Beijing's Isoprene-Emitting Trees Highlight Ozone Risks in Greener, Hotter Cities
Researchers found vegetation produced 52% of the chemicals that form ozone, even though human activities emitted more total volatile organic compounds.
- A new study published in Science Advances finds urban trees in Beijing contribute significantly to ozone formation, with researchers identifying that compounds released by these plants substantially impact air quality in cities.
- Ozone forms when volatile organic compounds from vegetation react with nitrogen oxides in sunlight. Native species including Willow and Populus trees release high levels of isoprene, a major contributor to this chemical process.
- In Beijing, researchers using a 102m platform found vegetation accounted for 52% of ozone-forming chemicals. Roughly 35% of the city's trees are isoprene emitters, with heat increasing chemical reactivity sevenfold between 20°C and 35°C.
- City officials could replace one-tenth of Beijing's high-emitting trees with low-emitting species to reduce isoprene emissions by at least 29 per cent, researchers suggest. This targeted approach could improve urban air quality significantly.
- Rising global temperatures exacerbate the problem as vegetation's chemical reactivity surges in hot weather. Similar air-quality pressures face cities in Asia and Oceania, including Sydney and Melbourne, where many trees also emit isoprene.
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Beijing's isoprene-emitting trees highlight ozone risks in greener, hotter cities
Amid current heat waves, urban greening is once again moving to the center of public debate. Greener cities are generally expected to have cleaner air because trees capture airborne particles, absorb gaseous pollutants and cool urban neighborhoods. But trees also emit biogenic volatile organic compounds (BVOCs) that, in the presence of sunlight and nitrogen oxides (NOx), can contribute to ground-level ozone formation.
Tree selection in urban greening shapes air quality for global cities
Abstract Mitigating ozone pollution remains a pressing challenge for megacities worldwide. Biogenic volatile organic compounds (VOCs) are proposed as pivotal precursors to urban ozone formation. However, direct observational evidence is scarce and the extent of this effect across cities is unclear. Here, by combining an unprecedented eddy covariance flux dataset from Beijing with modeling analysis, we find that urban vegetation contributes over …
City trees cool streets and bind air pollutants. But measurements from Beijing show that isoprenic tree species release disproportionately many reactive organic gases in heat, which together with nitrogen oxides and sunlight can promote ground-level ozone. Therefore, it is not only important how much green a city has, but also which tree species grow there. Innsbruck (Austria). City green is an important building block against summer heat and po…
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