Table 2.

Site information of Beijing, Xianghe and SDZ.

	Lon	Lat	Year	NA	NM	NF	Purpose
Beijing	116.38	39.97	2002–2014	2977	2397	3367	Model development
SDZ	117.12	40.65	2005–2011	1866	1277	1735	Validation
Xianghe	116.96	39.75	2005–2011	1840	1262	1894	Validation

(Noted: N_A, N_M, N_F represent AOD sampling by AERONET, MODIS and AERONET-MODIS fusion, respectively).