Unequal Canopies, Unequal Benefits: Environmental Justice Implications of Street Tree Air Pollution Mitigation

Air pollutants can penetrate deep into the lungs, enter the bloodstream, and trigger a cascade of cardiovascular diseases. Elevated pollutant levels in cities are often associated with heavy traffic and industrial emissions, highlighting the need for effective mitigation strategies. Street trees can reduce air pollution through dry deposition, whereby particles are captured by tree canopies in the absence of precipitation. However, city-level models typically assume uniform deposition rates and neglect location-specific variation in tree benefits. Here, we designed a social-ecological systems approach (SES) and revealed substantial spatial disparities in tree-derived air quality benefits within a city. We found that communities with lower urban canopy received fewer air quality benefits. To address these differences, priority tree planting sites were determined using a stepwise framework that takes into account both neighbourhood-level population exposure and social vulnerability. Our findings demonstrate the uneven distribution of urban ecosystem services, emphasizing the importance of integrating environmental justice into urban forestry planning and provide practical guidance on optimizing planting for reducing population exposure to air pollutants.