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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.

  08 Oct 2020

08 Oct 2020

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This preprint is currently under review for the journal AMT.

New Observations of Upper Tropospheric NO2 from TROPOMI

Eloise A. Marais1,2, John F. Roberts3, Robert G. Ryan4,5, Henk Eskes6, K. Folkert Boersma6,7, Sungyeon Choi8,9, Joanna Joiner8, Nader Abuhassan8,10, Alberto Redondas11, Michel Grutter12, Alexander Cede13, Laura Gomez14,15, and Monica Navarro-Comas14 Eloise A. Marais et al.
  • 1Department of Geography, University College London, London, UK
  • 2School of Physics and Astronomy, University of Leicester, Leicester, UK
  • 3Centre for Landscape and Climate Research, University of Leicester, Leicester, UK
  • 4School of Earth Sciences, The University of Melbourne, Melbourne, Australia
  • 5ARC Centre of Excellence for Climate System Science, Sydney, Australia
  • 6Satellite Observations Department, Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands
  • 7Meteorology and Air Quality Group, Wageningen University (WUR), Wageningen, the Netherlands
  • 8NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 9Science Systems and Applications, Inc., Lanham, MD, USA
  • 10Joint Center for Earth Systems Technology, University of Maryland, Baltimore County, Baltimore, MD, USA
  • 11Izaña Atmospheric Research Center, AEMET, Tenerife, Canary Islands, Spain
  • 12Centro de Ciencias de la Atmósfera, Universidad Nacional Autónoma de México, Mexico City, Mexico
  • 13LuftBlick, Fritz-Konzert-Straße 4, Innsbruck, Austria
  • 14Instituto Nacional de Técnica Aeroespacial (INTA), Área de Investigación e Instrumentación Atmosférica, Ctra Ajalvir km4, 28850, Torrejón de Ardoz, Madrid, Spain
  • 15Groupe de Spectrométrie Moléculaire et Atmosphérique, URM CNRS 7331, UFR Sciences Exactes et Naturelles, Moulin de la Housse, BP 1039, 51687 Reims CEDEX 2, France

Abstract. Nitrogen oxides (NOx ≡ NO + NO2) in the NOx-limited upper troposphere (UT) are long-lived and so have a large influence on the oxidizing capacity of the troposphere and formation of the greenhouse gas ozone. Models misrepresent NOx in the UT and observations to address deficiencies in models are sparse. Here we obtain a year of near-global seasonal mean mixing ratios of NO2 in the UT (450–180 hPa) at 1 ° x 1° by applying cloud-slicing to partial columns of NO2 from TROPOMI. This follows refinement of the cloud-slicing algorithm with synthetic partial columns from the GEOS-Chem chemical transport model. We find that synthetic cloud-sliced UT NO2 are spatially consistent (R = 0.64) with UT NO2 calculated across the same cloud pressure range and scenes as are cloud-sliced (“true” UT NO2), but the cloud-sliced UT NO2 is 11–22 % more than the "true" all-sky seasonal mean. The largest contributors to differences between synthetic cloud-sliced and “true” UT NO2 are target resolution of the cloud-sliced product and uniformity of overlying stratospheric NO2. TROPOMI, prior to cloud-slicing, is corrected for a 13 % underestimate in stratospheric NO2 variance and a 50 % overestimate in free tropospheric NO2 determined by comparison to Pandora total columns at high-altitude sites in Mauna Loa, Izaña and Altzomoni, and MAX-DOAS and Pandora tropospheric columns at Izaña. Two cloud-sliced seasonal mean UT NO2 products for June 2019 to May 2020 are retrieved from corrected TROPOMI total columns using distinct TROPOMI cloud products that assume clouds are reflective boundaries (FRESCO-S) or water droplet layers (ROCINN-CAL). TROPOMI UT NO2 typically ranges from 20-30 pptv over remote oceans to > 80 pptv over locations with intense seasonal lightning. Spatial coverage is mostly in the tropics and subtropics with FRESCO-S and extends to the midlatitudes and polar regions with ROCINN-CAL, due to its greater abundance of optically thick clouds and wider cloud top altitude range. TROPOMI UT NO2 seasonal means are spatially consistent (R = 0.6–0.8) with an existing coarser spatial resolution (5° latitude x 8° longitude) UT NO2 product from the Ozone Monitoring Instrument (OMI). UT NO2 from TROPOMI is 12–26 pptv more than that from OMI due to increase in NO2 with altitude from the OMI pressure ceiling (280 hPa) to that for TROPOMI (180 hPa), but possibly also systematic altitude differences between the TROPOMI and OMI cloud products. The TROPOMI UT NO2 product offers potential to evaluate and improve representation of UT NOx in models and supplement aircraft observations that are sporadic and susceptible to large biases in the UT.

Eloise A. Marais et al.

Interactive discussion

Status: open (until 10 Dec 2020)
Status: open (until 10 Dec 2020)
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Eloise A. Marais et al.

Model code and software

ERC UpTrop TROPOMI UT NO2 python processing code Eloise A. Marais and John F. Roberts

Eloise A. Marais et al.


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Publications Copernicus
Short summary
Nitrogen oxides in the upper troposphere have a profound influence on the global troposphere, though observations there are exceedingly rare. We apply cloud-slicing to high spatial resolution TROPOMI total columns of nitrogen dioxide (NO2) to derive near-global observations of upper tropospheric NO2 concentrations and show consistency with existing datasets. These data offer tremendous potential to address knowledge gaps in this oft under-appreciated portion of the atmosphere.
Nitrogen oxides in the upper troposphere have a profound influence on the global troposphere,...