Turning over a new leaf: a plan for cleaner air

To tackle the problem of air pollution, particularly in urban areas, we need to improve our green infrastructure. In particular I am suggesting that urban hedges should be planted to reduce air pollution.

In the 2019 general election political parties competed in their pledges to plant millions of trees to combat climate change and to achieve Net Zero suggesting that there is political will to improve the UK’s green infrastructure. However, it was predicted that the scope for these planting initiatives was relatively low in urban areas due to lack of space and the cost. 99% of Londoners live in areas exceeding the World Health Organisation’s recommended guidelines for air pollution levels and the European Court of Justice ruled that the UK has broken legal limits on air pollution for a decade. Already one nine-year old Londoner has air pollution as a cause of death on their death certificate. There is a significant need to tackle the problem of air pollution and specifically in urban environments where there is a lack of green infrastructure to absorb air pollution, such as emissions from cars on busy roads.

A solution to the problem of air pollution is to plant and manage hedges in urban areas to create a dense filter to absorb air pollution at its source and to provide protection to those effected by air pollution. In particular urban hedges should be planted alongside high level sources of pollution, such as busy roads, and alongside areas frequented by people particularly vulnerable to air pollution, such as schools and in residential areas.

A recent study by the Global Centre for Clean Air Research suggests that trees are not effective at reducing roadside pollution at breathing height whereas hedges are. Unlike trees, hedges are able to trap air pollution at the level it is produced and provide a barrier at breathing level between the pollution sources and the person breathing. Simply brushing up against a roadside hedge will demonstrate the volume of dust and particulates that the mesh formed by the hedge’s leaves filters. Trees, on the other hand, can sometimes trap air pollution at street level as the mesh of leaves of trees can trap the air. Hedges are a more effective and immediate solution than trees as they are quicker to grow and take less long-term development planning than trees in terms of size and shape. Additionally, managed hedges are more suitable for urban environments as they can easily be shaped to the needs of urban spaces.

Beyond improving air quality and air pollution reduction, urban hedges have benefits such as carbon sequestration which would help contribute to UK Net Zero initiatives; they can improve biodiversity and can be a source of pollination support; they can help with water management and rainfall capture; and they can reduce soil pollution. Urban hedges can also have insulating properties and in summer can help keep air cool; they can also reduce wind speed in streets that have high buildings that create a wind tunnel. Some studies also suggest that urban hedges can reduce noise pollution. Depending on how they are implemented, for instance between a footpath and a road, urban hedges could provide pedestrians and possibly cyclists protection from cars and reduce traffic accidents by preventing pedestrians from jaywalking. Urban hedges can add aesthetic value to built-up areas that lack green spaces with some studies suggesting that there are psychological and mental health benefits associated with proximity to plants and green infrastructure.

Planting and maintaining urban hedges may also have the advantage of creating new jobs. These jobs would be green jobs and providing more technical skilled opportunities in urban areas while preserving the technical skills in hedge growing and maintenance that otherwise might be at risk of being lost.

In terms of the practical implementation of urban hedges as a policy, this is an active area of research with experts and academics already specialised in this issue who could consult on the best way to implement it as a policy. There is a growing field of research as to the most effective plants to be used as urban hedges. Consideration has already been paid as to which plants are the most effective at absorbing roadside pollution with the Royal Horticultural Society suggesting Cotoneaster franchetii. Other studies look at how issues like allergenicity can be managed. Thought will still need to be paid as to how to manage invasive species and prevent issues like excessive shading. There may be some areas with urban planning requirements, such as the need for driver visibility on roads, that prevents the policy being utilised in some areas or may cause it to take a different from, for instance plant boxes as opposed to hedges in the ground. However, at a minimum urban hedge can provide a great deal of benefit to schools, playgrounds, and community centres.

A concern might be the cost of urban hedges as a policy but in the long-term the monetary saving made by the reducing air pollution levels would almost certainly outweigh the initial start ups costs of urban hedges as a policy. The long-term running costs of urban hedges are likely to be low and these are costs that are already incurred in the countryside maintaining hedgerows and in cities maintaining trees and other green infrastructure so there is data that can be consulted to estimate a cost. Depending on the implementation of the policy it may also be the case that local community members would volunteer to help with the maintenance of urban hedges thereby reducing the cost. Ultimately, the improvement to public health and quality of life by reducing air pollution through this policy make the cost of the implementation and maintenance worthwhile.




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