A groundbreaking study published in Science Advances reveals that plants—especially in densely vegetated or urban green spaces—can emit volatile organic compounds (VOCs) that contribute to air pollution under certain environmental conditions. These compounds, such as isoprene and monoterpenes, are naturally released by leaves but can react with sunlight and other pollutants to form ground-level ozone and secondary organic aerosols, key components of smog. The research, conducted by scientists from the University of California, Berkeley and the Max Planck Institute, highlights that heatwaves and elevated nitrogen oxide levels in cities can amplify this effect, making trees and plants an unexpected contributor to urban pollution.
While vegetation generally improves air quality by absorbing CO₂ and filtering particulates, the study urges cities to rethink species selection in urban greening projects. For example, high-VOC emitters like oaks and poplars may worsen ozone formation in polluted urban environments, particularly during extreme heat. The researchers suggest that planting low-emitting species and improving overall urban air quality could help balance the benefits of greenery with unintended atmospheric consequences. As cities expand green infrastructure to combat climate change, these findings underscore the need for a science-informed approach to urban reforestation and air pollution management. More