Cities usually take away green spaces. Since prehistoric times, humans have been busily clearing forests to make way for settlements. On an increasing basis, however, greenery has been making a comeback in urban spaces and with good reason. The fact is that vegetation helps cities become better habitats for people and wildlife. Vegetation also helps make the city air safer.
Trees have a remarkable range of traits that can help reduce air pollution. Cities around the world are looking to harness them. Paris, London and Beijing are all trying to use trees to reduce air pollution. Of course, other cities are engaging in this activity as well.
Now, while trees are generally effective at reducing air pollution in an urban landscape, it does not mean that the more trees you have the better the air quality will be. Some trees are more effective at filtering pollutants from the air than others. To make the most difference in air quality in a street or city, it has to be the right tree for the job.
So, how do we pick the right tree for the job? What sorts of factors make a tree better at improving air quality than others? What types of trees do just that?
Well, before we get into that, let’s discuss how trees improve air quality in direct and indirect ways. Indirectly, trees can shade surfaces and reduce temperatures. If a building is shaded by trees, it can reduce the need for conventional air conditioning and the emissions of greenhouse gases that come with it. Lower temperatures also decrease the risk of harmful pollutants like ground level ozone that commonly spikes on hot days in urban areas.
Trees also have a direct role in removing pollutants from the air. Plants are often thought of as the ‘lungs’ of an ecosystem because they absorb carbon dioxide and emit oxygen. However, they also act as the ecosystem’s ‘liver’ too. Why? They remove toxins, or pollutants, like sulphur dioxide and nitrogen dioxide from the area.
How do trees help people in urban landscapes? Trees are particularly effective at removing particle matter (PM). PM comes in the form of tiny particles or organic chemicals, acids, metals, and dust, emitted from fossil-fuel-burning vehicles and factories as well as construction sites. Fine particulate matter can easily penetrate into human respiratory system causing lung and cardiovascular diseases or exacerbating respiratory illness. It has also been linked to inflammation and heart disease.
Trees and plants act as a readily available set of PM purifiers. They do this in two ways. The first is dispersion by crashing into trees and plants. The concentrated clouds of miniscule particles get dispersed and so diluted by the air that it decreases the risk of the inhalation by humans. The second one is deposition. PM can get easily trapped in the waxy, hairy leaves of trees and shrubs. When it rains, most of these particles are washed away by water into drains.
Canopy size, leaf size and leaf structure help determine how effective a tree is at reducing PM. Bigger canopies trap more particles than smaller canopies and larger leaves trap more pollutants than small ones. The leaf type that is most beneficial are those with rough, rugged and hairy surfaces. Silver birch, yew and elder trees were the most effective at capturing particles. Conifers, like pines and cypresses, are also good natural air purifiers.
Of course, there are more factors than these that determine whether a tree is beneficial in removing air pollution from urban landscapes. We hope we’ve given you some interesting and important information. We strive to bring you the best tree news each and every week. Keep coming back to check out our blog for the most up-to-date articles and information.
