Downtown LA’s Silent Killer: Study Finds Trees Drive Air Pollution
Despite massive strides in reducing vehicle emissions, a groundbreaking study led by the University of California, Berkley, has shed light on a concerning issue – massive urban tree canopies across Los Angeles, and potentially other major cities, are contributing to persistently high air pollution levels.
California’s 173 million urban canopy has been identified as a hidden source of pollution, leading to a significant increase in “secondary source” emissions as climate change intensifies. The research, spearheaded by Eva Pfannerstill from the University of California, Berkley, has highlighted the impact of urban trees on pollution levels, which continue to pose a challenge despite the rapid decline in vehicle emissions over the past 15 years.
The study, published in Science under the title ‘Temperature-dependent emissions dominate aerosol and ozone formation in Los Angeles,’ points out that while major strides have been made in reducing urban pollution in North American and European cities, there is still much to uncover about the root causes of pollution.
California, known for its pioneering green policies, has been investing significantly in afforestation and tree planting to enhance its urban tree canopy, currently standing at 15%. However, Dr. Pfannerstill, an atmospheric chemist, warns that approximately 60% of ozone and secondary organic aerosol formation potential in summertime Los Angeles is attributed to biogenic terpenoid emissions, with this contribution escalating with rising temperatures.
Recent studies have revealed that urban trees and plants release Biogenic Volatile Organic Compounds (BVOCs), volatile organic compounds emitted by plants and trees. Researchers argue that the trees and shrubs planted to beautify city streets are inadvertently maintaining pollution levels at a high level across Los Angeles and other major cities like San Francisco, San Diego, and Sacramento.
To map these emissions, a team of US researchers conducted airborne measurements over Los Angeles in June 2021. They directly monitored fluctuating concentrations of volatile organic compounds (VOCs), which serve as precursors to particulate and ozone pollution originating from plants. Unlike previous methods that relied on estimations or models, this airborne approach provided direct measurements of airborne pollutants, offering valuable insights into the impact of urban vegetation on air quality.
