Retrieval of NO2 Tropospheric Column from Ground-Based FTIR Measurements of Direct Solar Radiation

— Based on the analysis of high-resolution FTIR spectra recorded at the atmospheric monitoring station of St. Petersburg State University during 2009–2022, a possibility of deriving the NO 2 tropospheric column from ground-based measurements of direct solar radiation in the mid-IR range is studied. The best agreement (correlation coefficient r = 0.68) with simultaneous DOAS measurements of the NO 2 tropospheric column at the same monitoring station is provided by a retrieval technique based on the use of the spectral range 2914.30–2914.85 cm −1 in combination with the Tikhonov–Phillips regularization. It is shown that FTIR measurements make it possible to reliably detect high levels of tropospheric NO 2 at the SPbSU monitoring station. Our results can be used at the FTIR stations of the NDACC network for significant expansion of the geography of tropospheric NO 2 monitoring.