Beijing's trees found to be major source of ozone pollution, study says
A study led by Jinan University scientists found that Beijing's poplar and willow trees emit high levels of isoprene, which reacts with nitrogen oxides to produce ground-level ozone. This natural source may be a major contributor to the city's ozone smog, even as vehicle emissions decline. The research was published in the journal Science Advances.
The Jinan University-led team initially set out to measure ozone contributions from human activity, but their instruments pointed unexpectedly toward the city's vegetation. Beijing's poplars and willows, planted over four decades ago for shade, release isoprene at unusually high rates. When this compound mixes with nitrogen oxides from vehicles and factories, ground-level ozone forms, contributing to the city's smog.
The finding helps explain why ozone levels remained stubbornly high even as Beijing's fleet shifted toward electric vehicles. Ozone smog has been a documented public health concern since the 1940s, with severe historical incidents linked to hundreds of deaths. The research, published in Science Advances, drew on international collaboration and challenges assumptions about urban greenery's role in air quality.
This discovery could complicate urban environmental planning, as tree species selection may need to account for chemical emissions alongside shade and aesthetic benefits. Beijing's 20 million residents could face continued ozone exposure despite vehicle electrification efforts, potentially affecting respiratory health and daily life. Municipal authorities may need to weigh ecological benefits against air quality trade-offs when designing future green spaces, though the study's implications extend to other cities