Trees in cities provide shade, reduce surface temperatures by releasing moisture, absorb carbon from the air, clean the air of soot and other pollutants, provide habitat for wildlife, and are simply a feast for the eyes.
However, planting certain types of trees can actually worsen the air quality. This was shown by a study of the situation in New York conducted by scientists from the Columbia Climate School (USA), the university’s press service reports.
It is noted that oak and ash trees, which now make up the majority of trees in New York, produce huge amounts of volatile compounds called isoprenes.
The leaves of some tree species emit isoprene as a byproduct of photosynthesis, although no one knows exactly why. In the case of oak trees, their emissions tend to increase exponentially with heat, at least until air temperatures reach over 30 degrees.
Some scientists believe this helps keep leaf tissue from drooping and losing its ability to photosynthesize when it gets hotter. Emissions of these and other volatile compounds from trees may be linked to the attraction of pollinating insects.
For some reason, oaks and ash trees are particularly prolific – oaks emit 800 times more isoprene than maples or London sycamores.
Harmless in itself, isoprene quickly reacts with nitrogen oxide pollutants emitted by vehicles, buildings and industry to form ground-level ozone, a major factor in many respiratory diseases, especially chronic bronchitis and asthma, the article says.
Scientists combined data from satellite images and tree species censuses conducted by the local Parks Department to model how trees interact with emissions from cars and industry.
They found that in New York City, isoprene emissions from trees play a significant role in ozone formation on hot summer days, when levels routinely exceed the safe limit of 70 parts per billion, sometimes reaching 100 parts per billion. Planting more trees could finally push that level even higher, according to the study.
But isoprene emitted from trees alone is not the culprit—ozone cannot form without one important precursor chemical: nitrogen oxides, also known as NOx, emitted when fossil fuels are burned by vehicles, hot water boilers, power plants, and industry.
If we significantly reduced NOx emissions, trees would not be a problem, the scientists emphasize. We do not want to convey the idea that trees pollute the air. It is cars.
Trees can make drought more intense.
Source: Racurs
I am David Wyatt, a professional writer and journalist for Buna Times. I specialize in the world section of news coverage, where I bring to light stories and issues that affect us globally. As a graduate of Journalism, I have always had the passion to spread knowledge through writing.