Urban forests face dual role in climate and air quality

Research indicates that while urban forests are essential for cooling cities and managing climate crises, certain tree species can inadvertently contribute to air pollution. A study conducted in Beijing by an international team, including researchers from the University of Jinan and the University of Innsbruck, found that species such as willows and poplars release high levels of isoprene, a volatile organic compound (VOC).

When isoprene reacts with nitrogen oxides from traffic and industry in the presence of sunlight, it facilitates the formation of ground-level ozone. While biogenic VOCs accounted for only about 10.7% of total emissions in Beijing, isoprene was responsible for approximately 49% of the measured OH-reactivity, making it a primary driver of ozone formation. This chemical reactivity increases significantly with heat; at 35 degrees Celsius, the reactivity was 700% higher than at 20 degrees Celsius.

Separately, research led by Bangor University emphasizes the need to treat urban forests as critical infrastructure. The study suggests that current policies often lack the necessary funding and scope to protect these green spaces, which are vital for water infiltration, temperature regulation, and biodiversity as urban populations continue to grow.