Fig. 1. Observation instruments. (a) Bruker 125HR FTS; (b) solar-tracker

Fig. 2. Process of spectral retrieval

Fig. 3. Linear alignment results of instrument. (a) MEAs retrieved from HBr cell measurements; (b) PEs retrieved from HBr cell measurements

Fig. 4. Spectral fitting result and residual of HNO₃ in absorption window centered in wavenumber of 869 cm^-1

Fig. 5. Spectral fitting result and residual of HNO₃ in absorption window centered in wavenumber of 873 cm^-1

Fig. 6. Examples of a priori profile and retrieved profile of HNO₃. (a) Retrieved profile and a priori profile; (b) Retrieved profile and a priori profile after taking logarithm

Fig. 7. Vertical profiles of HNO₃ volume concentration in different seasons

Fig. 8. Average kernels of retrieved HNO₃ profiles

Fig. 9. Total-column average kernel of retrieved HNO₃ profiles under typical measurement condition

Fig. 10. Time series of HNO₃ total column in 2017

Fig. 11. Comparison between total column of HNO₃ observed by ground-based FTS and corresponding partial column of HNO₃ observed by MLS satellite

Fig. 12. Scattering plot of total column of HNO₃ observed by ground-based FTS and partial column of HNO₃ observed by MLS satellite