Abstract
Green infrastructure (GI) is a potential solution to improve air quality in urban environments. The impact of GI on air quality in micro-environments depend on the extent and complexity of structures at the location as well as GI specific characteristics such as canopy density, species, and leaf features. To assess the benefits of GI, the suitability of various types in micro-environments must be evaluated. The outcomes of these studies expand on existing knowledge of GI effects on air quality, and must lead to GI implementation to reduce exposure and improve public health situated close to roads. This work started with a comprehensive literature review to identify gaps in current knowledge. Field campaigns assessed the air pollution reduction of different types of GI and quantify particulate matter (PM) reduction and their deposition on the leaves of GI. Follow-up investigations evaluated respiratory deposition doses (RDD) in the presence of different GI types. The hedges and hedge-tree combinations displayed the highest PM reduction in open-road environments. GI was found to be more effective in reducing exposure when winds are parallel to the road. GI also reduced traffic-originated elements in the ambient air behind them. Furthermore, PM deposition on leaves varied across sides of hedges. The majority of traffic-generated PM were captured on leaves facing traffic. In addition, the study revealed that GI is effective in reducing inhaled doses and recommends planting GI along the boundaries of public parks and recreational areas. The highest reduction in RDD was observed with a tree-hedge combination. The findings were used to develop preliminary guidelines for GI design to reduce air pollution in urban environments. GI recommendations address common people, governing authorities, city developers, traffic planners, and the scientific community. Multilevel implementation can be achieved from authorities adopting existing air pollution management policies to citizens modifying garden design.