Alia Fawaz

Driving along highways that are lined with trees is always a pleasant experience. Miles of leafy roads add beauty and much shade to the pleasure of driving. However, aesthetics alone was not the motive for Indian leaders when they recently announced their plans to plant a record number of trees on their country’s highways.

Reducing unemployment and air pollution were the two main reasons for India’s ambitious project. The Ministry of Rural Development has announced that it will hire 300,000 youths to plant two billion trees along India’s 62,137 miles of highway. India, the country with the world‘s second largest population, is actually home to six of the World Health Organization’s 10 cities with the worst air pollution. Deforestation continues to be a major challenge as well. Clearly, the extra foliage will make a significant difference towards producing cleaner air.

Trees capture particulate matter

In fact, a recent U.K.-led study has proven that tree leaves can capture a substantial amount of particulate pollution–the air pollutants that most commonly affect people’s health. Scientists in this study performed an experiment to measure how much air pollution ends up in a certain number of homes in the same neighbourhood by using dust-monitoring devices; first by swiping surfaces and then analyzing what was collected by means of magnetic remanence (residual magnetism), a technique that provides information on concentrations of iron bearing particles.

The scientists then placed a screen of 30 young silver birch trees in wooden planters in front of several of the houses for 13 days, while the same number of houses did not have the planters. Wipes from all the houses showed that the ones with the tree screens in front of them had between 52 percent and 65 percent less concentration of metallic particles. The houses with the trees in front of them also showed a 50 percent reduction in PM1, PM2.5 and PM10 (PM1= particulate matter with a diameter of one micrometer or less; PM 2.5 = particulate matter with a diameter of 2.5 micrometers or less; and PM 10 = particulate matter with a diameter of 10 micrometers or less).

The researchers examined the silver birch leaves with a scanning electron microscope. They confirmed that the hairy surfaces of the leaves trapped the toxic metallic particles. These particles came primarily from combustion and brake wear from passing vehicles.