09 Jan 2023
09 Jan 2023
Status: this preprint is currently under review for the journal AMT.

Ground-based MAX-DOAS observations of NO2 and H2CO at Kinshasa and comparisons with TROPOMI observations

Rodriguez Yombo Phaka1,3, Alexis Merlaud2, Gaia Pinardi2, Martina M. Friedrich2, François Hendrick2, Jean-François Müller2, Jenny Stavrakou2, Isabelle De Smedt2, Ermioni Dimitropoulou2, Richard Bopili Mbotia Lepiba3, Edmond Phuku Phuati3, Buenimio Lomami Djibi3, Lars Jacob2, Caroline Fayt2, Michel Van Roozendael2, Jean-Perre Mbungu Tsumbu3, and Emmanuel Mahieu1 Rodriguez Yombo Phaka et al.
  • 1Institut d’Astrophysique et de Geophysique, UR SPHERES, Université de Liège, Liège, Belgique
  • 2Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
  • 3Université de Kinshasa, Faculté des Sciences/Dpt de Physique, Kinshasa, RDC

Abstract. We present a database of MAX-DOAS (Multi-AXis Differential Optical Absorption Spectroscopy) ground-based observations of NO2 and H2CO performed for the first time in the city of Kinshasa. These measurements were conducted between November 2019 and July 2021 and processed using the standardized inversion tools developed in the ESA FRM4DOAS (Fiducial Reference Measurements for Ground-Based DOAS Air-Quality Observations) project. The retrieved geophysical quantities are used to validate column observations from the TROPOspheric Monitoring Instrument (TROPOMI) in Kinshasa. In the validation, we experiment three different comparison cases of increasing complexity. In the first case, a direct comparison between MAX-DOAS observations (average +/- 60 minutes around overpass) and TROPOMI shows an underestimation of TROPOMI with a median bias of -40 % (s=0.26 and R=0.41) for NO2 and -26 % (s=0.24 and R=0.28) for H2CO. The second case takes into account the different vertical sensitivities of the two instruments and the apriori profile. We note a slight decrease of the biases and a strong improvement of the linear regression parameter, about -35 % (s=0.72 and R=0.74) for NO2 and 1 % (s=1.01 and R=0.66) for H2CO. The third case, which is considered more realistic than the first two, builds on the second case by considering also the direction of sight of the MAX-DOAS. For this third case, we find a bias of -2 % (s= 1.09; R= 0.59) for NO2 and 13 % (s= 1.51; R= 0.60) for H2CO. Those results indicate a large impact of the vertical sensitivity and horizontal heterogeneity in this validation process at this site. In order to evaluate the capability of the GEOS-Chem model in this region, we performed the comparisons between TROPOMI and the simulations made for 2020. We found a bias of 16 % (s= 0.42 and R = 0.80) for NO2 and bais of 61 % (s= 0.05 and R = 0.24) for H2CO.

Rodriguez Yombo Phaka et al.

Status: open (until 23 Feb 2023)

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Rodriguez Yombo Phaka et al.

Rodriguez Yombo Phaka et al.


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Short summary
We present air quality measurements in Kinshasa, Democratic Republic of the Congo, performed with a newly developed instrument which was installed on a roof of the University of Kinshasa in November 2019. The instrument records spectra of the scattered sun light, from which we derive the abundances of nitrogen dioxide and formaldehyde, two important pollutants. We compare our ground-based measurements with those of a satellite, namely TROPOMI; and TROPOMI with a chemistry model, GEOS-Chem.