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Discussion papers
https://doi.org/10.5194/acp-2018-678
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2018-678
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Jul 2018

Research article | 13 Jul 2018

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

A top-down assessment using OMI NO2 suggests an underestimate in the NOx emissions inventory in Seoul, South Korea during KORUS-AQ

Daniel L. Goldberg1,2, Pablo E. Saide3, Lok N. Lamsal4,5, Benjamin de Foy6, Zifeng Lu1,2, Jung-Hun Woo7, Younha Kim7, Jinseok Kim7, Meng Gao8, Gregory Carmichael9, and David G. Streets1,2 Daniel L. Goldberg et al.
  • 1Energy Systems Division, Argonne National Laboratory, Argonne, IL 60439 USA
  • 2Consortium for Advanced Science and Engineering, University of Chicago, Chicago, IL 60637, USA
  • 3Department of Atmospheric and Oceanic Sciences, Institute of the Environment and Sustainability, University of California – Los Angeles, Los Angeles, CA 90095, USA
  • 4Goddard Earth Sciences Technology and Research, Universities Space Research Association, Columbia, MD 21046, USA
  • 5NASA Goddard Space Flight Center, Code 614, Greenbelt, MD 20771, USA
  • 6Department of Earth and Atmospheric Sciences, Saint Louis University, Saint Louis, MO 63108, USA
  • 7Konkuk University, 05029 Seoul, South Korea
  • 8School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
  • 9Department of Chemical and Biochemical Engineering, University of Iowa, Iowa City, IA 52242, USA

Abstract. In this work, we investigate the NOx emissions inventory in Seoul, South Korea using a regional NASA Ozone Monitoring Instrument (OMI) NO2 product. We first develop a regional OMI NO2 product by re-calculating the air mass factors using a high-resolution (4×4km2) WRF-Chem model simulation, which better captures the NO2 shape profiles in urban regions. We then apply a model-derived spatial averaging kernel to further downscale the retrieval and account for the sub-pixel variability. These two modifications yield OMI NO2 values in the regional product that are 1.37 larger in the Seoul metropolitan region and >2 times larger near large industrial sources. These two modifications also yield an OMI NO2 product that is in better agreement with the Pandora NO2 spectrometer measurements acquired during the Korea U.S.-Air Quality (KORUS-AQ) field campaign. NOx emissions are then derived for the Seoul metropolitan area during the KORUS-AQ field campaign using a top-down approach with the standard and regional NASA OMI NO2 products. We first apply the top-down approach to a model simulation to ensure that the method is appropriate: the WRF-Chem simulation utilizing the bottom-up emission inventory yields a NOx emission rate of 227±94kton/yr, while the bottom-up inventory itself yields a NOx emission rate of 198kton/yr. Using the top-down approach on the regional OM NO2 product, we derive the NOx emissions rate from Seoul to be 484±201kton/yr, and a 353±146kton/yr NOx emissions rate using the standard NASA OMI NO2 product. This suggests an underestimate of 53% and 36% using the regional and standard NASA OMI NO2 products respectively. To supplement this finding, we compare the NO2 simulated by WRF-Chem to observations of the same quantity acquired by aircraft and find a model underestimate. When NOx emissions in the WRF-Chem model are doubled, there is better agreement with KORUS-AQ aircraft observations. Although the current work is focused on South Korea using OMI, the methodology developed in this work can be applied to other world regions using TROPOMI and future satellite datasets (e.g., GEMS and TEMPO) to produce high-quality region-specific top-down NOx emission estimates.

Daniel L. Goldberg et al.
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Status: final response (author comments only)
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Daniel L. Goldberg et al.
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Short summary
Using satellite data, we are able to estimate the emissions of NOx (NOx=NO+NO2), a toxic group of air pollutants, in the Seoul metropolitan area. We first develop an enhanced satellite product that better observes NO2 in urban regions. Using this new product, we derive NOx emission estimates to be nearly twice as large as the emissions reported by the Korean government. The implications are that the measures taken to reduce NOx emissions have not been as effective as regulators have thought.
Using satellite data, we are able to estimate the emissions of NOx (NOx=NO+NO2), a toxic group...
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