Air pollution – hedgerows can help

A sobering new report from the Lancet Commission on Pollution and Health cites pollution as the largest environmental cause of disease and premature deaths, responsible for 16% of all deaths worldwide and in Britain, for 50,000 deaths a year. Air pollution contributes significantly to this health crisis, estimated by the Royal College of Physicians and the Royal College of Paediatrics and Child Health to cost more than £20 billion per annum, for business from illness and the cost to the health service.

There is an intense debate around the urgent action needed to tackle the sources of pollution at source, including encouragement of financial incentives towards cleaner vehicles, setting up a ‘clean air fund’ to support local authority action on pollution and changing individual’s attitudes to cars.  Whilst such preventative action is essential, so also are different approaches to urban design.

Green Infrastructure

Use of simple and low-cost design features in new development, and planting new habitat features close to highways and other pollution hotspots, has direct beneficial effects on air quality.  Different ecological features offer different effects on pollution levels, and the strategy should therefore be tailored to the specifics of each scheme.  Research published by iSCAPE in May 2017, for example, shows that low hedges reduce exposure to harmful pollutants from vehicle emissions by trapping exhaust releases at ground level. This simple urban design approach is far more effective than taller street trees which, like tall buildings, can create a canyon effect that prevents dispersal of pollutants.

This is not an argument for removing existing trees, nor for avoiding planting new roadside trees.  Cities need green infrastructure for many reasons and, in any new greening, trees have an important role to play, for visual amenity, flood management, ecological connectivity, physical separation of areas and psychological benefit. They also reduce pollution levels more effectively than hedges in less built up urban environments.

The London Infrastructure Plan 2050 is one of the few in the UK which acknowledges that green infrastructure must be considered as an integral part of the city’s vital systems, as essential as the city’s transport, energy, water, waste and digital infrastructure. The London Plan specifically acknowledges the role of vegetation, and especially trees, to improve air quality by trapping particulate matter (PM) and absorbing polluting gases, such as nitrogen dioxide (NO2).

Design for air quality benefit

Intelligent and well-informed use of urban design tools can create significant local variation in the distribution and absorption of pollutant concentrations. The ‘palette’ of approaches, whether tree and shrub or hedgerow screen planting, green roofs, walls, roof terraces and roof gardens, recreation routes and pocket parks, all have a part to play – in the right place.  They also contribute to other ecosystem services of proven social and economic value, including rainwater and microclimate regulation, biodiversity enhancement, and health benefit.

Going Forward

Air quality controls are already in place in areas where local authorities declared Air Quality Management Areas (AQMAs) because air quality objectives are not, or are unlikely to be, met and national planning guidance already requires planning authorities to use planning conditions and obligations in new development to avoid unacceptable risks.

It is no more than sound planning to use design to address this need.  If you need further information on using green infrastructure in urban design, please contact Andy Spargo or James Sleigh on 0117 9230455

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