Scientist indicates that three types of trees have the capacity to improve air quality in winter by retaining ultrafine and nano-size particles.
The laurel-in-bloom (Nerium oleander), the Australian laurel (Pittosporum tobira) and broad-leaf privet (Ligustrum lucidum) keep their leaves throughout the year, contributing to reduce atmospheric contamination in the most critical winter months.
Dr. Sergio Castro, a member of the Center for the Development of Nanoscience and Nanotechnology (Cedenna), has been investigating the impact of trees on urban environments. He has studied the behavior of three ornamental species that are widely distributed in the city of Santiago and whose characteristics could help reduce the quantity of atmospheric particles throughout the year.
Unlike most trees in the city, these species retain their leaves in winter, which allows them to capture small particles in the air caused by hydrocarbon pollution and other contaminants during the most critical season of the year.
The World Health Organization currently recommends suggests parameters to assess air quality based concentrations of particles with diameters between 10 and 2.5 microns. However, there are even smaller particles that, although known at the level of environmental studies, are not regulated by the Chilean law. These particles of ultrafine material or nanoparticles, are identified as MP 0.1 (because they measure close to 100 nanometers or 0.1 micron), because it is an ultrafine fraction of airborne dust, also derived from the combustion of hydrocarbons. To observe these nanostructures, it is necessary to use electronic microscopy equipment, since their dimensions are equivalent to millionths of a millimeter.
“This material has even more important impact on human health than larger particles, given that they are absorbed directly through the alveoli, and long-term exposure to them can result in chronic respiratory disease and ultimately lead to cancer.”, explained Dr. Castro, who is also a professor of the Faculty of Chemistry and Biology of the University of Santiago.
Several studies have shown that tree species that retain atmospheric particles in their leaves can mitigate pollution. However, most trees in Santiago lose their leaves in winter (deciduous species). “If the vegetation increases in Santiago, selecting species that are more efficient in retaining atmospheric particles, we could increase the mitigating effect by 10 to 20%, which is not a negligible result when we consider the public policies to improve urban air quality”, stated Dr. Castro.
The tree species that have been currently been studied are the laurel en flor (Nerium oleander), the Australian laurel (Pittosporum tobira) and the broad-leaf privet (Ligustrum lucidum). Part of this study has been published in the journal Water, Air and Soil Pollution.
City and Planning and Risk in the context of water shortage
In the second half of the 19th century Benjamín Vicuña Mackenna set out to change the face of Santiago, imitating European trends in architecture and ornamentation. An extensive and unprecedented program of urban beautification began, with the introduction of exotic plants to beautify the first parks. The species of native trees of the country were not considered in this project. This initiative has deeply ingrained our way of adorning the city, in particular in terms of the plant species to be used. At present, only 15% of the tree species in Santiago are native to the region, while the majority are foreign species. Some European and North American cities contrast sharply with Santiago, since most of their urban flora remains native.
The predominance of imported species in Santiago reveals another conflict that until now has not been explored. The projections of climate change in Chile indicate that water availability will be critically reduced. Given that foreign species from regions with climates different from our own require more water (because of which they watered), the ornamental flora of the city will have an impact on efforts to economize with available water.
This situation makes it necessary to begin replacing ornamental species, which makes and would be more sustainable. Ideally, we should move toward using native plants as ornamental elements in Santiago, favoring their conservation and contributing to a more economic use of water”, he concluded.