18 Oct 2021
18 Oct 2021
Status: this preprint is currently under review for the journal AMT.

Horizontal distribution of tropospheric NO2 and aerosols derived by dual-scan multi-wavelength MAX-DOAS measurements in Uccle, Belgium

Ermioni Dimitropoulou1, Francois Hendrick1, Martina Michaela Friedrich1, Frederik Tack1, Gaia Pinardi1, Alexis Merlaud1, Caroline Fayt1, Christian Hermans1, Frans Fierens2, and Michel Van Roozendael1 Ermioni Dimitropoulou et al.
  • 1Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, 1180, Belgium
  • 2IRCEL-CELINE, Brussels, Belgium

Abstract. Dual-scan ground-based Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements of tropospheric nitrogen dioxide (NO2) and aerosols have been carried out in Uccle (50.8° N, 4.35° E; Brussels region, Belgium) for two years, from March 2018 to February 2020. The MAX-DOAS instrument has been operating in both UV and Visible wavelength ranges in a dual-scan configuration consisting of two sub-modes: (1) an elevation scan in a fixed viewing azimuthal direction and (2) an azimuthal scan in a fixed low elevation angle (2°). By analyzing the O4 and NO2 dSCDs at six different wavelength intervals along every azimuthal direction and by applying a new Optimal-Estimation-based inversion approach, the horizontal distribution of the NO2 near-surface concentrations and vertical column densities (VCDs) and the aerosols near-surface extinction coefficient are retrieved along ten azimuthal directions. The retrieved horizontal NO2 concentration profiles allow the identification of the main NO2 hotspots in the Brussels area. Correlative comparisons of the retrieved horizontal NO2 distribution have been conducted with airborne, mobile, and satellite datasets, and overall a good agreement is found. The comparison with TROPOMI observations reveals that the characterization of the horizontal distribution of tropospheric NO2 VCDs by ground-based measurements, the appropriate sampling of TROPOMI pixels, and an adequate a priori NO2 profile shape in TROPOMI retrievals lead to a better consistency between satellite and ground-based datasets.

Ermioni Dimitropoulou et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2021-308', Anonymous Referee #1, 03 Nov 2021
  • RC2: 'Comment on amt-2021-308', Anonymous Referee #2, 04 Feb 2022

Ermioni Dimitropoulou et al.

Ermioni Dimitropoulou et al.


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Short summary
Two years of dual-scan ground-based MAX-DOAS measurements of tropospheric NO2 and aerosols in Uccle (Belgium) have been used to develop a new Optimal-Estimation-based inversion approach to retrieve horizontal profiles of surface NO2 concentration and aerosol extinction profiles. We show that the combination of an appropriate sampling of TROPOMI pixels by ground-based measurements and an adequate a priori NO2 profile shape in TROPOMI retrievals improves the agreement between the two datasets.