green barrier of plants

Green barrier to reduce air pollution: Interview with Maria del Carmen Redondo Bermudez

Grantham Scholar Maria del Carmen Redondo Bermudez researches how green barriers can reduce air pollution. Her PhD project is focused on the use of plants as ‘living walls’ around playgrounds to improve air quality for children. 

Maria works out of the Department of Landscape Architecture, she also has supervisors from Geography, Animal & Plant Sciences, and Materials Science & Engineering. Now in the second year of her PhD, Maria was born and raised in Mexico City.

In this interview she talks about the green barrier, how people can make them in their own gardens, and why she has hope for a sustainable future.

Interview: green barriers and air pollution

You’re creating a green barrier to reduce air pollution. It sounds amazing – can you tell us more about it?

My project deals with a global problem – air pollution – in a site specific way. Air pollution is a problem here in Sheffield and around the world. It causes people to die before their time and is responsible for many health problems. It is especially bad for children because their organs are developing, particularly their lungs.

This project looks at ways to reduce the impact of air pollution on school children. We’re doing this by creating a living barrier of plants around 2 school playgrounds – in Sheffield at Hunters Bar and the other in Buenos Aires.

The green barriers project in Sheffield came about from a grass-roots movement, what happened?

It is amazing because it is totally grass-roots. Hunters Bar Infant School approached the University of Sheffield. They did this because air pollution was something the school felt they could do more about, but did not have the expertise and tools to act.

As a result of this approach, the University started the development of the green barriers project. When I came on board with the Grantham Centre I expanded it. For instance, the basic idea of the green barrier idea was present, but not how to do it or what species to use.

What is the green barrier made up of, what kind of plants are you using?

The green barrier has 3 main layers.

Firstly, there are climbers, such as ivy, all around the playground. The ivy can capture particles and reduce NO2, and they act as a physical barrier but are more permeable than a wall.

Then there are conifers and bamboo. These are plants that grow fast and provide a physical barrier to pollution, and can catch particulates (tiny particles of air pollution) on their leaves and bark.

Thirdly there is the aesthetic layer, which is important for helping people accept the green barrier. These are species that look good as well as having other desirable properties, such as leathery leaves to catch particulates. Or maybe they are pollinators, or they enhance human well-being. Or they’re chosen just because they enhance the design and harmonise with the key plants.

How does the green barrier stop air pollution?

Plants act as a physical and biological barrier to air pollution. For instance, particulate matter in the wind can be blocked by green barriers or tree canopies.

Further, particulate matter that passes through that kind of barrier will be deposited on leaves and bark. On some plants particulates can get embedded in waxes exuded by the plant. The particles then get washed away when it rains and the capacity of plants to capture more is replenished, to a certain extent.

What about nitrogen dioxide?

With nitrogen dioxide (NO2) – which is produced by car engines – it is different.

Plants absorb NO2 during their respiration process, which removes it from the atmosphere, and that decreases air pollution for us. But it damages plants. Whilst plants do need some nitrogen, too much will harm them. Acute concentrations of NO2 are related to a reduced chlorophyll content and causes stress to the plants.

Finding plants that are tolerant to NO2 is key for air pollution mitigation and knowledge of these plants is a gap in current scientific knowledge.

the school playground before
Maria and volunteers, including some from Henry Boot Construction, in the playground before the green barrier is installed.

What does it mean to say the green barrier is a ‘site specific’ response to air pollution?

This project will create the best green barrier for this specific context, not for every single situation, or even every school. Each context will need a different set up of the green barrier to be optimal.

For Hunters Bar, which is an infant school, it’s especially important to find plants that are not harmful, such as being poisonous or spikey. And because the children need the playground to play in, we have considered plants that can fit in a space of 1 to 2 metres wide.

Further, I have to take into account the characteristics of the space, like where the wind comes from, the rain conditions, and the location of the buildings around it.

It sounds like this project needs expertise from more than plant sciences?

Yes, I need more than natural science or even engineering to do this project. Engineering only deals with the abiotic (nonliving) part of the world. Whereas the environment is of course made of both abiotic and biotic (living) elements. And in this project we are introducing the biotic to solve a problem of the abiotic.

Social science comes in because we need to know that the barrier will be maintained and the knowledge will be passed on. And it is also important to understand the perception of the people involved in the project (school community, business, government, other stakeholders) for its validity and effectiveness.

What can people do in their gardens if they want to make their own green barrier to reduce air pollution?

Just add plants!

The best plants are those that have a large surface area to capture particulate matter. And conifers – anything with needle leaves – are perfect.

Plants with broad leaves that have grooves, crests or hairy leaves are also good because particulates get stuck in them.

a picture of a garden with lots of plants - if you want your own green barrier to reduce air pollution just add plants
What can you do in your own garden to combat air pollution? Just add plants!

Not everyone will know how projects like this work – can you tell us more about what you do?

My first move was a literature review (research into previously published work on a subject) to see what’s worked with other green barriers. From the review I gathered ideas for species and arrangements that fit best with this project.

Then the Department of Landscape Architecture and I partnered with the landscape architecture firm Urban Wilderness to complete the planting design.

We also work in collaboration with Henry Boot Construction, Arup and Ramm Sanderson, who provided expert advice and building materials. And Urban Flows, who provide air quality monitors.

Your project uses plants to fix a problem, which is a type of biotechnology. Can you explain a bit more about what biotechnology is?

Biotechnology is the use of living beings to solve any kind of problem. It can be any type of living thing, such as plants, bacteria or fungi.

For example, I did a project that used fungi to remove pigment from water contaminated by the clothes dying process. In another project I used bacteria to remove hydrocarbons from soil. These 2 projects inspired my future career.

However, the living barrier of plants to reduce air pollution is more of a ‘nature based solution’, where we are mimicking what happens in a natural ecosystem to adapt it to the city and provide the ecosystem service of air quality regulation.

Is biotechnology a big part of sustainable adaptation to the environmental crisis?

Yes and no. Plants, bacteria and fungi can do amazing things, they can help us to solve problems in a more natural way without harmful subproducts.

However, if we use plants in this way we must also provide a good environment for them. Living things are complicated, and they are easy to harm. We should be respectful when using them and in return they will help us to solve many problems

Also, there are also technological solutions that do not involve living beings which we should use alongside the biotechnological solutions.

I think that at this point of the environmental crisis, we should do everything and anything.

What is your motivation for working to reduce air pollution for children?

Maria standing near a busy road using her pollution measuring tool
Maria using a sensor to monitor air pollution on a busy road in Sheffield.

When I was in Mexico as a young kid there were big problems with air pollution. There were days I could not go out into the playground due to a government rule about air pollution exposure.

I remember clearly how being inside all day, not being able to go out and play, was horrible. I don’t want any children to experience this – and this keeps me motivated.

Are you hopeful about our chances with the environment?

My feelings are mixed. Sometimes it’s terrifying. On the other hand, you need to put limits around it, or it contaminates your life and then progress cannot happen. You have to have hope, it’s hard to do anything without hope.

However, it’s also true that unless there’s a catastrophe people won’t act. Because unless events relate to us in a close way we don’t act – that’s just how humans are. Of course there are some people who just don’t give a damn whatever happens.

Does it impact your personal life?

In my personal life I try to be mindful about the environmental situation and act daily. Every decision I make is affected by it. This can result in a bit of a guilty whirl! So I do try to be realistic and push not only for personal changes but for systematic and political changes.

Every human being should be doing what they can. I feel very lucky that my studies let me help in a direct way, but everybody can help from their own discipline and life.

Do you feel there’s pressure on your generation to fix it all?

Yes. A lot of pressure, or at least I feel it because I want to change things.

I especially worry about people having children. No one can guarantee there will be a safe and harmonious world for them to grow up in!

Being part of the Grantham Centre adds pressure – but also support. We are creating knowledge that might make a difference, and we acquire skills that enable us to make change. We get a lot of extra training here, which is great. Further, we influence in other ways. For instance, by doing outreach or being activists, which my colleagues in other departments don’t necessarily do.

What’s the one thing you wish everyone knew about sustainability?

I wish everyone knew that plants and greenery in cities provide multiple benefits to humans.

Plants can help with city cooling, reducing energy use, flood mitigation, enhancing biodiversity and – in the right scenarios – air quality improvement.

But greenspace also has a restorative effect on people.

For example, a walk in the park can help us focus better in our work. Just look at the growing trend of forest bathing (a prescribed walk in the woods or some natural area). Forest bathing has been shown to improve both mood and attention capacity.

Maria’s work was on the BBC recently, see video below ↓

Interview by Claire Moran.

Main image from Rowan Hall @RowanHHall, showing Maria on the right with another Grantham Scholar working at the school during the installation of the green barrier.