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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/amt-2019-416
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2019-416
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 13 Dec 2019

Submitted as: research article | 13 Dec 2019

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This preprint is currently under review for the journal AMT.

Assessment of the quality of TROPOMI high-spatial-resolution NO2 data products

Xiaoyi Zhao1, Debora Griffin1, Vitali Fioletov1, Chris McLinden1, Alexander Cede2,3, Martin Tiefengraber3,4, Moritz Müller3,4, Kristof Bognar5, Kimberly Strong5, Folkert Boersma6,7, Henk Eskes6, Jonathan Davies1, Akira Ogyu1, and Sum Chi Lee1 Xiaoyi Zhao et al.
  • 1Air Quality Research Division, Environment and Climate Change Canada, Toronto, M3H 5T4, Canada
  • 2NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 3LuftBlick, Kreith 39A, 6162 Mutter, Austria
  • 4Departmentof Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria
  • 5Department of Physics, University of Toronto, Toronto, ON, M5S 1A7, Canada
  • 6Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands
  • 7Environmental Sciences Group, Wageningen University, Wageningen, the Netherlands

Abstract. The TROPOspheric Monitoring Instrument (TROPOMI) on-board the Sentinel-5 Precursor satellite (launched on 13 October 2017) is a nadir-viewing spectrometer measuring reflected sunlight in the ultraviolet, visible, near-infrared, and shortwave infrared spectral ranges. The measured spectra are used to retrieve total columns of trace gases, including nitrogen dioxide (NO2). For ground validation of these satellite measurements, Pandora spectrometers, which retrieve high-quality NO2 total columns via direct-sun measurements, are widely used. In this study, Pandora NO2 measurements made at three sites located in or north of the Greater Toronto Area (GTA) are used to evaluate the TROPOMI NO2 data products, including standard Royal Netherlands Meteorological Institute (KNMI) tropospheric and stratospheric NO2 data product and a TROPOMI research data product developed by Environment and Climate Change Canada (ECCC) using a high-resolution regional air quality forecast model (used in the air mass factor calculation). It is found that these current TROPOMI tropospheric NO2 data products (standard and ECCC) met the TROPOMI design bias requirement. Using the statistical uncertainty estimation method, the estimated TROPOMI upper limit precision falls below the design requirement at a rural site, but above in the other two urban and suburban sites. The Pandora instruments are found to have sufficient precision to perform TROPOMI validation work. In addition to the traditional satellite validation method (i.e., pairing ground-based measurements with satellite measurements closest in time and space), we analyzed TROPOMI pixels located upwind and downwind from the Pandora site. This makes it possible to improve the statistics and better interpret the high-spatial-resolution measurements made by TROPOMI. By using this wind-based validation technique, the number of coincident measurements can be increased by about a factor of five. Using this larger number of coincident measurements, this work shows that both TROPOMI and Pandora instruments can reveal detailed spatial patterns (i.e., horizontal distributions) of local and transported NO2 emissions, which can be used to evaluate regional air quality changes. The TROPOMI ECCC NO2 research data product shows improved agreement with Pandora measurements compared to the TROPOMI standard tropospheric NO2 data product, demonstrating benefits from the high-resolution regional air quality forecast model.

Xiaoyi Zhao 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

Xiaoyi Zhao et al.

Xiaoyi Zhao et al.

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Short summary
Pandora NO2 measurements made at three sites located in Toronto area are used to evaluate the TROPOspheric Monitoring Instrument (TROPOMI) NO2 data products, including standard NO2 data and research data developed using a high-resolution regional air quality forecast model. TROPOMI pixels located upwind and downwind from the Pandora sites were analyzed by a new wind-based validation method, which revealed the spatial patterns of local and transported emissions and regional air quality changes.
Pandora NO2 measurements made at three sites located in Toronto area are used to evaluate the...
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