An account of a recent workshop at the Museum of London on air quality and plants which help clean our air of pollutants.
On 17th March I attended a workshop at the Museum of London, run by Jennifer Gabrys of Citizen Sense, a research project investigating how to involve and engage the public in gathering environmental data. In the case of this workshop the focus was on how air pollution is measured, and how planting can be used to control and reduce the harmful effects of air pollution.
After a short introduction we were led on a walk (very brisk due to the cold weather!) around the Barbican estate to see a variety of ‘clean air gardens’ which have been created as part of the project. These are miniature urban gardens – generally either a single raised bed or a collection of containers – which have been installed in strategically chosen locations (for example as a screen between residential areas and a heavily polluted road) and planted using species which can absorb pollution.
We then returned to the museum’s seminar room to discuss and share ideas on how to develop a ‘toolkit’ which will be made available to community groups, local authorities and others to help them develop their own pollution-mitigating gardens.
Landscape architect Paul McGann explained the difficulties of caring for plants in urban areas. For example, of all new street trees planted in London almost a third do not survive their first year. The main hazards are:
- compaction of soil around the roots (by traffic, hard landscaping)
- salt poisoning (caused by gritting of roads and pavements in winter)
These particular challenges of the urban environment should be taken into account when choosing plants, in particular for roadside locations.
The ‘toolkit’ being put together as part of the project includes a list of specific plants which can absorb and store pollution, either by capturing particulates and nitrogen dioxide through the leaves, or by taking up heavy metals from the soil. (The pollutants are stored by the plant but then released into the soil when the plant dies.)
The plants mentioned as being useful included:
- Silver birch – cleans the soil by taking up heavy metals, and the air by trapping particulates (both PM10 and PM2.5).
- Juneberry/serviceberry (amelanchier lamarckii) – captures particulates and nitrogen dioxide, and is a good small tree beneficial to wildlife.
- Yew (taxus baccata) – can be used to create evergreen screens by roadsides to trap air pollution.
- Dwarf mountain pine (pinus mugo) – like the yew, can trap significant amounts of airborne pollutants due to the large surface area of the needles.
- Aster – absorbs lead, selenium and cadmium from the soil as well as trapping particulates.
- Yarrow (achillea millefolium) – the leaves capture particulates (both PM10 and PM2.5)
- Lady’s mantle (alchemilla mollis) – can reduce levels of both particulates and nitrogen dioxide. Also a good source of nectar and pollen for insects.
- Wallflower (erysimum) – captures particulates, and also attractive to pollinating insects.
- Euphorbia – takes up lead and arsenic from the soil, as well as absorbing particulates and nitrogen dioxide.
- Common ivy – where used over large areas such as green walls, very effective in absorbing air pollution.
- Heuchera – traps both particulates and nitrogen dioxide.
- Lavender – again, effective against both particulates and nitrogen dioxide.
- Woodland sage (salvia nemorosa) – beneficial to pollinating insects as well as removing pollutants from the air.