“…There are extensive studies investigating the PM2.5-AOD relationship by the use of either an empirical statistical method (Engel-Cox et al, 2004;Liu et al, 2005Liu et al, , 2009Gupta et al, 2006;Koelemeijer et al, 2006;Gupta and Christopher, 2008;Paciorek et al, 2008;Di Nicolantonio et al, 2009;Schaap et al, 2009;Lee et al, 2012;Sorek-Hamer et al, 2013;Strawa et al, 2013;Chudnovsky et al, 2014;Ma et al, 2014) or a chemical transportation model (Liu et al, 2004;Van Donkelaar et al, 2006Kessner et al, 2013;Xu et al, 2015). In these studies, aerosol vertical distributions are estimated based on model simulation or under an assumption that aerosols are well mixed within the boundary layer and then decrease exponentially with height.…”