Fig. 1. Retrieval results under elevation of 2° on December 28th, 2013. (a) Retrieval result of SO2; (b) retrieval error at different wavelengths

Fig. 2. Retrieval results of O4 and SO2 under elevation of 3° on December 28th, 2013. (a) Differential optical depth of O4; (b) differential optical depth of SO2; (c) retrieval residual of O4; (d) retrieval residual of SO2

Fig. 3. Retrieval results of VCD of tropospheric SO2. (a) AOD retrieved by MAX-DOAS; (b) measured aerosol profiles and typical aerosol profiles are used as input to obtain VCD of tropospheric SO2

Fig. 4. Retrieval example of SO2 vertical profiles. (a) Priori profile and retrieved profile; (b) comparison between measured result and simulated result

Fig. 5. Temporal series profiles of SO2 vertical column concentration based on MAX-DOAS retrieval

Fig. 6. Correlation analysis on retrieval and measured values of SO2 differential slant column density

Fig. 7. Temporal series profiles of SO2 volume fractions during December 27-31, 2013

Fig. 8. Comparison of SO2 concentration (0-100 m) measured by MAX-DOAS and point instrument results. (a) Hourly mean values; (b) daily mean values