Posted by Client Relations on Mon, Jun 15, 2020 @ 5:01 AM
The Best Tree Species for Reducing Air Pollution
Are you looking for an effective way to reduce air pollution? Trees play a crucial role in reducing air pollution by absorbing and capturing carbon dioxide and other harmful gases and particulate matter from the air, releasing oxygen back into the atmosphere, and filtering out particulate matter and pollutants. In this article, we’ll discuss how to reduce air pollution with trees, including the impact of different pollutants on trees, how to involve communities in tree planting and conservation efforts, and how government policies can impact tree planting and conservation efforts.
It’s well established that urban trees reduce air pollution, along with a raft of other benefits. But when it comes to cutting pollution, all trees are not created equal. So, which species do the best job?
Recent research suggests that tiny hairs on plant leaves play a big role in trapping the solid and liquid particles that make up PM (particulate matter) which is responsible, by one estimate, for 8.9 deaths a year globally.
In one recent study, Barbara Maher and colleagues at the University of Lancaster tested the ability of nine tree species to capture PM in wind-tunnel experiments. Silver birch, yew and elder trees were the most effective at capturing particles, with the hairs of their leaves contributing to reduction rates of 79%, 71% and 70% respectively. In contrast, nettles emerged as the least useful of the species studied, though they still captured a respectable 32%. Conifers, like pines and cypresses, are also good natural purifiers.
Ultimately though, it is context that determines if a species is beneficial or detrimental. “Even ‘best-performing trees’ may not work in some cases,” says Prashant Kumar, Founding Director of the Global Centre for Clean Air Research at the University of Surrey. “For example, we would not recommend planting yew near school playgrounds because it is poisonous.”
Stephanie Carlisle, an urban ecologist at the University of Pennsylvania, agrees, saying “Some designers have a tendency to think in terms of objects rather than a complex ecological system. But without a holistic understanding of urban ecosystems, the risk is to do more harm than good.”
In that sense, tree planting to tackle pollution is like many other aspects of urban design – the key to success lies in understanding local and environmental nuances. This is what determines whether urban trees are a breath of fresh air or a major headache.
How to Reduce Air Pollution with Trees
- Trees absorb carbon dioxide and release oxygen back into the atmosphere, as well as filter out particulate matter and pollutants from the air.
- Different tree species are better suited to certain climates and environments, and it is important to choose the right species for maximum benefits.
- Planting and maintaining trees, as well as incorporating them in urban areas, can significantly reduce air pollution.
How Trees Help Reduce Air Pollution
| Tree Species | Pollutants Absorbed | Other Benefits |
|---|---|---|
| English Oak | Nitrogen dioxide, Sulphur dioxide, Particulate matter | Provides habitat for wildlife |
| Eastern White Pine | Ozone, Nitrogen dioxide, Sulphur dioxide, Particulate matter | Reduces noise pollution |
| Red Maple | Ozone, Nitrogen dioxide, Particulate matter | Tolerates urban environments |
| Honey Locust | Particulate matter, Carbon monoxide | Provides shade and reduces energy consumption |
| Green Ash | Ozone, Particulate matter | Tolerates a wide range of soil types |
Trees are effective in reducing air pollution by absorbing carbon dioxide and other harmful gases from the air, releasing oxygen back into the atmosphere, and filtering out particulate matter and pollutants from the air. Trees absorb pollutants through their leaves and tree roots. The process of photosynthesis helps to break down pollutants and convert them into harmless compounds. Stomata, which are tiny pores and hairs on the leaves of trees, play an important role in the exchange of gases between the tree and the atmosphere. Additionally, trees can absorb other pollutants like sulfur dioxide, nitrogen dioxide, and particulate matter through their leaves.
Non-deciduous trees or evergreen trees are ideal for planting in dense urban environments such as industrial estates as the trees are leafy all year round to provide constant air pollution reduction.
How Trees Purify Air?
So, how how do trees clean the air? A trees role in purifying the air through a process known as phytoremediation, where trees and plants, help mitigate pollution by absorbing and neutralizing pollutants from the air. Here’s how trees contribute to air purification to clean the air of urban spaces:
- Absorption of Pollutants: Trees have the ability to absorb various airborne pollutants, including carbon dioxide (CO2), ozone (O3), sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter. Through tiny openings called stomata on their leaves, trees intake these pollutants during photosynthesis, where they absorb carbon dioxide and release oxygen.
- Filtering Particulate Matter: Trees act as natural filters by trapping airborne particles like dust, smoke, and other particulate matter on their leaves and bark. As air passes through the tree canopy, these particles are captured and retained, effectively reducing their presence in the surrounding air.
- Chemical Transformation: Once pollutants are absorbed by the tree, they undergo various chemical processes within the plant. Some pollutants are broken down or transformed into less harmful compounds through biochemical reactions occurring within the leaves and stem.
- Oxygen Release: During photosynthesis, trees convert absorbed carbon dioxide into oxygen, releasing it back into the atmosphere. This oxygenation process is essential for enhancing air quality and supporting life.
- Microbial Action in Soil: Trees contribute to air purification indirectly through their root systems. The root zone and surrounding soil host microorganisms that can break down pollutants absorbed by the roots, effectively cleansing the soil and groundwater from certain contaminants, which indirectly benefits air quality.
How much CO2 Can A Tree Absorb?
The amount of carbon dioxide (CO2) that a tree can absorb varies based on several factors, including the tree species, age, size, environmental conditions, and geographical location. On average, a mature tree can absorb anywhere from 48 pounds (22 kilograms) to several hundred pounds (over 100 kilograms) of carbon dioxide annually.
Researchers have found that Street trees and their soil absorb more CO2 when compared to their forest counterparts.
The Impact of Different Pollutants on Trees
While trees can absorb a wide range of pollutants, different pollutants can have varying impacts on trees. For example, high levels of ozone in the air can damage the leaves of trees, urban and street trees absorb up to 9x the pollutants their forest counterparts do so when picking a tree it’s important to choose the right tree species for your environment and ensure that they are properly maintained to maximize their ability to absorb pollutants. Remember a city or urban setting is also a type of environment so choosing a tree that has shown to grow in those types of hard environments are an important consideration when looking at ways of reducing air pollution
Measuring the Impact of Trees on Air Quality
Air quality and soil monitoring can be used to measure the impact of trees. By monitoring air quality and soil before and after tree planting initiatives, it’s possible to determine the effectiveness of these efforts in reducing pollution. It’s important to note that the impact of trees on air quality can vary depending on factors such as the number and species of trees planted, the location of the trees, and the level of air pollution in the area.
Watch our video from our 2023 event ‘Where the Shade Hits the Pavement‘ where GP Dr. Kim Loo explain how trees improve the physical and mental health outcomes of her patients in western Sydney.
Involving Communities in Tree Planting and Conservation Efforts
Community involvement is essential for successful tree planting and conservation efforts. Community members can participate in tree planting initiatives and help maintain trees in their neighborhoods. Education and outreach programs can be used to raise awareness of the benefits of trees and encourage community involvement in tree planting and conservation efforts.
The Impact of Government Policies on Tree Planting and Conservation Efforts
Government policies can have a significant impact on tree planting and conservation efforts. Government initiatives and programs can provide funding and support for tree planting and conservation efforts. Examples of successful initiatives include New York City’s MillionTreesNYC program and the US Forest Service’s Urban and Community Forestry program. Advocating for greater investment in tree planting and conservation efforts can help ensure that these efforts are successful.
Case Study: Choosing the Right Tree Species for Maximum Benefits
In February 2011, two different tree pits were planted at the same time with the same tree species (Chinese Elm) at the Ashfield Civic Centre in Sydney, Australia. The tree in the centre forecourt was planted using the Stratacell™ suspended pavement system while the two trees near the sidewalk were planted in structural soil (rock/soil matrix).
Over 9 year later, the canopy density of the tree planted using the Stratacell system (suspended pavement – right) is significantly thicker than the one on structural soil (rock/soil – shown on left). This highlights how trees planted in less then ideal growing conditions suffer long term and don’t end up providing the full value.
See the full case study results here.
Additional Ways Trees Reduce Air Pollution
While planting trees is an effective way of reducing air pollution, there are other steps individuals can take to reduce their impact on the environment. These include reducing energy consumption, supporting clean energy initiatives, using alternative transportation methods, and reducing waste.
Conclusion
Reducing air pollution is crucial for protecting human health and the environment. Planting trees is an effective way to reduce air pollution by absorbing carbon dioxide and other harmful gases, releasing oxygen back into the atmosphere, and filtering out particulate matter and pollutants. By involving communities and advocating for government policies that support tree planting and conservation efforts, we can create a sustainable future for all.
Questions and Answers
Who can plant trees to reduce air pollution?
Anyone can plant trees, from individuals to organizations. It’s best to reach out to your local council or government department and they can inform your of the correct trees to plant for your area.
What types of trees are best for reducing air pollution?
Trees that are native to your area and have large canopies. Silver birch, yew and elder trees were the most effective at capturing particles,
How do trees reduce air pollution?
Trees absorb harmful pollutants through their leaves, roots and soil.
How long does it take for trees to reduce air pollution?
Trees can begin to reduce air pollution immediately, but it takes years to see significant improvements. Larger tree canopies provide the best results in reducing the urban heat island effect so it best to ensure the trees are able to grow as fast as possible so their environmental benefits can be enjoyed sooner.
What if I live in an urban area with little greenery?
You can support efforts to increase green spaces and plant trees in your community. Soil vault systems such as Citygreens Stratavault are the best solution for providing trees with sufficent soil in urban areas.