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 NO₂ 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 NO₂ 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 NO₂ 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 NO₂ monitoring.