| Summary: | Traffic-generated particulate matter (PM) air pollution remains a serious threat to human health and the environment. Whilst the ability of vegetation to reduce PM pollution is widely recognised, little or no information is available on the value of living walls in this respect. This thesis explored their potential to serve as near-road/rail PM filters, and evaluated the optimal conditions required to maximise their PM capture efficiency, using both field and laboratory-based techniques. This study revealed living walls could immobilise substantial levels of PM associated with both road and rail traffic. Of three living walls studied, one, located along a busy road, was shown to remove substantial levels of PM1 (122.08 ± 6.9 x 107) and PM10 (4.45 ± 0.33 x 107) per 100 cm2; the highest level of PM2.5 removal (9.9 ± 5 x 107) was recorded from a wall located near a busy train station. The best PM-removing species, and the important leaf traits, were identified using living wall plants and natural/synthetic leaf models. There was a considerable inter-species variation in PM accumulation and the PM densities on some species were x50 and x65 higher compared to others. The influence of leaf size on PM accumulation was found to be dominant over other examined characters (leaf size, shape, and micromorphology); smaller leaved species with a high Leaf Area Index were identified as the most efficacious. Analysis of captured PM from rail and road traffic showed the ability of living wall plants to immobilise a wide range of elements which are known to be hazardous to health. Simulated rainfall demonstrated the potential for rain to wash particulates off leaves and renew capture surfaces to ensure their continuous functioning; wash-off removed between 48.4% and 92.5% of particles depending on the species. An impact of planting design on the PM reduction performance of living wall species was demonstrated by the superior capture efficiency resulting from increasing the topographical heterogeneity of plantings. This research enhances our understanding of the benefits of living wall systems in relation to PM pollution mitigation, and consequent improvement of human wellbeing.
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