Table 1. Research relevant to the ability to reduce PM of urban trees and forests.

Research topics	Reference
Quantitative analysis of PM by species	Dzierżanowski et al., 2011; Freer-Smith et al., 2005; Hwang et al., 2011; Leonard et al., 2016; Liang et al., 2016; Liu et al., 2012; Liu et al., 2018; Łukowski et al., 2020; Sæbø et al., 2012; Song et al., 2015; Weerakkody et al., 2017; Xu et al., 2018; Xu et al., 2019a
Relationship between leaf traits and PM capture	Chen et al., 2017; Chiam et al., 2019; Sæbø et al., 2012; Sgrigna et al., 2020; Tian et al., 2019; Weerakkody et al., 2018; Zhang et al., 2020; Zhao et al., 2019
Estimating the air purification ability of urban forests	McDonald et al., 2007; Nowak, 2006; Peters and Eiden, 1992; Schaubroeck et al., 2014; Tallis et al., 2011; Yang et al., 2005
Effects of rainfall on PM retention	Xu et al., 2017; Wang et al., 2015b; Weerakkkody et al., 2018; Xie et al., 2019; Zhang et al., 2019
Seasonal variation on PM capturing	He et al., 2020; Sgrigna et al., 2015; Wang et al., 2013
Chemical composition of PM deposited on leaf surfaces	Kardel et al., 2018; Song et al., 2015; Sgrigna et al., 2016; Xu et al., 2019a
PM capturing by different organs of tree	Guéguen et al., 2012; Xu et al., 2019b