Ground-Based Remote Sensing of Total Columnar CO₂, CH₄, and CO Using EM27/SUN FTIR Spectrometer at a Suburban Location (Shadnagar) in India and Validation of Sentinel-5P/TROPOMI

Greenhouse gases (GHGs) play an important role in controlling local air pollution as well as climate change. In this study, we retrieved column-averaged dry-air ( $X$ ) mole fractions of carbon dioxide (CO ₂ ), methane (CH ₄ ), and carbon monoxide (CO) using a ground-based EM27/SUN Fourier transform infrared spectrometer (FTIR). The EM27/SUN spectrometers are widely in use in the COllaborative Carbon Column Observing Network (COCCON). The PROFFAST software provided by COCCON has been used to analyze the measured atmospheric solar absorption spectra. In this letter, the diurnal variation and the time series of daily averaged $X$ CO ₂ , $X$ CH ₄ , and $X$ CO covering the period from December 2020 to May 2021 are analyzed. The maximum values of $X$ CO ₂ , $X$ CH ₄ , and $X$ CO are observed to be 420.57 ppm, 1.93 ppm, and 170.40 ppb, respectively. Less diurnal but clear seasonal changes are observed during the study period. $X$ CH ₄ and $X$ CO from the Sentinel-5Precursor (S5P)/TROPOspheric Monitoring Instrument (TROPOMI) are compared against the EM27/SUN retrievals. The correlation coefficient for the EM27/SUN retrieved $X$ CH ₄ and $X$ CO, with the S5P/TROPOMI products, are 0.75 and 0.94, respectively.