality is a needed goal towards the ultimate objective of promoting
healthier and sustainable cities. This chapter is focused on the most powerful tool currently
available for the assessment of air quality at the street-scale (i.e., at the pedestrian level): the
Computational Fluid Dynamics (CFD) models. A brief overview of the numerical concept
applied in the simulation of turbulent flows and dispersion processes is given. Major
questions in the CFD modeling of urban environments are highlighted: the role of vehicle
emissions estimation, the contribution of background concentrations to local air quality levels,
and the capability of these tools to assess the impacts of urban planning strategies and
scenarios. Examples of the application of a CFD model to real urban cases are given for the
cities of Lisbon (Portugal) and Helsinki (Finland).
Keywords: Urban environments, urban planning scenarios, road transport
emissions, emission control measures, emission modeling, air pollution, urban air
quality, urban sustainability, pedestrians exposure, Computational Fluid Dynamics
(CFD) models, fluid dynamics, Reynolds-Averaged Navier-Stokes Equations, data
analysis in frequency domain, Kolmogorov-Zurbenko (KZ) filter, exhaust emission,
emission factor, background concentrations, turbulence modeling, vegetative
canopies, air pollutants dispersion.
