Fig. 1. FTIR based EM27/SUN spectrometer

Fig. 2. Structure diagram of EM27/SUN

Fig. 3. The flow chart of PROFFAST retrieval algorithm

Fig. 4. Calculated absorption spectroscopy of N₂O by standard atmospheric model

Fig. 5. Time series of XN₂O

Fig. 6. Hourly average daily variation of XN₂O

Fig. 7. XN₂O daily change with MODIS true color map and cloud product data map on November 9，and December 4，2021

Fig. 8. Diurnal time series of variable ground pressure on December 2，2021

Fig. 9. Relative difference of N₂O retrievals with variable pressure used in the PROFFAST algorithm in an exemplary day（December 2，2021）

Fig. 10. Comparison of ground-based EM27/SUN with retrieved data from TCCON

Fig. 11. Measurements of XN₂O with and without correction factors

Fig. 12. XN₂O time series on 2 December 2021 before or after air mass dependence correction

Fig. 13. Correlation between the EM27/SUN and the reference TCCON data for XN₂O in September，November and December