Table 1 Deduction of evaluation criteria about available space for urban forest to reduce particulate matter air pollution

Layer 2	Layer 3	Evaluation indexes	Reference
Physical characteristics	Planting ground	Planting ground types	Lee et al.(2008)
	Ground types	Ground types(flat, sloped, mounded)	Hwang et al.(2018), Kim et al.(2017)
	Area or width	Area(m2) or width(m) of the site	Lee et al.(2008)
Locational characteristics	Proximity of source apportionment of particulate matter	Distance from source apportionment of PM10 and PM2.5 to site(m)	Moon et al.(2017)
	Land use	Use districts around the site	Han et al.(2015), Jerrett et al.(2007)
	Building arrangement	Open space and site plan around the site	Hong et al.(2018), Sung et al.(2019)
	Traffic volume	Average daily traffic around the site	Brauer et al.(2003), Jerrett et al.(2007)
Planting type of existing green space	Plantation of existing greenspace	Particulate pollution mitigating ability	Liu et al.(2018), National Institute of Forest Science(2018)
	Planting distance of existing greenspace	Planting distance(m)	Xu and Kim(2017)
	Planting density of existing greenspace	Planting density(tree/m2)	National Institute of Forest Science(2018)
	Planting structures of existing greenspace	Planting structures	Hwang et al.(2018), Kim et al.(2017), Shin et al.(2007), Xu and Kim(2017)
Weather conditions	Wind direction	Main wind direction	Park(2017), Shin et al.(2007)
	Wind speed	Maximum wind speed(m/s)	Lee(2010), Shin et al.(2007), Wise and Comrie(2005)
	Temperature	Maximum temperature(·C)	Lee(2010), Wise and Comrie(2005)
	Humidity	Relative humidity(%)	Lee(2010), Shin et al.(2007), Wise and Comrie(2005)
Human social environment	Disadvantaged groups	Use frequency to disadvantaged groups	Yu et al.(2017)
	Floating population	Number of the floating population	Park et al.(2018)
	Security of site	Land ownership	Kim and Oh(2019)
	Maintenance	Site conditions and management subject	Lee et al.(2008)