Living Walls: How they Boost Air Quality and Reduce Pollution
What's a Living Wall?
Living walls are vertical systems of growing plants which can cover large surfaces of structures and buildings. Forest of Hearts living walls are modular and allow for a variety of plants to put into panels before being transported to sites, e.g. Warwick Hospital.
They provide a wealth of environmental benefits, especially if they contain a diverse array of plant species, such as cooling and insulating buildings, improving urban biodiversity, shielding building façades from weather damage, and reducing air pollution.
Air Pollution
An estimated 92% of the world's population are living in areas where air pollution is higher than the World Health Organisation's standards (WHO, 2014)
An estimated 9 million premature deaths globally will be caused by air pollution over the next 4 decades (OECD, 2016)
In the UK, the main pollutant concerns are particulate pollutants, oxides of nitrogen (NOx), ozone, and ammonia
An estimated 40,000 deaths are caused by outdoor air pollution in the UK, and 29,000 of those are caused by particulate matter pollution (RCP, 2016)
Particulate Matter (PM)
PM pollutants are detrimental to health, reduce atmospheric visibility, alter the radiative properties of the atmosphere, change the thermal environment, and influence the climate
Approximately 50% of PM in Europe is considered to be generated by road traffic. Traffic-generated PM is considered the most toxic class of PM (WHO, 2005)
PM has been classified as the most harmful air pollutant to human health (WHO, 2014)
What Plants Are Best at Trapping PM?
Smaller-leaved species have been shown to have a high particulate matter removal potential, e.g. juniperus chinensis (Chinese juniper) and hebe albicans (white hebe)
Hairy-leaved species might be better at removing more hazardous air pollution, e.g. thymus vulgaris (garden thyme)
Species with palmately lobed leaves (where leaves spread radially from a point like fingers in a hand) also show a greater potential to capture and retain PM, e.g. hedera helix (common ivy)
Brambles on living walls have shown notable potential for capturing pollution
Planting Design
A design with topographical heterogeneity (a diverse arrangement) created by interspersing different plants with different heights has a higher positive impact on the ability of plants to capture PM than a design with plants of similar heights... so mix it up.
Plants that work best in living walls to reduce pollution (especially particulate matter) include:
· Thymus vulgaris (thyme)
· Juniperus chinensis (Chinese juniper)
· Veronica vernicosa (varnished hebe)
· Burberis buxifolia (box-leaved barberry)
· Berberis x media (barberry "red-jewel")
· Spiraea japonica (Japanese meadowsweet)
· Boxus sempervirens (common box)
· Hebe albicans (white hebe)
· Hebe x youngii (hebe "youngii")
