A report on Trees and Urban Air Quality released by the Woodland Trust today, and produced in cooperation with Lancaster University and the University of Birmingham, shows that despite air quality in the UK improving in recent decades, there remain serious health issues relating to air pollution, particularly in towns and cities.
Estimates indicate that air pollution reduces life expectancy in the UK by seven to eight months. Air pollution causes irritation of the lungs, can worsen lung conditions, and also affects people with heart conditions. According to the British Lung Foundation one in every seven people in the UK is affected by lung disease — almost 8 million people.
The problem is exacerbated by high summer temperatures, an increasing occurrence as we face greater frequency of extreme weather events. Prolonged high temperature can bring on heart or respiratory failure or dehydration, particularly amongst the elderly, very young or chronically ill.
Urban temperatures in summer are made worse by a lack of green space. Green space, and trees in particular, provide shade and reduce the ambient temperature through the cooling effect of evaporation of water from the soil and through plant leaves.
Urban trees also remove large amounts of pollution and improve urban air quality. Although some trees produce pollen which can affect a proportion of hay fever sufferers, the overall benefits of trees to air quality and respiratory health are overwhelmingly positive.
Columbia University researchers found asthma rates among children aged four and five was significantly lower in areas with more street trees. The UK has one of the world’s highest rates of childhood asthma, with about 15 per cent of children affected.
Planting in areas of high pollution, for instance ‘hotspots’ such as traffic junctions and traffic lights, will yield proportionately greater rates of pollutant removal. Trees planted in conjunction with understory plants to leeward of air pollution sources can maximise pollutant scrubbing by plants.
Despite the evidence that air quality can be improved by careful selection and siting of trees in urban areas, there is little evidence that urban greening projects take account of how air quality goals can best be achieved. Worse still, a lack of investment in the management of urban trees is undermining tree cover in urban areas.
Design for change
There are real costs in poor health associated with poor air quality – both financial and human costs. It is critical that we maintain existing urban trees and expand tree cover for the benefits it can bring to air quality and urban cooling. Evidence shows how we can improve the choice and siting of trees and other vegetation for air quality, but it require vision from those responsible for design and planning in our towns and cities.
We should live in green places and move around through green spaces. Instead of walking along pavements by busy roads, choking on the fumes and detritus of urban traffic, let’s make places where we can walk or cycle to school, or work, or the shops through parks and along green corridors with trees and plants – places where we can breath.
Mike Townsend, Communications and Evidence Adviser