Fine-particle pollution and urban tree emissions alter plant chemistry
PM2.5 pollution was found to weaken the water-use efficiency gains plants derive from rising carbon dioxide, while a separate Beijing study shows willows and poplars supply over half the city's ozone-forming reactivity.
Science··Midday
Share of urban trees in ozone formation
Air samples collected across Beijing between May and July of 2021 show that urban vegetation accounts for about 10 percent of the city's volatile organic compounds, but supplies 52 percent of the reactivity that goes on to form ozone. According to the peer-reviewed study published in Science Advances, this reactivity is driven primarily by isoprene emitted by willows and poplars, which make up roughly 35 percent of the city's trees. The study found that this reactivity rises sharply with increasing air temperature.[1]
Chemical impact of rising temperatures
A rise in temperature to 35 °C increases the hydroxyl reactivity of plant-derived compounds by 7 times compared to 20 °C, lifting vegetation's share of that reactivity from 21 percent to 74 percent. This rate is even higher in some of the 24 megacities the team examined; researchers determined that in Sydney, for instance, about 65 percent of trees emit isoprene. Co-author Bin Yuan notes that the results were initially surprising even to the team.[1]
Particle pollution and water-use efficiency
In a separate study published in Nature Climate Change, PM2.5 pollution was shown to weaken the water-use efficiency gains plants have derived from rising carbon dioxide in recent years. Combining tree-ring isotopes, flux measurements, and satellite data, the team found that the pollution suppresses photosynthesis by reducing the usable light that reaches leaves; the authors argue that current ecosystem models miss this effect because they leave aerosol processes out.[2]
