10 May 2021

10 May 2021

Review status: this preprint is currently under review for the journal ACP.

Comparative assessment of TROPOMI and OMI formaldehyde observations against MAX-DOAS network column measurements

Isabelle De Smedt1, Gaia Pinardi1, Corinne Vigouroux1, Steven Compernolle1, Alkis Bais2, Nuria Benavent3, Folkert Boersma4,5, Ka-Lok Chan6, Sebastian Donner7, Kai-Uwe Eichmann8, Pascal Hedelt6, François Hendrick1, Hitoshi Irie9, Vinod Kumar7, Jean-Christopher Lambert1, Bavo Langerock1, Christophe Lerot1, Cheng Liu10, Diego Loyola6, Ankie Piters4, Andreas Richter8, Claudia Inés Rivera Cárdenas11, Fabian Romahn6, Robert George Ryan12,13, Vinayak Sinha14, Nicolas Theys1, Jonas Vlietinck1, Thomas Wagner7, Ting Wang15, Huan Yu1, and Michel Van Roozendael1 Isabelle De Smedt et al.
  • 1Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Ringlaan 3, 1180 Uccle, Belgium
  • 2Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki (AUTH), Thessaloniki, Greece
  • 3Department of Atmospheric Chemistry and Climate, Institute of Physical Chemistry Rocasolano (CSIC), Madrid, Spain
  • 4Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands
  • 5Meteorology and Air Quality group, Wageningen University, the Netherlands
  • 6Institut für Methodik der Fernerkundung (IMF), Deutsches Zentrum für Luft und Raumfahrt (DLR), Oberpfaffenhofen, Germany
  • 7Max-Planck-Institut für Chemie (MPI-C), Mainz, Germany
  • 8Institute of Environmental Physics, University of Bremen (IUP-B), Bremen, Germany
  • 9Center for Environmental Remote Sensing, Chiba University (Chiba U), Chiba, Japan
  • 10Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, China
  • 11Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México (UNAM), Mexico City, Mexico
  • 12School of Earth Sciences, The University of Melbourne, Melbourne, Australia
  • 13ARC Centre of Excellence for Climate System Science, Sydney, Australia
  • 14Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research (IISER), Mohali, India
  • 15Institute of Atmospheric Physics, Chinese Academy of Sciences (CAS), Beijing, China

Abstract. The TROPOspheric Monitoring Instrument (TROPOMI), launched in October 2017 on board the Sentinel-5 Precursor (S5P) satellite, monitors the composition of the Earth's atmosphere at an unprecedented horizontal resolution as fine as 3.5 × 5.5 km2. This paper assess the performances of the TROPOMI formaldehyde (HCHO) operational product compared to its predecessor, the OMI HCHO QA4ECV product, at different spatial and temporal scales. The parallel development of the two algorithms favored the consistency of the products, which facilitates the production of long-term combined time series. The main difference between the two satellite products is related to the use of different cloud algorithms, leading to a positive bias of OMI compared to TROPOMI of up to 30 % in Tropical regions. We show that after switching off the explicit correction for cloud effects, the two datasets come into an excellent agreement. For medium to large HCHO vertical columns (larger than 5 × 1015−2) the median bias between OMI and TROPOMI HCHO columns is not larger than 10 % (< 0.4 × 1015−2). For lower columns, OMI observations present a remaining positive bias of about 20 % (< 0.8 × 1015−2) compared to TROPOMI in mid-latitude regions. Here, we also use a global network of 18 MAX-DOAS instruments to validate both satellite sensors for a large range of HCHO columns. This work complements the study by Vigouroux et al. (2020) where a global FTIR network is used to validate the TROPOMI HCHO operational product. Consistent with the FTIR validation study, we find that for elevated HCHO columns, TROPOMI data are systematically low (−25 % for HCHO columns larger than 8 × 1015−2), while no significant bias is found for medium range column values. We further show that OMI and TROPOMI data present equivalent biases for large HCHO levels. However, TROPOMI significantly improves the precision of the HCHO observations at short temporal scales, and for low HCHO columns. We show that compared to OMI, the precision of the TROPOMI HCHO columns is improved by 25 % for individual pixels, and up to a factor 3 when considering daily averages in 20 km-radius circles. The validation precision obtained with daily TROPOMI observations is comparable to the one obtained with monthly OMI observations. To illustrate the improved performances of TROPOMI in capturing weak HCHO signals, we present clear detection of HCHO column enhancements related to shipping emissions in the Indian Ocean. This is achieved by averaging data over a much shorter period (3 months) than required with previous sensors, and opens new perspectives to study shipping emissions of VOCs and related atmospheric chemical interactions.

Isabelle De Smedt et al.

Status: open (until 05 Jul 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of acp-2021-378', Anonymous Referee #1, 03 Jun 2021 reply
  • RC2: 'Comment on acp-2021-378', Anonymous Referee #2, 11 Jun 2021 reply

Isabelle De Smedt et al.

Isabelle De Smedt et al.


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Short summary
This paper assess the performances of the TROPOMI formaldehyde observations compared to its predecessor OMI at different spatial and temporal scales. We also use a global network of MAX-DOAS instruments to validate both satellite datasets for a large range of HCHO columns. The precision obtained with daily TROPOMI observations is comparable to monthly OMI observations. We present clear detection of weak HCHO column enhancements related to shipping emissions in the Indian Ocean.