High-resolution impacts of green areas on air quality in Madrid

Abstract

This study numerically investigates the influence of trees on air quality in Madrid urban area (Spain). Simulations are performed using the mesoscale model WRF/Chem (EPA, US) and the microclimate computational fluid dynamics (CFD) model PALM4U (IMUK, DE) configured as LES (Large Eddy Simulation). PALM4U is running over one of the 1 km × 1 km grid cells with 5 m very high spatial resolution using three different scenarios. In the simulation domain, there is a zone (approximately 25% of the domain) of vegetation where the dominant species are broadleaf trees included in the BAU (Business as Usual) scenario. The second scenario is focused on changing the type of the tree from broad leaf at BAU scenario to needle leaf the so-called ND scenario and the third scenario called NOTREE which comprise the replacement of the trees located in the green zone. The base simulations (BAU) are compared with data from the Madrid air quality monitoring network for the evaluation of the simulation results. The effects of the trees are calculated comparing scenarios (BAU-NOTREE and BAU-ND), so a brute force methodology has been used. This paper shows that the effects of the trees and type of trees are not uniform across the urban area because there are variations in the energy fluxes and the aerodynamic effect and there are important interactions of trees with wind flow dynamics. The mitigation potential effect of trees on gaseous air pollutants concentrations is showed and also may enhance substantially air pollution in other areas.