Table 5.

Summary of relevant studies that have quantified the linkage between GI, air pollutant reduction and health benefits.

Author (year)	City; Model used	Summary
Tiwary et al.(2009)	London (UK); (ADMS-Urban + statistical model)	• PM₁₀ removal has been estimated through different GI combinations with two species (sycamore maple (Acer pseudoplatanus L.), Douglas fir (Pseudotsuga menziesii Franco) and grassland using computational model. • PM₁₀ reduction varied between 0.03 to 2.33 t ha yr⁻¹ with different GI combination. • The health effects noted were a reduction in 2 premature deaths per year and 2 respiratory hospital admissions per year.
Powe and Willis (2004)	Britain(UK); (Monitoring stations+ statistical model)	• The absorption of SO₂ and PM₁₀ via forests (more than 2 ha in area) were estimated based on National Air Quality Information and Forest Commission spatial distribution data of woodland. • The forest can absorb large quality of air pollutants, for example, 385,695–596,916 metric tonnes of PM₁₀ and 7715–11,215 metric tonnes of SO₂ per year • The above air pollutants reduction would be equal to 5–7 deaths per year and 4–6 hospital admission per year.
David J. Nowak et al.(2013)	10 U.S. cities; (Monitoring stations + i-Tree)	• PM_2.5 removal was estimated for 10 U.S. cities with existing trees cover using i-Tree model and U.S. EPA monitors concentration. • Total amount of PM_2.5 removal varies from 4.7 to 64.5 tonnes per year. • The equivalent mortality reduction from 0.1 to 7.6 death per year.
Nowak et al.(2018)	86 Canada cities; (Monitoring stations + i-Tree)	• The change in air pollutants (NO₂, O₃, PM_2.5, SO₂, and CO) concentration have been estimated through the iTree model and health impacts were studied. • The total air pollutant removal was 7500 t to 21,100 t and average removal rate was 3.72 g/m2/year. • The overall health impacts of urban trees are included avoidance of 30 human mortality in all cities.
Hirabayashi and Nowak (2016)	U.S.; (Monitoring stations + i-Tree)	• Resultant changes in concentration for the four air pollutants (NO₂, O₃, PM_2.5 and SO₂) were modelled by the iTree model using deciduous and evergreen trees with varying LAI and 2010 census data. US EPA’s BenMAP has been used to link air quality improvement to human health improvement was estimated. • In urban areas, annual mean air pollutant concentration was 15.5 (μgm⁻³) for NO₂, 61.7(μgm⁻³) for O₃, 10.0 (μgm⁻³) for PM_2.5 and 4.9 (μgm⁻³) for SO₂. Changes in concentration increased as the LAI increased but the relation is non-linear. • A comprehensive national database of deciduous and evergreen trees with varying LAI and its effects on air quality and human health in the United States was developed
Nowak et al.(2014)	U.S.; (Monitoring stations + i-Tree)	• Avoidable health impacts and associated economic benefits of four air pollutants (NO₂, O₃, PM_2.5 and SO₂) removal by trees and forest in the US were estimated for 2010. • The estimated quantity of air pollutants removal was 17.4 million tonnes based on hourly pollution data and daily total tree cover and LAI though i-Tree model. • The existing trees can help in avoiding more than 850 incidences of human mortality and 670,000 incidences of acute respiratory symptoms.
Rao et al.(2014)	Portland; (Monitoring stations + LUR)	• LUR have been used to estimate a decrease in NO₂ concentration by an urban tree in Portland. • The estimated removal of NO₂ was 0.57 ppb for every 10 ha trees. • The annual health benefits are approximately 21,000 fewer incidences and 7000 fewer days of missed school due to asthma exacerbation for 4–12 year-olds; 54 fewer emergency visits across people of all ages; and 46 fewer cases of hospitalization due to respiratory problems triggered by NO₂ in the elderly. • The potential of an urban forest to reduce the air pollutant (NO₂) and hence provide health benefits are approximately 7 million USD due to reduced incidence of respiratory problems.
Bodnaruk et al.(2017)	Baltimore (US); (Monitoring station + i-Tree)	• The monetary benefits of increasing tree cover from 24% to 40% have been estimated under different spatial GI distribution. • An additional annual 173 ton air pollutants removal was predicted at maximum potential tree cover of 44.4%. • The monetary benefits of these air pollutant removal on human health were estimated equal to 6.3 million USD.
City of Woodland (2018)	Woodland (California); (Remote sensing + i-Tree)	• The total air pollutants removal and monetary benefits of existing 14.5% urban tree canopy have been assessed using high-resolution aerial imagery and remote sensing software for 2010. The U.S. EPA’s BenMAP Model was used to estimate monetary values resulting from changes in air pollutants concentration. • The analysis estimated that Woodland’s tree canopy annually removing 40 tons of air pollutants (includes CO, NO₂, O₃, SO₂ and PM₁₀) and save 15.3 million gallons of stormwater. • The monetary values of health benefits resulting from air pollutants removal have been estimated as equal to 1.8 million USD.
City of Sacramento (2018)	Sacramento (California); (Remote sensing + i-Tree)	• The U.S. EPA’s BenMAP Model was used to estimate monetary values resulting from air pollutants removal. These removals have been estimated using highresolution aerial imagery and remote sensing software for existing 19.1 % urban tree canopy in 2010. • The analysis estimated that Sacramento’s tree canopy annually removing 392.4 tons of air pollutants (includes CO, NO₂, O₃, SO₂ and PM₁₀) and save 58 million gallons of stormwater. • The monetary values of health benefits resulting from air pollutants removal have been estimated as equal to 18.8 million USD.