The predominance of certain trees in a street can raise the concentration of ozone in the air. The presence of ozone at ground level can lead to various diseases in humans such as asthma, bronchitis, and other breathing problems.Trees emit volatile organic compounds (VOC), these substances under the presence of solar radiation react with nitogen oxides given out by the smoke of the traffic to form ozone.
Chimneys and cars emit VOC as a byproduct of the burning of fossil fuels; trees emit VOC, for other reasons, to repel harmful insects and to attract pollinators. Poplars, oaks, willows and tupelo are species which emit the greatest amounts of VOC into the atmosphere.
Barcelona showing the tree-lined (London Plane) Ramblas.
Are these trees causing more harm than good in an already polluted city?
But people don't have to worry as for this to happen, many conditions have to be present at once: sun and a warm atmosphere. Cold and cloudy cities have less reasons to worry. But climate change and global warming could all of this to change.
So, does this mean that we have to cut down all of the trees that emit large amounts of VOC? No, if the city is well arranged and the trees are regularly spaced out there is no problem of having them in a city, but organisations that plan to plant trees as a way to decrease the levels of CO2 should be really careful when choosing the species to plant as they could harm their environment without even knowing it.
Of course there is another way to prevent this. If we could decrease the emissions of traffic VOC we wouldn't need to be worries about the trees as they will have nothing to react with.
This was written by Pablo Raventós Surroca
3rd ESO Combined Science