Plants That Purify: Natural Air Filters

Air pollution is a pressing issue, with around 4.2 million premature deaths occurring annually due to its effects. Plants have been proposed as a natural, low-cost solution to this problem, through a process known as phytoremediation. Phytoremediation involves the absorption and degradation of airborne pollutants by plants, which can occur during metabolic activities and through the leaves and roots of plants. While lab studies have demonstrated the effectiveness of plants in absorbing pollutants, there is limited research on the impact of plants in natural, indoor environments. Nonetheless, certain plants are believed to be more effective at improving air quality, including trees and plants with large, leafy surfaces. In addition to their air-purifying capabilities, plants can also provide windbreaks, decrease soil erosion, and trap microbes from the air. However, it is important to consider potential drawbacks, such as the accumulation of dust and pests, which can trigger allergies and asthma symptoms.

The bigger and leafier the plant, the better

Plants have been proven to improve air quality. In a 1989 NASA study, scientists discovered that during photosynthesis, plants "inhale" air pollutants and "exhale" clean oxygen. They purify the air by scrubbing it of toxic volatile organic compounds (VOCs).

While plants are beneficial, it is important to remember that studies on the impact of plants on indoor air pollution have been conducted under strict laboratory conditions. These studies generally involve placing a potted plant in a small, airtight chamber and injecting a singular VOC. However, in the real world, our indoor spaces are larger, and multiple VOCs are present simultaneously. Therefore, it would likely take a significant number of plants to make a substantial difference in mitigating indoor air pollution.

Nevertheless, when it comes to choosing plants to purify the air, bigger and leafier plants are indeed better. Hairy and waxy leaves are even more effective. The size and leafiness of a plant increase its surface area, providing more space for pollutants to be absorbed. Additionally, plants with larger leaves have more space for photosynthesis, allowing them to process more air and absorb more pollutants.

Outdoor trees and plants can also help reduce indoor air pollution. They act as a filter for particulate matter that enters through open windows or on the bottoms of shoes. A study from Lancaster University found that having trees between the road and your front door can reduce indoor particulate matter by half. Again, the bigger the leaf, the better the filtration. Evergreens are a good option for year-round filtration.

It is important to note that some plants may aggravate allergies. Plants with big leaves and no flowers are generally better options. Ferns, weeping figs, yuccas, palms, African violets, orchids, and chrysanthemums may worsen allergies. It is also crucial to keep your plants clean by gently dusting their leaves with a damp cloth weekly to prevent the accumulation and distribution of dust, which can cause respiratory issues.

Houseplants may not clean the air

While plants can improve air quality outdoors, the same may not be true for indoor plants. The commonly held belief that plants clean indoor air can be traced back to a 1989 NASA study that found that plants absorb carbon dioxide and remove volatile organic compounds (VOCs) in a sealed environment. However, our indoor environments are not sealed like a space station, and the sample sizes used in the NASA study were very small, so their findings don't necessarily translate to real-world settings.

Additionally, studies on the impact of plants in natural indoor environments are limited and have faced challenges such as inaccurate measuring equipment and failure to control or measure the air exchange rate. It is difficult to determine if the nominal reductions in VOC concentrations observed in some studies can be attributed to the plants or air exchange. While plants may help reduce air pollution in laboratories, it would likely take a significant number of plants to have a noticeable impact in a real-life setting.

Furthermore, houseplants can have some drawbacks when it comes to air quality. Dust can accumulate on leaves and distribute into the air, causing respiratory issues and worsening allergies, asthma, and COPD symptoms. Pests such as aphids, spider mites, and mealybugs can also be introduced, and there is a potential for mould growth on the soil if plants are overwatered. Certain plants, including ferns, weeping figs, and palms, may even aggravate allergies.

Instead of relying solely on houseplants, there are more effective ways to reduce indoor air pollution. The best approach is to prevent pollutants from entering the air in the first place by eliminating or reducing the use of products that contain high levels of VOCs, such as cleaning products, air fresheners, and paints. Increasing ventilation by opening doors and windows or using mechanical ventilation, such as fans or HVAC systems, is also crucial in diluting indoor air pollution.

While houseplants may not be the solution for cleaning the air, they can still offer other benefits. Indoor plants have been shown to lower blood pressure, reduce stress, and lessen cold symptoms. They can also improve mental health and increase the number of beneficial microbes in the home. However, when it comes to air purification, it is best to combine plants with proven methods, such as source control and ventilation.

Outdoor plants reduce indoor air pollution

Plants are not only aesthetically pleasing, but they also have the potential to improve your indoor air quality and clean the air in and around your home. Outdoor plants can reduce indoor air pollution by filtering out particulate matter that may enter your home through open windows or on the bottoms of your shoes.

Mechanisms of Phytoremediation

The process by which plants reduce air pollution is called phytoremediation. This is an environmental remediation technology that uses plants to absorb and degrade airborne pollutants through metabolic activities. The absorption of pollutants occurs mainly on the surface of plants, particularly on the stomata of leaves, and is influenced by factors such as pore characteristics and planting patterns. The degradation of pollutants involves the decomposition of foreign substances by plant metabolites such as enzymes.

Effectiveness of Outdoor Plants

Studies have shown that having trees between the road and your home can reduce indoor particulate matter by up to half. Additionally, restoring a native tree canopy can reduce air pollution by 27%. The bigger the leaf, the better the plant is at filtering the air. Evergreens may be preferable for year-round filtration, depending on your location.

Considerations

While outdoor plants can help reduce indoor air pollution, it is important to note that they are more effective in conjunction with other measures. Indoor plants, for example, can also improve air quality, but they may trigger allergies or asthma symptoms if not properly maintained. Dust can accumulate on leaves and distribute into the air, and overwatering can lead to mould growth. It is also important to choose the right types of plants, as certain plants may exacerbate allergies.

Overall, incorporating a diverse range of native outdoor plants, including trees, can help reduce indoor air pollution and improve the air quality in your home and the surrounding environment.

Urban forests can scrub the air

Urban forests can play a crucial role in improving air quality and scrubbing the air of harmful pollutants. Trees in urban forests contribute to better air quality through several mechanisms. Firstly, they directly remove pollutants from the air, including ozone, gaseous air pollution, and particulate matter. Trees act as natural filters, trapping airborne particles on their leaves and stems, preventing them from entering our homes and lungs. This interception of particles contributes to healthier air for city dwellers.

Additionally, urban forests help reduce air temperature, which has an indirect effect on pollution concentrations. Lower temperatures can lead to reduced energy consumption in buildings, resulting in decreased air pollutant emissions from power sources. This dual effect of urban forests on temperature and emissions plays a significant role in improving air quality.

The benefits of urban forests go beyond air quality. They also provide shade, habitat for wildlife, and can help mitigate the urban heat island effect, reducing the need for energy-intensive cooling. Furthermore, trees absorb carbon dioxide and release oxygen through photosynthesis, contributing to the mitigation of greenhouse gases and global climate change.

While the positive impact of urban forests is clear, they are vulnerable to various threats. Climate change, extreme weather events, droughts, and new diseases pose significant risks to the health and survival of urban trees. Proper maintenance, diverse species selection, and conservation strategies are crucial for ensuring the resilience of urban forests in the face of these challenges.

In conclusion, urban forests are a powerful tool in the fight against air pollution. They scrub the air of harmful pollutants, reduce temperatures, and contribute to a healthier, more sustainable urban environment. By investing in and protecting our urban forests, we can reap the benefits of cleaner air and improved quality of life for years to come.

Native plants encourage biodiversity

Plants are natural air purifiers. They improve air quality by absorbing carbon dioxide and releasing oxygen during photosynthesis, simultaneously absorbing air pollutants and toxic VOCs.

Native plants are those that occur naturally in a specific region and have evolved over thousands of years. They are fundamental to maintaining ecological balance and supporting biodiversity. By choosing native plants for your garden or landscape, you can contribute to biodiversity conservation and support the ecosystem that depends on these indigenous species.

Native plants provide habitat and food sources for native wildlife, including insects and birds. Insects, for example, consume plant material and turn it into protein that larger animals need. Native oak trees, for instance, support over 500 species of caterpillars, which are an important food source for birds. Native plants also help combat climate change by storing carbon dioxide and reducing the need for chemical pesticides and synthetic fertilizers, which can be harmful to the environment.

In addition to their ecological benefits, native plants often require less maintenance and water than non-native species as they are adapted to local environmental conditions. They can also provide aesthetic value with their beautiful flowers, fruits, and seasonal colour changes.

To effectively incorporate native plants, research which varieties are native to your area and understand their specific needs and ecological roles. This way, you can enhance the biodiversity and resilience of your local ecosystem while creating a beautiful and sustainable landscape.

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