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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Nov 2019

Submitted as: research article | 25 Nov 2019

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

Understanding and improving model representation of aerosol optical properties for a Chinese haze event measured during KORUS-AQ

Pablo E. Saide1,2, Meng Gao3, Zifeng Lu4, Dan Goldberg4, David G. Streets4, Jung-Hun Woo5, Andreas Beyersdorf6, Chelsea A. Corr7, Kenneth L. Thornhill8, Bruce Anderson8, Johnathan W. Hair8, Amin R. Nehrir8, Glenn S. Diskin8, Jose L. Jimenez9, Benjamin A. Nault9, Pedro Campuzano-Jost9, Jack Dibb10, Eric Heim10, Kara D. Lamb11, Joshua P. Schwarz11, Anne E. Perring12, Jhoon Kim13, Myungje Choi13,14, Brent Holben15, Gabriele Pfister16, Alma Hodzic16, Gregory R. Carmichael17, Louisa Emmons16, and James H. Crawford8 Pablo E. Saide et al.
  • 1Department of Atmospheric and Oceanic Sciences, University of California – Los Angeles, Los Angeles, CA, USA
  • 2Institute of the Environment and Sustainability, University of California –Los Angeles, Los Angeles, CA, USA
  • 3Department of Geography, Hong Kong Baptist University, Hong Kong SAR, China
  • 4Energy Systems Division, Argonne National Laboratory, Argonne, IL 60439, USA
  • 5Department of Technology Fusion Engineering, Konkuk University, Seoul, South Korea
  • 6Department of Chemistry & Biochemistry, California State University San Bernardino, San Bernardino, CA, USA
  • 7USDA UV-B Monitoring and Research Program, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, USA
  • 8NASA Langley Research Center, Hampton, VA, USA
  • 9Department of Chemistry, and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 10Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, USA
  • 11Earth System Research Laboratory, NOAA, Boulder, CO, USA
  • 12Department of Chemistry, Colgate University, Hamilton, NY, USA
  • 13Department of Atmospheric Sciences, Yonsei University, Seoul, 120-749, Korea
  • 14NASA Jet Propulsion Laboratory, Pasadena, California, USA
  • 15NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 16Atmospheric Chemistry Observations and Modeling Lab, National Center for Atmospheric Research, Boulder, CO, USA
  • 17Center for Global & Regional Environmental Research, University of Iowa, Iowa City, Iowa, USA

Abstract. KORUS-AQ was an international cooperative air quality field study in South Korea that measured local and remote sources of air pollution affecting the Korean peninsula during May–June 2016. Some of the largest aerosol mass concentrations were measured during a Chinese haze transport event (May 24th). Air quality forecasts using the WRF-Chem model with aerosol optical depth (AOD) data assimilation captured AOD during this pollution episode but over-predicted surface particulate matter concentrations, especially PM2.5 often by a factor of 2 or larger. Analysis revealed multiple sources of model deficiency related to the calculation of optical properties from aerosol mass that explain these discrepancies. Using in-situ observations of aerosol size and composition as inputs to the optical properties calculations showed that using a low resolution size bin representation under-estimates the efficiency at which aerosols scatter and absorb light (mass extinction efficiency). Besides using finer-resolution size bins, it was also necessary to increase the refractive indices and hygroscopicity of select aerosol species within the range of values reported in the literature to achieve consistency with measured values of mass/volume extinction efficiencies and light scattering enhancement factor (f(RH)) due to aerosol hygroscopic growth. Furthermore, evaluation of optical properties obtained using modeled aerosol properties revealed the inability of sectional and modal aerosol representations in WRF-Chem to properly reproduce the observed size distribution, with the models displaying a much wider accumulation mode. Other model deficiencies included an under-estimate of organic aerosol density and an over-prediction of the fractional contribution of inorganic aerosols other than sulfate, ammonium, nitrate, chloride and sodium (mostly dust). These results illustrate the complexity of achieving an accurate model representation of optical properties and provide potential solutions that are relevant to multiple disciplines and applications such as air quality forecasts, health-effect assessments, climate projections, solar-power forecasts, and aerosol data assimilation.

Pablo E. Saide et al.
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Short summary
Air quality forecasts over the Korean peninsula captured aerosol optical depth but largely over-predicted surface PM during a Chinese haze transport event. Model deficiency was related to the calculation of optical properties. In order to improve it, aerosol size representation need to be refined in the calculations and representation of aerosol properties such as size distribution, chemical composition, refractive index, hygroscopicity parameter, and density needs to be improved.
Air quality forecasts over the Korean peninsula captured aerosol optical depth but largely...