Comparing i-Tree Eco Estimates of Particulate Matter Deposition with Leaf and Canopy Measurements in an Urban Mediterranean Holm Oak Forest

Abstract

Trees and urban forests remove particulate matter (PM) from the air through the deposition of particles on the leaf surface, thus 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. However, model results are seldom validated with experimental data. In this study, we compared i-Tree Eco calculations of PM2.5 deposition with fluxes determined by eddy covariance assessments (canopy scale) and particulate matter accumulated on leaves derived from measurements of vacuum/filtration technique as well as scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (leaf scale). These investigations were carried out at the Capodimonte Royal Forest in Naples. Modeled and measured fluxes showed good overall agreement, demonstrating that net deposition mostly happened in the first part of the day when atmospheric PM concentration is higher, followed by high resuspension rates in the second part of the day, corresponding with increased wind speeds. The sensitivity analysis of the model parameters showed that a better representation of PM deposition fluxes could be achieved with adjusted deposition velocities. It is also likely that the standard assumption of a complete removal of particulate matter, after precipitation events that exceed the water storage capacity of the canopy (Ps), 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 parametrization and the estimate of particulate matter removed by urban trees.

Ecosystem Services Provided By Urban Forests In The Southern Caucasus Region: A Modeling Study In Tbilisi, Georgia

“…In general, evergreen species in Tbilisi, despite an extended leaf-on season and thus the possibility of longer interaction with pollutants and precipitation, are not able to provide more ecosystem services than deciduous species. For example, rainfall is abundant in spring-summer season, which allows for greater ne particulate matter removal (Nowak et al 2013;Pace and Grote, 2020;Pace et al 2021a), as well as greater rain interception and thus reduced runoff (Fig. 3-5).…”

Urban Planning Insights from Tree Inventories and Their Regulating Ecosystem Services Assessment

“…In particular, we choose the i-Tree Eco tool as it has become an international standard in assessing ecosystem services and economic values derived specifically from urban trees. Numerous studies have been conducted to validate this tool through case study applications [20,32,33] and comparison and synergy with other tools such as allometric equations or direct measurements [34][35][36][37][38]. At first, i-Tree Eco has been extensively applied in the USA [39][40][41]; since 2010, it has been widely used in other countries and various climatic regions [32,35,37,42,43], and, in recent years, its use has also been spreading in southern Europe/Mediterranean contexts [33,44,45].…”

“…To achieve this aim, many scholars evaluated that nature inside cities provides multiple ecosystem services. The Millennium Ecosystem Assessment [2] described ecosystem services as "the benefits people obtain from ecosystems" (p. 38), and divided them into supporting, provisioning, regulating, and cultural services. In the urban landscape, trees are essential elements covering 26.5% of urban areas globally, and they provide benefits to the citizens belonging to the four categories of MEA [3].…”

Ecosystem Services Provided by Urban Forests in the Southern Caucasus Region: A Modeling Study in Tbilisi, Georgia

“…A similar result was also observed by Pace et al 2021 [55] in a comparison with sap flow measurements in two squares in Munich, showing that taking into account the soil water balance results in a better match with the assessments by improving the calculation of transpiration and cooling effect of trees. Regarding particulate matter removal, a recent study compared the calculation of i-Tree Eco with the accumulation of fine particulate matter on Quercus ilex leaves measured by vacuum filtration and scanning electron microscopy, highlighting the need to improve the current model parameterization by taking into account the different leaf traits on deposition, resuspension, and washing [56].…”