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Trees and urban forests remove particulate matter (PM) from the air through the deposition of particles on the leaf surface helping to improve air quality and reduce respiratory problems in urban areas. Leaf deposited PM, in turn, is either resuspended back into the atmosphere, washed off during rain events or transported to the ground with litterfall. The net amount of PM removed depends on crown and leaf characteristics, air pollution concentration, and weather conditions, such as wind speed and precipitation. Many existing deposition models, such as i-Tree Eco, calculate PM2.5 removal using a uniform deposition velocity function and resuspension rate for all tree species, which vary based on leaf area and wind speed. This study compared i-Tree Eco calculations of PM2.5 deposition with fluxes determined by canopy scale and particulate matter accumulated on leaves at the Capodimonte Royal Forest in Naples. Modeled and measured fluxes showed good overall agreement, but the sensitivity analysis of the model parameters showed that a better representation of PM deposition fluxes could be achieved with adjusted deposition velocities and the standard assumption of a complete removal of particulate matter, after the water storage capacity of the canopy should be reconsidered to better account for specific leaf traits. These results represent the first validation of i-Tree Eco PM removal with experimental data and are a starting point for improving the model.

Keywords: i-Tree Eco, urban forests, trees, particulate matter, air quality

Rocco Pace; Gabriele Guidolotti; Chiara Baldacchini; Emanuele Pallozzi; Rüdiger Grote; David J. Nowak; Carlo Calfapietra

(2021). Environmental Science & Technology, USDA Forest Service, Northern Research Station

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