There is no cure for every disease. Nor those whom the Earth suffers. Even trees don’t always work as a miraculous therapy against urban air pollution. Actually, Under certain conditions some Trees can have a detrimental effect on air quality.
This is the result of research carried out by Donato Kofel, a graduate of Environmental Science and Engineering from the Federal Polytechnic School of Lausanne (EPFL), for his master’s project. Kofel set the figure Positive and negative effects of trees on air quality Exterior in the Swiss canton of Geneva.
To do this, he explored the world of geographic information systems (GIS), a type of advanced mapping software. “These maps convey so much information in a single image that it allows people to capture it all at once,” he says.
Researcher develops new way to use GIS application to study How trees affect air quality From the canton of Geneva. Kofel relied on an inventory of around 240,000 ‘isolated’ trees; that is, it is located outside the forested areas.
For example, trees lined up along a boulevard or planted in a city park. Isolated trees in the Geneva inventory represent about 25% of the canton’s total. The inventory lists various tree characteristics such as species, location, trunk height, trunk diameter, and crown diameter.
The analyst used this data to create maps of the total leaf area of the trees, which gave an indication of them. the ability to filter particles in the air. In parallel, he examined another important process: The role of trees in the formation and accumulation of ozone.
Oaks under the spotlight
The positive aspects of trees are well known; among others, help lower the temperature in urban areas, filter fine particles the atmosphere, CO2 capture And release oxygen.
But it also has some downsides. For example, naturally emits biogenic volatile organic compounds (BVOC) at varying rates depending on factors such as tree species, air temperature and humidity, amount of sunlight, whether trees are damaged or under stress.
Oak trees emit compounds that turn into ozone that can be harmful to humans
These BVOCs are then they turn into ozone by photochemical oxidation with other compounds released into the air as a result of human activities. Ozone negatively affects health and the environment.
The environmental engineer calculated the ozone generation potential of emissions from trees and was surprised to find that: Under certain conditions, trees can also have detrimental effects on air quality..
Their initial task was to collect literature on the 51 most common tree species in the canton of Geneva and use this information to calculate hourly BVOC emission rates.
During the analysis, it was found that: Some oak species have the highest BVOC emission rates and thus the greatest potential for ozone formation.. Oak is the most common tree in the streets and parks of the canton of Geneva.
With the help of two other scientists, Romana Paganini and Ilann Bourgeois, she estimated how much particulate matter and ozone urban trees are filtered out each year to highlight their positive effects. Detailed maps show:Urban trees removed about 25% of the particles produced by anthropogenic activity in the canton of Geneva.
additional air pollution
But the research also revealed that the ozone-forming potential of these trees is about 10 times the destroying potential. It emits 130 metric tons of BVOC per yearThis is equivalent to about 18% of VOCs emitted by road traffic each year.
The results show that anthropogenic activities emit enough nitrogen oxides for proper chemical reactions to occur to form ozone.
“Humans have the potential to reduce ozone formation from trees by reducing their nitrogen oxide emissions.EPFL communicator Sandrine Perroud explains: “It depends on the actual mixture of BVOC and these oxides.”
Translation: No clear answer as to how good the trees in the city are in terms of air quality Because Its combination with anthropogenic emissions can lead to additional air pollution under certain conditions.
Kofel points out that more in-depth studies are needed to clarify all the questions. But for now, their findings show that trees can make a significant contribution to improving urban air quality. they are not a miraculous cure in all circumstances.
“The air pollution problem needs to be addressed at the source, taking into account both road traffic and other emission sources,” adds Kofel. In any case, city planners can use this environmental engineer’s method to design their own projects. large-scale planting programs are more effective.
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