Fig. 1. Geographical location of the ground-based remote sensing observation site. (a) Satellite map of the area near the observation site; (b) schematic diagram of key areas around the observation site

Fig. 2. Examples of dSCD fitting for HCHO (a) and CHOCHO (b)

Fig. 3. Flowchart for inversion of vertical distribution of atmosphere pollutants

Fig. 4. The vertical profile (a) and the near-surface volume fraction profile (b) of formaldehyde (HCHO) retrieved from the single-day observation data on July 30, 2021

Fig. 5. Correlation analysis between HCHO vertical profile volume fraction retrieved from MAX-DOAS and tropospheric HCHO volume fraction from TROPOMI satellite (a) and their trend plot (b)

Fig. 6. Distribution of vertical profiles of formaldehyde (a) and glyoxal (b) in Hefei from July to September 2021

Fig. 7. Vertical profile diagram of formaldehyde volume fraction in a single day. (a) July 14, 2021; (b) July 15, 2021; (c) July 16, 2021; (d) August 1, 2021

Fig. 8. Time series of vertical profile volume fraction of near-surface formaldehyde (a) and glyoxal (b) from July to September 2021

Fig. 9. Diurnal variation of vertical profile volume fraction of formaldehyde (a) and glyoxal (b)

Fig. 10. Average diurnal veriation (a) and average weekly variation (b) of formaldehyde vertical profile volume fraction

Fig. 11. Average diurnal veriation (a) and average weekly variation (b) of glyoxal vertical profile volume fraction

Fig. 12. Correlation analysis of temperature, humidity with formaldehyde (a) (b) and glyoxal (c) (d)

Fig. 13. Time series of the ratio of glyoxal to formaldehyde (RGF) from July to September 2021 (a) and its correlation with nitrogen dioxide volume fraction (b)