| Summary: | To assess the best measures for the improvement of air quality, it is crucial to investigate in situ and columnar pollution levels. In this study, ground-based measurements of nitrogen dioxide (NO<sub>2</sub>) and ozone (O<sub>3</sub>) collected in Rome (Italy) between 2017 and 2022 are analyzed. Pandora sun-spectrometers provided the time series of the NO<sub>2</sub> vertical column density (VC-NO<sub>2</sub>), tropospheric column density (TC-NO<sub>2</sub>), near-surface concentration (SC-NO<sub>2</sub>), and the O<sub>3</sub> vertical column density (VC-O<sub>3</sub>). In situ concentrations of NO<sub>2</sub> and O<sub>3</sub> are provided by an urban background air quality station. The results show a clear reduction of NO<sub>2</sub> over the years, thanks to the recent ecological transition policies, with marked seasonal variability, observable both by columnar and in situ data. Otherwise, O<sub>3</sub> does not show inter-annual variations, although a clear seasonal cycle is detectable. The results suggest that the variation of in situ O<sub>3</sub> is mainly imputable to photochemical reactions while, in the VC-O<sub>3</sub>, it is triggered by the predominant contribution of stratospheric O<sub>3</sub>. The outcomes highlight the importance of co-located in situ and columnar measurements in urban environments to investigate physical and chemical processes driving air pollution and to design tailored climate change adaptation strategies.
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