Review on urban vegetation and particle air pollution – Deposition and dispersion

TLDR

Urban vegetation influences air quality by affecting pollutant deposition and dispersion, yet experimental data on key parameters are lacking, making design choice critical for effective air‑quality improvement. Effective filtration barriers must balance density for deposition surface area with porosity for airflow, and the choice of vegetation height and density determines impacts on different particle sizes and sources. Adding large trees to trafficked street canyons reduces mixing and raises local pollution, whereas low vegetation near sources enhances deposition and improves air quality.

Abstract

Urban vegetation affects air quality through influencing pollutant deposition and dispersion. Both processes are described by many existing models and experiments, on-site and in wind tunnels, focussing e.g. on urban street canyons and crossings or vegetation barriers adjacent to traffic sources. There is an urgent need for well-structured experimental data, including detailed empirical descriptions of parameters that are not the explicit focus of the study. This review revealed that design and choice of urban vegetation is crucial when using vegetation as an ecosystem service for air quality improvements. The reduced mixing in trafficked street canyons on adding large trees increases local air pollution levels, while low vegetation close to sources can improve air quality by increasing deposition. Filtration vegetation barriers have to be dense enough to offer large deposition surface area and porous enough to allow penetration, instead of deflection of the air stream above the barrier. The choice between tall or short and dense or sparse vegetation determines the effect on air pollution from different sources and different particle sizes.