Assessment of the quality of tropomi high-spatial-resolution no2 data products in the greater toronto area

Xiaoyi Zhao*, Debora Griffin, Vitali Fioletov, Chris McLinden, Alexander Cede, Martin Tiefengraber, Moritz Müller, Kristof Bognar, Kimberly Strong, Folkert Boersma, Henk Eskes, Jonathan Davies, Akira Ogyu, Sum Chi Lee

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

12 Citations (Scopus)

Abstract

The TROPOspheric Monitoring Instrument (TROPOMI) aboard 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 (<span classCombining double low line"inline-formula">NO2</span>). For ground validation of these satellite measurements, Pandora spectrometers, which retrieve high-quality <span classCombining double low line"inline-formula">NO2</span> total columns via direct-sun measurements, are widely used. In this study, Pandora <span classCombining double low line"inline-formula">NO2</span> measurements made at three sites located in or north of the Greater Toronto Area (GTA) are used to evaluate the TROPOMI <span classCombining double low line"inline-formula">NO2</span> data products, including a standard Royal Netherlands Meteorological Institute (KNMI) tropospheric and stratospheric <span classCombining double low line"inline-formula">NO2</span> 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 (in the air mass factor calculation). It is found that these current TROPOMI tropospheric <span classCombining double low line"inline-formula">NO2</span> data products (standard and ECCC) met the TROPOMI design bias requirement (&lt;&thinsp;10&thinsp;%). 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 (&lt;&thinsp;0.02&thinsp;DU) 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 5. With 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 <span classCombining double low line"inline-formula">NO2</span> emissions, which can be used to evaluate regional air quality changes. The TROPOMI ECCC <span classCombining double low line"inline-formula">NO2</span> research data product shows improved agreement with Pandora measurements compared to the TROPOMI standard tropospheric <span classCombining double low line"inline-formula">NO2</span> data product (e.g., lower multiplicative bias at the suburban and urban sites by about 10&thinsp;%), demonstrating benefits from the high-resolution regional air quality forecast model.

Original languageEnglish
Article number13
Pages (from-to)2131-2159
Number of pages29
JournalAtmospheric Measurement Techniques
Volume13
Issue number4
DOIs
Publication statusPublished - 30 Apr 2020

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