Can Plants Save London's Air? The Power of Urban Greening in Combating Air Pollution

Air pollution is a pressing environmental concern, and the public is increasingly aware of the risks it poses. With the rise of urbanisation and industrialisation, nearly 90% of people worldwide live in areas where the air is classified as hazardous by the World Health Organization. This alarming statistic calls for immediate action to address the health issues caused by air pollution, ranging from respiratory diseases to developmental disorders and cancers.

Recently, green infrastructure - the integration of plants into urban areas - has gained traction as a potential mitigation method for air pollution.  As well as improving the balance of Carbon Dioxide and Oxygen in the air, plants are capable of removing, and dispersing airborne pollutants, and so are a potentially useful tool for improving air quality. By integrating plants and green infrastructure into cities, we can improve air quality and create healthier environments for everyone. In this blog post, we will explore the question: Can plants help make London's air safe to breathe?

Understanding Air Pollution in Urban Areas

What is air pollution, and why are urban areas particularly affected?

Air pollution is an umbrella term to describe airborne substances that are damaging to human health. The sources of these pollutants are almost always linked to human activities such as industry and transport - cars, motorbikes, and trucks are by far the biggest culprit from their exhaust fumes and tyre and brake degradation. The structure of urban spaces then compounds the problem by trapping these emissions between buildings, creating ‘street canyons’ that cause highly polluted roads and roadside spaces. This means that cities are very vulnerable to the problem and now the air in urban spaces is very often hazardous to people.

The Power of Urban Greening

What is urban greening, and how can it contribute to improving air quality?

Urban greening involves the integration of green spaces, vegetation, and plant-based infrastructure into urban environments. It encompasses various elements, including parks, green roofs, living walls, parklets, sustainable drainage systems (SuDS) and custom planters. These green interventions play a crucial role in mitigating air pollution and creating healthier cities.

Plants have the remarkable ability to absorb airborne pollutants and release oxygen, thus improving the balance of gases in the atmosphere. Trees, for example, act as natural filters, removing pollutants and particulate matter from the air. Additionally, living walls and green roofs can help reduce pollution by capturing and filtering pollutants before they enter the air.

It is not, however, as simple as just putting plants into an area. As a large diversity of compounds contribute to air pollution, there is no one plant type that can combat them all. Instead, species must be utilised for their anatomical and physiological features to combat plants that are suited to the removal of specific pollutants - and so plants must be used intelligently in an area to maximise the impact of green infrastructure on air pollution.

The Role of Trees in Air Quality Improvement

How do trees contribute to making London's air safer to breathe?

Trees are among the most effective tools in combating air pollution and improving air quality. They not only filter pollutants but also provide shade, reduce noise, and enhance the overall aesthetics of urban areas. In London, trees are estimated to remove around 2,000 tonnes of air pollution each year, equivalent to the emissions from taxis in central London.

Proper tree placement is crucial to maximise their air purification capabilities. Trees strategically positioned near roads and in areas with high pollution levels can help disperse pollutants and reduce their concentration.

Moreover, trees enhance the urban greening factor, which refers to the amount of vegetation and greenery in a city, thereby creating a healthier and more sustainable environment.

Innovative Solutions for Urban Air Quality Improvement

What are some innovative solutions that utilise plants to combat air pollution in London?

Apart from trees, several other innovative solutions are being implemented to improve air quality in London:

1. Living Walls are vertical structures covered with vegetation that bring nature to urban environments. They offer numerous benefits in the fight against air pollution in London. Living walls act as natural air filters, trapping and removing pollutants from the surrounding air. Their lush greenery enhances the urban greening factor and adds visual appeal to buildings. Living walls also contribute to temperature regulation and reduce energy consumption by providing insulation and shade.

2. Parklets, another innovative concept, involve converting small sections of parking spaces into green areas. They create pockets of green amidst the concrete jungle, offering a respite for pedestrians and cyclists while reducing pollution levels. Parklets provide a space for relaxation, socialising, and enjoying nature, all while combating air pollution.

3. Rain gardens combined with Sustainable Drainage Systems (SuDS) are innovative solutions for managing rainwater runoff while combating air pollution. These gardens are designed to capture and filter rainwater, preventing it from entering water bodies and reducing the pollutants carried by runoff. By creating natural filtration systems, rain gardens with SuDS help remove contaminants and improve water quality. This, in turn, contributes to better air quality as the pollutants that would have entered the water bodies and potentially evaporated back into the air are effectively filtered out.

4. Green Screens are walls of planting that act as a blockade to trap or disperse pollution. Most often we utilise English ivy (Hedera helix), as it is exceptionally well suited to this role, this is due to its rough leaf texture that increases the capacity for capturing airborne particles, and its high leaf density that allows it to easily form an effective barrier. Through collaboration with the Mayor of London’s Greener City fund, we have installed them to protect the playgrounds of many Primary Schools that bordered busy roads.

   A study by Kings College found that the installation of green screens in a school playground bordering a busy road reduced the levels of two of the most prevalent and dangerous pollutants, Nitrogen dioxide and microscopic particulate matter, was reduced by 36% and 41%, respectively, inside the playground.

Plant Benefits Beyond Air Quality Improvement

Are there other benefits of plants and green infrastructure beyond air quality improvement?

The benefits of plants and green infrastructure extend far beyond air quality improvement. Greenery has a positive impact on mental health and well-being, creating a connection with nature and reducing stress. This concept, known as biophilia, recognises the innate human need for contact with nature. Biophilic design, which incorporates natural elements into the built environment, promotes human health and productivity.

Green infrastructure also plays a significant role in biodiversity conservation, providing habitats for wildlife in urban areas. Additionally, green spaces enhance the livability of cities, offering recreational opportunities, promoting physical activity, and fostering a sense of community.

Conclusion

Urban greening and the integration of plants into London's landscape offer tremendous potential for improving air quality and creating healthier environments. Trees, living walls, green screens, parklets, SuDS and other green infrastructure solutions contribute to air pollution mitigation, enhance the urban greening factor, and provide numerous additional benefits such as mental well-being, biodiversity conservation, and livability.

At Meristem we have been at the forefront of intelligently utilising plants to provide the infrastructure that delivers a wide multitude of services, from ecological pollinator support to stormwater management.

However, green infrastructure cannot stand alone as the solution to improving urban air quality. Despite its impact, it is very much a mitigation method, and it needs to be applied in conjunction with reducing the sources of pollution. The Ultra Low Emissions Zone (ULEZ) in London is a significant step in the main source of pollution in cities, by reducing the number of cars present, pedestrianisation is also an important part of the fight, and the greening of pedestrianised streets using vegetation barriers and large planting can create a green and clean space in cities for people to enjoy without jeopardising their health.

By embracing the power of plants and biophilic design, we can pave the way for a greener, cleaner, and more sustainable city for generations to come.