Validation of Sentinel-5P TROPOMI tropospheric NO2 products by comparison with NO2 measurements from airborne imaging DOAS, ground-based stationary DOAS, and mobile car DOAS measurements during the S5P-VAL-DE-Ruhr campaign

Airborne imaging differential optical absorption spectroscopy (DOAS), ground-based stationary DOAS, and car DOAS measurements were conducted during the S5P-VAL-DE-Ruhr campaign in September 2020. The campaign area is located in the Rhine-Ruhr region of North Rhine-Westphalia, western Germany, which...

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Published in:Atmospheric measurement techniques 2023-03, Vol.16 (5), p.1357-1389
Main Authors: Lange, Kezia, Richter, Andreas, Schönhardt, Anja, Meier, Andreas C, Bösch, Tim, Seyler, André, Krause, Kai, Behrens, Lisa K, Wittrock, Folkard, Merlaud, Alexis, Tack, Frederik, Fayt, Caroline, Friedrich, Martina M, Dimitropoulou, Ermioni, Michel Van Roozendael, Kumar, Vinod, Donner, Sebastian, Dörner, Steffen, Lauster, Bianca, Razi, Maria, Borger, Christian, Uhlmannsiek, Katharina, Wagner, Thomas, Ruhtz, Thomas, Eskes, Henk, Bohn, Birger, Daniel Santana Diaz, Abuhassan, Nader, Schüttemeyer, Dirk, Burrows, John P
Format: Article
Language:English
Subjects:
Absorption spectroscopy
Aerosols
Air pollution
Air pollution measurements
Airborne sensing
Aircraft
Algorithms
Analytical methods
Bias
Chemistry
Cloud height
Clouds
Coefficients
Correlation coefficient
Correlation coefficients
Datasets
Ground stations
Imaging
Imaging techniques
Instruments
Meteorological conditions
Microprocessors
Monitoring instruments
Nitrogen dioxide
Pollution
Power plants
Reflectance
Remote sensing
Resolution
Retrieval
Satellites
Slopes
Spatial discrimination
Spatial resolution
Spectroscopy
Troposphere
Vertical profiles
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Summary:Airborne imaging differential optical absorption spectroscopy (DOAS), ground-based stationary DOAS, and car DOAS measurements were conducted during the S5P-VAL-DE-Ruhr campaign in September 2020. The campaign area is located in the Rhine-Ruhr region of North Rhine-Westphalia, western Germany, which is a pollution hotspot in Europe comprising urban and large industrial sources. The DOAS measurements are used to validate spaceborne NO2 tropospheric vertical column density (VCD) data products from the Sentinel-5 Precursor (S5P) TROPOspheric Monitoring Instrument (TROPOMI).Seven flights were performed with the airborne imaging DOAS instrument for measurements of atmospheric pollution (AirMAP), providing measurements that were used to create continuous maps of NO2 in the layer below the aircraft. These flights cover many S5P ground pixels within an area of 30 km × 35 km and were accompanied by ground-based stationary measurements and three mobile car DOAS instruments. Stationary measurements were conducted by two Pandora, two Zenith-DOAS, and two MAX-DOAS instruments. Ground-based stationary and car DOAS measurements are used to evaluate the AirMAP tropospheric NO2 VCDs and show high Pearson correlation coefficients of 0.88 and 0.89 and slopes of 0.90 ± 0.09 and 0.89 ± 0.02 for the stationary and car DOAS, respectively.Having a spatial resolution of about 100 m × 30 m, the AirMAP tropospheric NO2 VCD data create a link between the ground-based and the TROPOMI measurements with a nadir resolution of 3.5 km × 5.5 km and are therefore well suited to validate the TROPOMI tropospheric NO2 VCD. The observations on the 7 flight days show strong NO2 variability, which is dependent on the three target areas, the day of the week, and the meteorological conditions.The AirMAP campaign data set is compared to the TROPOMI NO2 operational offline (OFFL) V01.03.02 data product, the reprocessed NO2 data using the V02.03.01 of the official level-2 processor provided by the Product Algorithm Laboratory (PAL), and several scientific TROPOMI NO2 data products. The AirMAP and TROPOMI OFFL V01.03.02 data are highly correlated (r=0.87) but show an underestimation of the TROPOMI data with a slope of 0.38 ± 0.02 and a median relative difference of -9 %. With the modifications in the NO2 retrieval implemented in the PAL V02.03.01 product, the slope and median relative difference increased to 0.83 ± 0.06 and +20 %. However, the modifications resulted in larger scatter and the correlation
ISSN:1867-1381
1867-8548
DOI:10.5194/amt-16-1357-2023