Microscale CFD Evaluation of PCS Impacts on Air Quality Deliverable 6.2 iSCAPE project

Air pollution continues to be a global concern among the scientific communities due to its impacts on human health, the environment and climate change. Due to the specific urban landscape and climatic characteristics in European cities, passive control solution (PCS) has been selected for analysis by Improving the Smart Control of Air Pollution in Europe (iSCAPE) project. PCSs include low boundary walls (LBWs), trees and hedges, green walls and green roofs, photocatalytic coatings, green urban spaces and road geometry interventions. The effect of trees, green roofs and green façades in the real urban environment on pollutant concentration at street level has been carried out in Bologna. The Guildford living lab focuses on hedges in open-road environments unlike other cites simulating street canyon conditions. The Dublin study focused on determining the effectiveness of LBW passive control structure to reduce personal exposure to vehicular pollutants. The iSCAPE project aims at altering the dispersion mechanism, enhancing the deposition process and chemically breaking down the air pollutants in order to reduce their concentration levels at target receptors by using PCSs. Although practical implementation of PCSs needs to be supported financially, the application of inexpensive tools, such as computer programming is always demanded. A detailed analysis of two street canyons (with and without trees) in Bologna has been considered in two days cycles, covering the summer and winter seasons. The results show that planting trees within street canyons without trees (aspect ratio > 1 and traffic intersections) give more uniform distribution, but pollutant concentration levels could be higher than expected in some zones. On the contrary, non-uniform distribution in space pollutant concentrations, especially near the intersections within street canyons without trees have been observed. Additionally, the application of green roofs and green façades modifies the flow field at street level and the pollutant near the building walls. The study in Guilford showed that the hedges along the street work as a barrier for the pedestrians as validated by the experimental results. The hedge grows increases wind speed at the breathing level (1-2 meters) forcing pollutants to move along the road. The calibrated CFD model for wind speed/direction and NO emission in Dublin was used to determine the effect of implementing a LBW in pollutant concentrations on the footpaths. The model included LBWs along both sides of the canyon with gaps for road junctions and bus stops. Both reduction and increase in pollutant concentrations on the footpaths in parallel and perpendicular wind models have been reported. The purpose of this deliverable (D6.2) is to document findings from simulation studies on the detail effects of PCSs on neighbourhood air quality in three different iSCAPE cities (Bologna, Guildford and Dublin). The development and testing of new PCSs and their effects on local air pollution and climate have been assessed through the computational fluid dynamic (CFD) simulations (task 6.2 of the work package, WP, number 6). Field measurement data collected as a part of the iSCAPE project (WP5) is used for validation of the model simulations. The output of this deliverable addresses simulating effects of infrastructural solutions on air quality at neighbourhood levels that are discussed in WP6.2