Validation of TROPOMI orbital observations on the total column of carbon monoxide by the ground-based measurements at the OIAP stations in Moscow and Zvenigorod.

Carbon monoxide (CO) total column (TC) measurements of the TROPOMI high-resolution orbital spectrometer have been validated by ground-based spectroscopic measurements at sites of the A.M. Obukhov Institute of Atmospheric Physics RAS (OIAP RAS) in Moscow and Zvenigorod for the period from 06.28.2018 to 12.31.2021. Correlation coefficients (R) between TROPOMI orbital data and ground-based stationary data have been determined and analyzed. For different resolution of satellite data dependence of correlation parameters on the viewing orbital angles, underlying surface albedo and the height of atmospheric boundary layer (ABL) has been investigated. The high values of the correlation coefficient (R ~ 0.81 – 0.97) were obtained depending on the observation point, spatial averaging and applied filtration. The average systematic difference between TROPOMI and ground-based CO TC measurements was -1.1±7.5% (ZSS) and 1.3±5.7% (Moscow) for orbital data resolution 0.1°×0.1°. The correlation coefficients depend on the viewing azimuthal angles and the height of the atmospheric boundary layer. Correlation increase was obtained during observations at viewing azimuthal angles of less than 40º (up to R~0.97), as well as under increase of ABL height (up to R~0.90). For both sites no influence of surface albedo on the correlation parameters of orbital and ground-based measurements has been found. Also, no significant dependence of correlation on the viewing zenith angle has been detected. 
The study was supported by Russian Science Foundation under grant №21-17-00210.