Air pollution is the presence of substances in the air that have harmful or poisonous effects, for people, wildlife and the environment. It can have a serious impact on our health, but there are ways to improve pollution levels. Trees have a key role to play.

A report from the World Health Organisation (WHO) shows that 90% of people on Earth live with poor or even dangerous air quality. Although air quality in the UK has improved in recent years, many UK cities continue to exceed safe limits for harmful particulates and oxides of nitrogen (NOX). The WHO recommended limit for levels of PM2.5 particles in the air is 10 micrograms/m3, but dozens of UK towns and cities are over this limit, including:

  • London (11)
  • Liverpool, York and Nottingham (12)
  • Salford and Scunthorpe (15)
  • Port Talbot (18).

The best air quality tends to be in more open areas and coastal areas, where the air changes more frequently. You can check the daily air pollution forecast for where you live on Defra’s website.

Living with poor air quality

In the UK, around 40,000 deaths annually are linked to air pollution. Poor air quality is principally linked to heart and lung conditions, but can also be associated with other problems such as cancer. A calculation of the cost to society in terms of people who suffer from illness and premature death, and costs to health services and business, suggests this could be more than £20 billion a year.

The UK has one of the highest rates of childhood asthma in the world. A study in Bradford city, published in March 2018, showed that around 38% of childhood asthmas were attributable to poor air quality, specifically levels of NOX, and that much of this was from traffic related pollution. Research has found significantly lower asthma rates among children aged four and five in areas with more street trees.

Health problems are exacerbated by high summer temperatures, an increasing occurrence as we face greater frequency of extreme weather events. Prolonged high temperatures can bring on heart or respiratory failure, particularly amongst the elderly, very young or chronically ill.

The importance of trees

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 can also remove pollutants and improve urban air quality. Although some trees produce pollen which can affect hayfever sufferers, the overall benefits of trees to air quality and respiratory health are overwhelmingly positive.

Planting in areas of high pollution, for instance 'hotspots' such as traffic junctions, will yield proportionately greater rates of pollutant removal.

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 the best way to achieve air quality goals.

Worse still, a lack of investment in the management of urban trees or the removal of trees on grounds of health and safety is undermining tree cover in urban areas.

Design for change

There are real costs to health associated with poor air quality. It is critical that we maintain existing urban trees and expand tree cover for the benefits it can bring. This requires 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 breathe.

What can I do?

You can help improve air quality by getting involved in planting activities, asking your council to plant more trees, and importantly, by defending the ones we already have. 

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