Validation of Aura-OMI QA4ECV NO2 Climate Data Records with
ground-based DOAS networks: role of measurement and
comparison uncertainties
Compernolle, S., Verhoelst, T.,
Pinardi, G., Granville, J., Hubert, D., Keppens, A., Niemeijer, S.,
Rino, B., Bais, A., Beirle, S., Boersma, K.F., Burrows, J.P.,
De Smedt, I., Eskes, H., Goutail, F., Hendrick, F., Lorente, A.,
Pazmino, A., Piters, A., Peters, E., Pommereau, J.-P., Remmers, J.,
Richter, A., van Geffen, J., Van Roozendael, M., Wagner, T. and
Lambert, J.-C.: 2020,
Atmos. Chem. Phys. 20, 8017-8045.
Abstract
The QA4ECV (Quality Assurance for Essential Climate Variables) version 1.1
stratospheric and tropospheric NO2 vertical column density (VCD) climate
data records (CDRs) from the OMI (Ozone Monitoring Instrument) satellite
sensor are validated using NDACC (Network for the Detection of Atmospheric
Composition Change) zenith-scattered light differential optical absorption
spectroscopy (ZSL-DOAS) and multi-axis DOAS (MAX-DOAS) data as a reference.
The QA4ECV OMI stratospheric VCDs have a small bias of
~0.2 Pmolec.cm^-2 (5%-10%) and a dispersion of 0.2 to
1 Pmolec.cm^-2 with respect to the ZSL-DOAS measurements. QA4ECV
tropospheric VCD observations from OMI are restricted to near-cloud-free
scenes, leading to a negative sampling bias (with respect to the
unrestricted scene ensemble) of a few peta molecules per square centimetre
(Pmolec.cm^-2) up to -10 Pmolec.cm^-2 (-40%) in one extreme
high-pollution case. The QA4ECV OMI tropospheric VCD has a negative bias
with respect to the MAX-DOAS data (-1 to -4 Pmolec.cm^-2), which is a
feature also found for the OMI OMNO2 standard data product. The tropospheric
VCD discrepancies between satellite measurements and ground-based data
greatly exceed the combined measurement uncertainties. Depending on the
site, part of the discrepancy can be attributed to a combination of
comparison errors (notably horizontal smoothing difference error),
measurement/retrieval errors related to clouds and aerosols, and the
difference in vertical smoothing and a priori profile assumptions.
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created: 10 July 2020
last modified: 19 August 2020