Published : 28 Aug 2026, 04:56 AM
Updated : 08 Sep 2026, 09:36 AM
Some trees planted in cities release potentially toxic chemical vapours that contribute to ground-level ozone pollution -- and rising temperatures are making the problem worse, according to a new study that could reshape how urban green spaces are designed.
Researchers from Jinan University in China set up an emissions monitoring system on a 102-metre platform atop Beijing's meteorological tower, tracking chemical signals in the atmosphere several times per second, reports The Independent.
The setup allowed scientists to capture the city's chemical composition in real time and trace volatile organic compounds (VOCs) back to their sources -- including trees, traffic, cooking, and household activities.
The chemical isoprene, a reactive compound also found in natural rubber, emerged as the key culprit, with trees identified as its primary urban source.
Isoprene levels in Beijing rivalled those found in temperate forests, largely because many of the city's native tree species -- including the weeping willow and the Chinese white poplar -- are heavy isoprene emitters.
Heat compounds the problem significantly.
Between 20°C and 35°C, the chemical reactivity of VOCs emitted by city trees increased seven to eightfold, the researchers found.
Similar risks may extend across northern China.
Cities such as Harbin and Changchun, which have planted large numbers of willow and poplar trees in recent decades, could face comparable or greater emission levels, scientists noted.
Many cities across Asia and Oceania may also be affected.
European cities appear less exposed, as native tree species there tend to emit monoterpenes – also ozone-forming, but released in smaller quantities than isoprene.
Crucially, the researchers stop well short of calling for less urban greenery or the felling of mature trees.
Instead, they advocate for smarter species selection.
Replacing high-VOC-emitting trees in just one-tenth of Beijing's total tree population with low-emitting alternatives could cut isoprene emissions by at least 29 percent, they calculated.
"Our findings underscore the critical need for selective urban planning in greening programmes to counteract a warming climate," the researchers wrote.
