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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  25 May 2020

25 May 2020

Review status
A revised version of this preprint is currently under review for the journal AMT.

Evaluating Sentinel-5P TROPOMI tropospheric NO2 column densities with airborne and Pandora spectrometers near New York City and Long Island Sound

Laura M. Judd1, Jassim A. Al-Saadi1, James J. Szykman2, Lukas C. Valin2, Scott J. Janz3, Matthew G. Kowalewski3,4, Henk J. Eskes5, J. Pepijn Veefkind5,6, Alexander Cede7, Moritz Mueller7, Manuel Gebetsberger7, Robert Swap3, R. Bradley Pierce8, Caroline R. Nowlan9, Gonzalo González Abad9, Amin Nehrir1, and David Williams2 Laura M. Judd et al.
  • 1NASA Langley Research Center, Hampton, VA, 23681, United States
  • 2United States Environmental Protection Agency Office of Research and Development, Triangle Research Park, NC, 27709, United States
  • 3NASA Goddard Space Flight Center, Greenbelt, MD, 20771, United States
  • 4Universities Space Research Association, Columbia, MD, 21046, United States
  • 5Royal Netherlands Meteorological Institute (KNMI), De Bilt, Netherlands
  • 6Delft University of Technology, Department of Geoscience and Remote Sensing, Delft, Netherlands
  • 7LuftBlick, Kreith, Austria
  • 8University of Wisconsin-Madison Space Science and Engineering Center, Madison, WI, 53706, United States
  • 9Harvard-Smithsonian Center for Astrophysics Cambridge, MA, 02138

Abstract. Abundant NO2 column measurements from airborne and ground-based Pandora spectrometers were collected as part of the 2018 Long Island Sound Tropospheric Ozone Study (LISTOS) in the New York City/Long Island Sound region and coincided with early measurements from the Sentinel-5P TROPOMI instrument. Both airborne- and ground-based measurements are used to evaluate the TROPOspheric Monitoring Instrument (TROPOMI) NO2 Tropospheric Vertical Column (TrVC) product v1.2 in this region, which has high spatial and temporal heterogeneity in NO2. First, airborne and Pandora TrVCs are compared to evaluate the uncertainty of the airborne TrVC and establish the spatial representativeness of the Pandora observations. The 171 coincidences between Pandora and airborne TrVCs are found to be highly correlated (r2=0.92 and slope of 1.03) with the biggest individual differences being associated with high temporal and/or spatial variability. These reference measurements (Pandora and airborne) are complementary with respect to temporal coverage and spatial representivity. Pandora spectrometers can provide continuous long-term measurements but may lack areal representivity when operated in direct-sun mode. Airborne spectrometers are typically only deployed for short periods of time, but their observations are more spatially representative of the satellite measurements with the added capability of retrieving at subpixel resolutions of 250 m × 250 m over the entire TROPOMI pixels they overfly. Thus, airborne data are more correlated with TROPOMI measurements (r2=0.96) than Pandora measurements are with TROPOMI (r2=0.84). The largest outliers between TROPOMI and the reference measurements are caused by errors in the TROPOMI retrieval of cloud pressure impacting the calculation of tropospheric air mass factors in cloud-free scenes. This factor causes a high bias in TROPOMI TrVCs of 4–11 %. Excluding these cloud-impacted points, TROPOMI has an overall low bias of 19–33% during the LISTOS timeframe of June–September 2018. Part of this low bias is caused by coarse a priori profile input from TM5-MP model; replacing these profiles with those from a 12 km NAMCMAQ analysis results in a 12–14 % increase in the TrVCs. Even with this improvement, the TROPOMI-NAMCMAQ TrVCs have a 7–19 % low bias, indicating needed improvement in a priori assumptions in the air mass factor calculation. Future work should explore additional impacts of a priori inputs to further assess the remaining low biases in TROPOMI using these datasets.

Laura M. Judd et al.

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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Laura M. Judd et al.

Laura M. Judd et al.


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Latest update: 21 Sep 2020
Publications Copernicus
Short summary
This paper evaluates Sentinel-5P TROPOMI v1.2 NO2 tropospheric columns over New York City using data from airborne mapping spectrometers and a network of ground-based spectrometers (Pandora) collected in 2018. These evaluations consider impacts due to cloud parameters, a priori profile assumptions, and spatial/temporal variability. Overall, TROPOMI tropospheric NO2 columns appear to have a low bias in this region.
This paper evaluates Sentinel-5P TROPOMI v1.2 NO2 tropospheric columns over New York City using...