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Discussion papers
https://doi.org/10.5194/acp-2018-1336
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-1336
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Feb 2019

Research article | 05 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Retrieval of total column and surface NO2 from Pandora zenith-sky measurements

Xiaoyi Zhao1, Debora Griffin1, Vitali Fioletov1, Chris McLinden1, Jonathan Davies1, Akira Ogyu1, Sum Chi Lee1, Alexandru Lupu1, Michael D. Moran1, Alexander Cede2,3, Martin Tiefengraber3,4, and Moritz Müller3,4 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
  • 4Department of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria

Abstract. Pandora spectrometers can retrieve nitrogen dioxide (NO2) vertical column densities (VCDs) via two viewing geometries: direct-sun and zenith-sky. The direct-sun NO2 VCD measurements have high quality (0.1 DU accuracy in clear-sky conditions) and do not rely on any radiative transfer model to calculate air mass factors (AMFs); however, they are not available when the sun is obscured by clouds. To perform NO2 measurements in cloudy conditions, a simple but robust NO2 retrieval algorithm is developed for Pandora zenith-sky measurements. This algorithm derives empirical zenith-sky NO2 AMFs from coincident high-quality direct-sun NO2 observations. Moreover, the retrieved Pandora zenith-sky NO2 VCD data are converted to surface NO2 concentrations with a scaling algorithm that uses chemical-transport-model predictions and satellite measurements as inputs. NO2 VCDs and surface concentrations are retrieved from Pandora zenith-sky measurements made in Toronto, Canada, from 2015 to 2017. The retrieved Pandora zenith-sky NO2 data (VCD and surface concentration) show good agreement with both satellite and in situ measurements. The diurnal and seasonal variations of derived Pandora zenith-sky surface NO2 data also agree well with in situ measurements (diurnal difference within ±2 ppbv). Overall, this work shows that the new Pandora zenith-sky NO2 products have the potential to be used in various applications such as future satellite validation in moderate cloudy scenes and air quality monitoring.

Xiaoyi Zhao et al.
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Xiaoyi Zhao et al.
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Short summary
New nitrogen dioxide (NO2) retrieval algorithm are developed for Pandora zenith-sky measurements. A column-to-surface conversion look-up table was produced for the Pandora instruments; therefore, quick and practical Pandora-based surface NO2 concentration data can be obtained for air quality monitoring purposes. It is demonstrated that the surface NO2 concentration is controlled not only by the planetary boundary-layer height, but also by both boundary-layer dynamics and photochemistry.
New nitrogen dioxide (NO2) retrieval algorithm are developed for Pandora zenith-sky...
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