Everyone knows that trees help clean the air by converting carbon dioxide into oxygen – but it appears that they are able to do more than that. A recent study has shown that silver birch trees can absorb as much as 50% of the particulate matter generated by automobiles. This comes from lead author Barbara Maher from the University of Lancaster and has been published in the journal Environmental Science & Technology.
Automobiles generate a lot of particulate matter (PM) in the form of exhaust, brake pad dust, and general metallic road dust. These particles, which can be solid or liquid, are kicked up into the air. This PM has already been linked to respiratory problems like asthma and lung disease, and those who live in urban settings are at an increased risk for these diseases due to heavier and more frequent exposure. Because the bits are so small, they are easily inhaled and become embedded in respiratory tissue.
The study sought to understand how trees control pollution, so that landscapers can get the most out of both form and function of the trees. The researchers used silver birch trees, which are found throughout Europe and in southwest Asia. It is important to note that not all trees have the same ability to collect PM.
The study was carried out on one city block and PM content was determined based on dust samples taken from each of the eight homes participating in the experiment. This was done to determine how much PM was being inhaled by the families on the street. After initial samples were taken, the streets were then lined with silver birch trees in front of four of the homes, effectively creating a barrier between the home and the streets full of cars. A moist towelette was used to collect dust samples from the television screen, while a PM detector scanned the air every ten minutes. At the end of the nearly two-week-long trial, the research team noticed that the houses with a birch tree screen had over a 50% decrease in metallic PM compared to the homes that did not.
The team then needed to find out how the trees were able to filter out PM so efficiently. After examining leaves with a scanning electron microscope, they discovered that tiny hair-like structures were responsible for removing the particulates from the air.
Large amounts of further study are needed to see how readily the leaves filter the PM, if it has any adverse affect on the trees, and if the PM will actually stay trapped on the leaves or if it will shake out heavy PM to be blown on houses downwind.
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