EOS-Aura/OMI NO2 slant column retrieval: stability & uncertainties
TROPOMI : Introduction OMI : Introduction

Introduction

An initial study into the stability and uncertainties of the EOS-AURA/OMI NO₂ slant column density (SCD) retrieval was presented by Zara et al., 2018, which covers NO₂ retrieval data up to 31 Dec. 2015.

These pages provide an update of that analysis as well as additional analysis results using NO₂ data of the collection 4 (re)processed data, starting from 1 Oct. 2004 up to the end of 2022.

The results presented here are manually updated and currently
cover the NO₂ SCD retrieval results up to: 31 Dec. 2025

Note: The data presented are from a preliminary version of the collection 4 data. The final version of the data, extending to the end of the OMI mission, will be presented here in due time -- differences are, however, expected to be small.

 

Contents

• Row anomaly
• Wavelength calibration of the radiance
• SCD error estimate & statistical uncertainty
• Stripe correction amplitude   --   to come
• Vertical NO₂ column monitoring   --   to come

 

Data selection for the analysis

As in Zara et al., 2018 for OMI van Geffen et al., 2020 for TROPOMI, the analysis is based on orbits over the Pacific Ocean (i.e. away from anthropogenic sources of NO₂): for each day the last orbit is selected, provided that orbit has a satellite (nadir viewing) equator crossings west of about -130°. Such a Pacific Ocean orbit is missing on several few days, in particular during the periods when OMI was measuring in zoom mode, and these days are therefore skipped.

Two latitude ranges are used, depending on the type of analysis:

• The "Tropical Latitude" (TL) range:
  all scanlines that have their sub-satellite latitude point -- corresponding approximately to the nadir viewing detector rows -- within a 30° range that moves along with the seasons, in an attempt to filter out seasonality in the NO₂ data (on 1 January the TL range covers [-30°:0°], while half a year later it covers [0°:+30°]); with this moving range, the solar zenith angle remains more or less the same throughout the year.
• The "Pacific Ocean" (PO) range:
  all groundpixels that have a central latitude within [-60°:+60°].

Slant and vertical NO₂ column values are given here in the SI unit mol/m2 (as in the OMI collection 4 data files) and in several places also in the more commenly unit molecules/cm2; the conversion factor between these two is 6.02214e19. For example, 10.0 μmol/m2 corresponds to 6.022+14 molecules/cm2, and 2.0e15 molecules/cm2 corresponds to 33.211 μmol/m2.

 

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References

• Zara, M., Boersma, K.F., De Smedt, I., Richter, A., Peters, E., Van Geffen, J.H.G.M., Beirle, S., Wagner, T., Van Roozendael, M., Marchenko, S., Lamsal, L. and Eskes, H.J., 2018:
  "Improved slant column density retrieval of nitrogen dioxide and formaldehyde for OMI and GOME-2A from QA4ECV: intercomparison, uncertainty characterization, and trends,"
  Atmos. Meas. Tech. 11, 4033-4058.  ==>  On-line paper  |  PDF file (11 MB)

• van Geffen, J.H.G.M., Boersma, K.F., Eskes, H.J., Sneep, M., ter Linden, M., Zara, M. and Veefkind, J.P.: 2020,
  "S5P/TROPOMI NO₂ slant column retrieval: method, stability, uncertainties and comparisons with OMI,"
  Atmos. Meas. Tech. 13, 1315-1335.  ==>  On-line paper  |  PDF file (8 MB)

• The OMI collection 4 NO₂ Algorithm Theoretical Basis Document [ATBD] -- in preparation

last modified: 26 June 2026
Contact: Jos van Geffen   < geffen [at] knmi [dot] nl >
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