Meghan Hodges
Trees are a natural remedy for air pollution, which is a pressing issue in many countries. They act as the Earth's purification system, absorbing airborne chemicals and releasing oxygen. Trees remove air pollution through the interception of particulate matter on their surfaces and the absorption of gaseous pollutants through their leaf stomata or 'pores'. The largest of these particles are known as PM10s, which are around a fifth of the width of a human hair, while the smallest are nanoparticle pollutants. Fine particulate matter can easily enter the human respiratory system, causing or exacerbating various diseases. In addition to their natural purification abilities, researchers have created transgenic poplar trees that can break down common environmental pollutants.
| Characteristics | Values |
|---|---|
| Removal of air pollution | 17.4 million tonnes of air pollution removed by trees and forests in the conterminous US in 2010 |
| Health impacts | 850 incidences of human mortality avoided; 670,000 incidences of acute respiratory symptoms avoided |
| Health impacts value | $6.8 billion |
| Removal of pollutants | SO2, NO2, CO, ozone, vinyl chloride, carbon tetrachloride, benzene, chloroform, mercury, lead, cadmium, selenium |
| Reduction of air temperature | Alters concentration of pollutants |
| Reduction of energy consumption | Reduces energy consumption in buildings, reducing consumption of energy from polluting sources |
| Direct removal of pollutants | Through direct uptake of gases or interception of airborne particles |
| Evergreen trees | Act as year-round pollutant filters |
| Coniferous trees | Effective at trapping pollutants due to dense canopy structure |
| Tree pores (stomata) | Absorb toxic pollutants, including SO2, NO2, CO, and ozone |
| Tree surfaces | Temporarily catch particulate matter |
| Tree roots | Take up contaminants through their roots and transport them to leaves and tissues |
| Global emissions absorbed by forests | A third of global emissions |
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What You'll Learn
Trees absorb gaseous molecules and release oxygen
Trees are a natural solution to tackling air pollution. They act as the earth's purification system by absorbing airborne chemicals and releasing oxygen. Trees absorb gaseous molecules in the air through their leaves. The tiny pores on the leaf surfaces, called stomata, take in air that includes toxic pollutants. Once inside the leaf, the gases diffuse into the intercellular spaces and may react with the inner-leaf surfaces. This means pollutants like SO2, NO2, CO, and ozone are permanently converted when inside the leaf.
Trees also absorb carbon dioxide from the atmosphere and use it to build their leaves, branches, trunks, roots, and the soil. They play a critical role in removing air pollutants and greenhouse gases from the atmosphere. In the contiguous United States alone, urban trees remove an estimated 711,000 metric tons of air pollution every year.
The US National Park Service has identified three key impacts of planting trees: altering the concentration of pollutants by reducing air temperatures, reducing energy consumption in buildings, and directly removing pollutants from the air. Trees also help to reduce air pollution by removing some particulate matter from the air by temporarily "catching" it on their vegetative surfaces.
In addition to their natural air-purifying abilities, trees can be genetically modified to break down common environmental pollutants more efficiently. Transgenic poplar trees, for example, can remove trichloroethylene (TCE), a common pollutant at Superfund sites, 45 times more efficiently than non-transgenic cuttings.
By absorbing gaseous molecules and releasing oxygen, trees play a vital role in improving air quality and human health. However, it is important to consider the context when planting trees for pollution reduction, as tree-planting schemes in densely built-up areas may inadvertently trap pollution.
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Trees intercept particulate matter
Trees play a critical role in improving air quality by removing harmful particulate matter from the air we breathe. Particulate matter, especially fine particles known as PM2.5, can easily penetrate the human respiratory system, causing severe health issues. By intercepting these particles, trees help reduce the incidence of bronchitic symptoms, heart attacks, cognitive development problems, and even mortality.
The mechanism by which trees intercept particulate matter involves the use of their vegetative surfaces. Trees "catch" or trap particulate matter on their leaves, stems, and other surfaces, preventing them from remaining suspended in the air. This interception is temporary, as particulates can be washed away by rain or transferred to the soil during precipitation. However, even this temporary interception has significant positive impacts on air quality and human health.
The effectiveness of trees in intercepting particulate matter is influenced by various factors, including wind direction and landscape structure. In certain urban settings, tall trees with large canopies might hinder the dispersal of pollutants, trapping them close to the ground. Therefore, urban planning considerations play a crucial role in maximizing the benefits of trees in intercepting particulate matter.
In addition to their natural abilities, trees have also been genetically modified to enhance their pollutant-intercepting capabilities. Researchers have created transgenic poplar trees that can efficiently break down common environmental pollutants. These trees offer a potential solution for cleaning up contaminated sites more rapidly and cost-effectively than conventional methods.
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Transgenic trees can break down pollutants faster
Trees play a critical role in removing air pollutants and greenhouse gases from the atmosphere. They intercept particulate matter on their surfaces and absorb gaseous pollutants through their leaves. However, the process is often too slow to be practical for environmental cleanup.
To address this issue, researchers have developed transgenic trees that can break down pollutants faster. Transgenic trees are created by adding genes from other organisms, resulting in what are called transgenic plants. For example, researchers have successfully inserted the gene for cytochrome P450, an enzyme that breaks down a wide range of environmental pollutants, into hybrid poplar trees. These transgenic trees processed trichloroethylene (TCE), the most common pollutant at Superfund sites in the United States, 45 times more efficiently than control cuttings without the added gene.
The same research team also found that the transgenic poplars removed 79% of TCE from the air within a week, compared to none for the control cuttings. Additionally, the transgenic trees removed 99% of chloroform, compared to only 18-20% removed by the control cuttings. The transgenic trees were also able to remove other dangerous pollutants such as benzene, carbon tetrachloride, and vinyl chloride more efficiently.
The large size and extensive root systems of these transgenic trees make them ideal for cleaning up contaminated sites faster and at a lower cost than conventional methods. For example, a French hybrid of an aspen tree, a type of poplar, may be able to rid water supplies of TCE, acting as a low-cost solution for cleaning contaminated groundwater. This ability to break down pollutants faster makes transgenic trees a promising tool for environmental remediation and improving air quality.
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Evergreen trees are year-round pollutant filters
Evergreen trees are a powerful tool in the fight against air pollution. Unlike deciduous trees, which lose their leaves in winter, evergreen species retain their foliage year-round, acting as constant filters. Their dense canopy of needle-like leaves is very effective at trapping pollutants, and their seasonal biology helps too.
Evergreens, such as conifers, pines, and cypresses, are particularly good at dispersing and depositing particulate matter (PM). When clouds of minuscule particles crash into the trees, they become dispersed and diluted by the air, reducing the risk of inhalation by humans. The waxy, hairy, or rugged leaves of evergreens then trap the particles, which are washed away by rain.
The effectiveness of evergreen trees as pollutant filters depends on several factors, including canopy size, leaf size, and leaf structure. Bigger canopies and larger leaves can trap more particles, and leaves with rough, rugged, and hairy surfaces act as the "best filters". The acicular needle shape of conifer leaves, for example, makes them more efficient at accumulating PM2.5 (fine particulate matter) than broadleaved species.
In addition to their role in filtering particulate matter, evergreen trees also absorb gaseous pollutants such as SO2, NO2, CO, and ozone through tiny pores on their leaves called stomata. These gases are then broken down within the inner surfaces of the leaves. Furthermore, like all trees, evergreens absorb carbon dioxide from the atmosphere, helping to slow down climate change.
Overall, evergreen trees are valuable year-round pollutant filters that can significantly improve air quality and human health, particularly in urban areas. However, it is important to consider the specific context when planting evergreen trees, as some species can be sensitive to salt levels in soils and their year-round canopy can block sunlight from melting snow and ice, potentially leading to road traffic problems in colder cities.
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Trees reduce energy consumption in buildings
Trees play a critical role in improving air quality by removing air pollutants and greenhouse gases from the atmosphere. In addition to releasing clean oxygen, trees absorb carbon dioxide and use it to build their leaves, branches, trunks, roots, and soil. They also remove some particulate matter from the air by temporarily "catching" it on their surfaces.
The placement of trees is crucial for maximizing their energy-saving benefits. Trees should generally not be planted to the south of a house, as they can block the warming effects of sunlight in the winter. Instead, they can be planted to the north, east, and west of the structure to provide shade in the summer and allow sunlight in the winter. Trees should also be planted at a distance of at least 20 feet from the building to allow for adequate growing space.
The strategic use of trees in urban areas can have a significant impact on energy consumption and costs. Urban trees and forests alter building energy use by providing shade, cooling air temperatures, and altering wind speeds. This leads to reduced electricity and heating use, resulting in substantial energy cost savings for communities.
In summary, trees are a natural and effective way to reduce energy consumption in buildings. By carefully considering the placement and types of trees, individuals and communities can benefit from lower energy costs, improved air quality, and a more comfortable living environment.
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Frequently asked questions
Trees help improve air quality by removing air pollutants and greenhouse gases from the atmosphere. They also release clean oxygen for us to breathe.
Trees absorb airborne pollutants through their leaves, branches, trunks, roots, and the soil. They also intercept particulate matter on their leaves and other surfaces.
According to the US National Park Service, planting trees improves air quality through three key impacts: altering the concentration of pollutants by reducing air temperatures, reducing energy consumption in buildings, and directly removing pollutants from the air.
Urban trees help reduce air pollution and improve air quality, creating a better habitat for wildlife and people. They also provide shade, relieve stress, and promote jobs.
Conifers are effective at reducing particulate matter (PM) due to their dense canopy structure and evergreen nature. Transgenic poplar trees have also been created by researchers to break down common environmental pollutants more efficiently.
