06 Dec 2022
06 Dec 2022

Tropospheric NO2 vertical profiles over South Korea and their relation to oxidant chemistry: Implications for geostationary satellite retrievals and the observation of NO2 diurnal variation from space

Laura Hyesung Yang1, Daniel J. Jacob1,2, Nadia K. Colombi2, Shixian Zhai1, Kelvin H. Bates1,3, Viral Shah4,5, Ellie Beaudry1, Robert M. Yantosca1, Haipeng Lin1, Jared F. Brewer6, Heesung Chong7, Katherine R. Travis8, James H. Crawford8, Lok Lamsal9,10, Ja-Ho Koo11, and Jhoon Kim11 Laura Hyesung Yang et al.
  • 1Harvard University, John A. Paulson School of Engineering and Applied Sciences, Cambridge, MA 02138, USA
  • 2Harvard University, Department of Earth and Planetary Sciences, Cambridge, MA 01238, USA
  • 3University of California Davis, Department of Environmental Toxicology, Davis CA 95616, USA
  • 4Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 5Science Systems and Applications, Inc., Lanham, MD 20706, USA
  • 6University of Minnesota, Department of Soil, Water and Climate, St. Paul, Minnesota, USA
  • 7Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA
  • 8NASA Langley Research Center, Hampton, VA 23666, USA
  • 9Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 10University of Maryland Baltimore County, Baltimore, MD 21250, USA
  • 11Yonsei University, Department of Atmospheric Sciences, Seoul, South Korea

Abstract. Tropospheric nitrogen dioxide (NO2) is of central importance for air quality, climate forcing, and nitrogen deposition to ecosystems. The Geostationary Environment Monitoring Spectrometer (GEMS) is now providing high-density NO2 satellite data including diurnal variation over East Asia. The NO2 retrieval requires independent vertical profile information from a chemical transport model (CTM) to compute the air mass factor (AMF) that relates the NO2 column along the line of sight to the NO2 vertical column. Here, we use aircraft observations from the Korea-United States Air Quality (KORUS-AQ) campaign over the Seoul Metropolitan Area (SMA) and around the Korean peninsula to better understand the factors controlling the NO2 vertical profile, its diurnal variation, the implications for the AMF, and the ability of the GEOS-Chem CTM to compute the AMF and its variability. Proper representation of oxidant chemistry is critical for the CTM simulation of NO2 vertical profiles and is achieved in GEOS-Chem through new model developments including aerosol nitrate photolysis, reduced uptake of hydroperoxy (HO2) radicals by aerosols, and accounting for atmospheric oxidation of volatile chemical products (VCPs). We find that the tropospheric NO2 columns measured from space are mainly contributed by the planetary boundary layer (PBL) below 2 km altitude, reflecting the highly polluted conditions. Repeated measurements of NO2 vertical profiles over SMA at different times of day show that diurnal change in mixing depth affecting the NO2 vertical profile induces a diurnal variation in AMF of comparable magnitude to the diurnal variation in the NO2 column. GEOS-Chem captures this diurnal variation in AMF and more generally the variability in the AMF for the KORUS-AQ NO2 vertical profiles (2.7 % mean bias, 7.6 % precision), with some outliers in the morning due to non-systematic errors in the timing of mixed layer growth.

Laura Hyesung Yang et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-1309', Anonymous Referee #1, 20 Dec 2022
  • RC2: 'Comment on egusphere-2022-1309', Anonymous Referee #2, 04 Jan 2023
  • RC3: 'Comment on egusphere-2022-1309', Anonymous Referee #3, 12 Jan 2023

Laura Hyesung Yang et al.

Laura Hyesung Yang et al.


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Short summary
A geostationary satellite can now provide hourly NO2 columns and obtaining the NO2 columns from space relies on NO2 vertical distribution from the chemical transport model (CTM). In this work, we update the CTM to better represent the chemistry environment so that the CTM can accurately provide NO2 vertical distribution. Then we find that the changes in NO2 vertical distribution and the length of the light path over the course of the day play important roles in the NO2 column’s hourly variation.