Plants becoming a source of air pollution?

Plants becoming a source of air pollution?

For the most part planting trees are seen as a “green” and “pro-environment” choice but recently researchers discovered that trees planted in cities could be boosting pollution levels. During heat waves, city trees and urban shrubbery release chemicals that contribute to as much as 60 percent of ground-level ozone, according to a report in Environmental Science and Technology.

However this does not mean that planting trees and plants in cities should stop but more severe measures are needed to control other sources of pollution such as vehicle emissions and factory emissions. 

There are many benefits to city trees including providing cooling shade, reducing stormwater runoff, and most importantly converting carbon dioxide to oxygen. Research also shows, however, that trees and other shrubs release chemicals called volatile organic compounds (VOC’s), which in the presence of sunlight react with nitrogen oxides in vehicle fumes to form ozone, one of the components in smog that makes it a health threat; they interact with their surrounding environment producing polluted air. VOC’s are emitted out of tailpipes and smokestacks as a byproduct of burning fossil fuels but trees emit them in part to repel insects and to attract pollinators. Isoprene, for example, can react with human-made compounds, such as nitrogen oxides, to form ground level ozone which is a colorless gas that can be hazardous to human health at certain quantities. Other chemicals called, monoterpenes and sesquiterpenes also react to nitrogen oxides and when they do many tiny particles build up in the air. Cars and trucks are the major sources of these oxides in cities.

In the study, researchers found that at normal maximum summer temperature, around 35 Celsius, plants’ chemical emissions contributed to about 6 to 60 percent of ozone formation in the simulations. However, at peak temperatures during the heat wave, temperatures over 30 Celsius plant emissions spiked, boosting their share of ozone production to 60 percent.

As a result researchers are advising that if trees are to be added to urban spaced they
can’t be done in isolation. Adding trees will improve quality of life only if they are combined with a radical reduction of other sources of pollution from motorized vehicles, and in increase in the use of clean energy sources.