The Impact of Planting Trees on NOx Concentrations: The Case of the Plaza de la Cruz Neighborhood in Pamplona (Spain)

Abstract

Abstract: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 NO x 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.

Designing vegetation barriers for urban air pollution abatement: a practical review for appropriate plant species selection

“…A higher vegetation barrier density generally results in lower downwind concentrations of both PM 86,98,99 and gaseous pollutants 54,100 . However, CFD modelling undertaken by Ghasemian et al 54 found that a LAD of 3.33 m 2 /m 3 reduced downwind concentrations of roadway emissions (represented by a tracer gas) by 10%, whereas a LAD of 1 m 2 /m 3 increased downwind concentrations by 15%.…”

The Impact of Green Space Layouts on Microclimate and Air Quality in Residential Districts of Nanjing, China

“…Thus, the pollutant accumulated within the street canyons is closer to the pollutant source upwind with poor pollution transport downwind. The ventilation gets worse in the presence of vegetation as the concentration distribution suggests that the aerodynamic effect seemed to prevail over the filtering capacity [18][19][20][21][22]. To further show the effect of vegetation on pollutant dispersion, as an example Figure 16 shows that, for Case A, the area where the PM10 concentration is below 10 µg/m 3 almost accounts for 64% and the maximum PM10 concentration in the residential district is about 50 µg/m 3 .…”

“…The deposition of particles on vegetation surfaces can be influenced by various factors, such as the diameter and shape of the particles, the planting configuration and meteorological parameters. Although the deposition on vegetation helps to remove particles from the air [15][16][17][18], the aerodynamic effects may reduce the air exchange compared with a no-green scenario, reducing mixing, dilution and ventilation [18][19][20][21][22].…”

Experimental Validation of a Numerical Model of a Ventilated Façade with Horizontal and Vertical Open Joints

“…CFD models are specially designed to evaluate convective processes in buildings by solving the Navier-Stokes equations, since ventilation flows are complex [16]. These models are widely used to model indoor and outdoor airflows [17,18], heat transfer [19,20] and contaminant transport [21].…”