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Plants Cause Air Pollution During Heat Waves

Plants are air-polluting when it’s super hot! Or so says a new study published in the journal Environmental Science & Technology.


Plants are an important source of air pollution during heat waves because they emit chemicals that can react to form ozone. But,we know only good of plants (mostly), right?! During the day, they take in carbon dioxide from our environment, and breathe out oxygen which we need, thus purifying the air. Furthermore, the negative impacts of deforestation have been revealed decades ago, and more and more research is highlighting the importance of having plants around us. However, the new study suggests that plants can also be the bad guys under certain conditions.

Heat waves apparently turn plants into monsters. While planting trees does make environments cleaner and greener, with healthier air, city trees have the potential of boosting air pollution levels. Drastic increases in temperature have been linked with a rise in ozone: up to 60% of ground-level ozone is formed by reactions between chemicals present in the environment, and those released by urban shrubs and other plants.

Compounds produced by plants, like, isoprene, monoterpenes, and sesquiterpenes can react with man-made substances like nitrogen oxides (coming from vehicles) to produce ground-level ozone. The resulting small particles, comparable to soot, accumulate in the air, thereby polluting it.

Led by Galina Churkina from Berlin’s Humboldt University, the team looked into simulations entailing chemicals released from plants found in the Berlin-Brandenburg metropolitan area. They used data obtained from two summers, one in 2006, when a heat wave was experienced, and the other in 2014, when the temperature remained within the normal range. The simulations show that under normal summer temperatures (an average of 25° Celsius), plants would emit chemicals that would account for 6 to 20% of ozone formation. However, plant emissions reached new peaks during heatwaves (when temperatures go beyond 30°C), resulting in ozone formation up to 60%. Churkina deems the magnitude of this interaction “quite amazing”.

Is this even real, you might be wondering. Should we, now, cut down trees in urban areas? No, the study should not be interpreted as such, according to urban planning expert, Robert Young from the University of Texas, who was not part of the new research. He explains that we should not stop planting trees, but that measures curbing air pollution from other sources should be made more strict. As for trees polluting the air, Young explains that “everything has multiple effects”.

To conclude, study author Churkina explains that including trees in urban spaces is not enough. Such campaigns should not be implemented in isolation; rather, they will only be beneficial if they are combined with the reduction of other air pollutants (for instance, those coming from vehicles) together with the use of green energy sources.


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