Fig. 1. Matching principle and comparative analysis route between sky radiometer and MODIS aerosol product

Fig. 2. Results of Langley calibration method from 8-period measurements by sky radiometer for Xi'an region in 2016. (a) 2016/02/08 AM; (b) 2016/05/10 AM; (c) 2016/09/10 AM; (d) 2016/09/11 AM; (e) 2016/10/18 AM; (f) 2016/02/02 PM; (g) 2016/05/10 PM; (h) 2016/09/11 PM

Fig. 3. Daily variation and monthly average distribution of Ozone column amount from OMI measurements in 2016. (a) Daily mean values; (b) monthly mean values

Fig. 4. Results of three MODIS inversion algorithms for Xi'an region. (a) Numbers of effective observation samples per month; (b) monthly mean values of AOD

Fig. 5. Variation characteristics of AOD under different wavelengths (N: number of samples)

Fig. 6. Correlation between AODs calculated from sky radiometer and three MODIS inversion algorithms. (a) DT; (b) DB; (c) DT&DB

Fig. 7. Daily comparisons of AODs inverted from three MODIS algorithms and sky radiometer. (a) DT and POM-02; (b) DB and POM-02; (c) DT&DB and POM-02

Fig. 8. AOD differences between three MODIS algorithms and POM-02

Fig. 9. Annual mean distribution of AODs in Guanzhong Plain calculated by DT&DB algorithm

Fig. 10. Seasonal mean distributions of AOD in Xi'an and its surrounding regions calculated by DT&DB algorithm. (a) Spring; (b) summer; (c) autumn; (d) winter

Fig. 11. Histogram of AODs in four seasons in Xi'an and Xianyang regions calculated by DT&DB algorithm