Urban trees can increase ozone pollution during heatwaves, study finds

A study led by researchers from Jinan University and the University of Innsbruck has found that certain tree species in urban environments can worsen ground-level ozone pollution during heatwaves. While urban greenery provides essential cooling and absorbs some pollutants, some trees emit biogenic volatile organic compounds (BVOCs), such as isoprene, which react with nitrogen oxides in sunlight to form ozone.

Research conducted in Beijing using a monitoring system on a 102-meter meteorological tower revealed that while biogenic sources accounted for only about one-tenth of measured volatile organic compound (VOC) emissions, they contributed nearly half of the total VOC reactivity. The study noted that as temperatures rise between 20°C and 35°C, the chemical reactivity of these emissions can increase seven to eightfold.

The findings suggest that urban planning should focus on smarter greening strategies, emphasizing the selection of specific tree species and the control of nitrogen oxides to mitigate the unintended atmospheric consequences of urban forests.