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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 24 Aug 2018

Research article | 24 Aug 2018

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

Secondary Organic Aerosol Production from Local Emissions Dominates the Organic Aerosol Budget over Seoul, South Korea, during KORUS-AQ

Benjamin A. Nault1,2, Pedro Campuzano-Jost1,2, Douglas A. Day1,2, Jason C. Schroder1,2, Bruce Anderson3, Andreas J. Beyersdorf3,a, Donald R. Blake4, William H. Brune5, Yonghoon Choi3,6, Chelsea A. Corr3,b, Joost A. de Gouw1,2, Jack Dibb7, Joshua P. DiGangi3, Glenn S. Diskin3, Alan Fried8, L. Gregory Huey9, Michelle J. Kim10, Christoph J. Knote11, Kara D. Lamb2,12, Taehyoung Lee13, Taehyun Park13, Sally E. Pusede14, Eric Scheuer7, Kenneth L. Thornhill3,6, Jung-Hun Woo15, and Jose L. Jimenez1,2 Benjamin A. Nault et al.
  • 1Department of Chemistry, University of Colorado, Boulder, CO, USA
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 3NASA Langley Research Center, Hampton, Virginia, USA
  • 4Department of Chemistry, University of California, Irvine, Irvine, CA, USA
  • 5Department of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, Pennsylvania, USA
  • 6Science Systems and Applications, Inc., Hampton, Virginia, USA
  • 7Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, USA
  • 8Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA
  • 9School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
  • 10Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  • 11Meteorologisches Institut, Ludwig-Maximilians-Universität München, München, Germany
  • 12Chemical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 13Department of Environmental Science, Hankuk University of Foreign Studies, Republic of Korea
  • 14Department of Environmental Sciences, University of Virginia, Charlottesville, VA, USA
  • 15Department of Advanced Technology Fusion, Konkuk University, Seoul, Republic of Korea
  • anow at: Department of Chemistry and Biochemistry, California State University, San Bernardino, California
  • bnow at: USDA UV-B Monitoring and Research Program, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, USA

Abstract. Organic aerosol (OA) is an important fraction of submicron aerosols. However, it is challenging to predict and attribute the specific organic compounds and sources that lead to observed OA loadings, largely due to contributions from secondary production. This is especially true for megacities surrounded by numerous regional sources that create an OA background. Here, we utilize in-situ gas and aerosol observations collected on-board the NASA DC-8 during the NASA/NIER KORUS-AQ (KORea United States-Air Quality) campaign to investigate the sources and hydrocarbon precursors that led to the secondary OA (SOA) production observed over Seoul. First, we investigate the contribution of transported OA to total loadings observed over Seoul, by using observations over the West Sea coupled to FLEXPART Lagrangian simulations. During KORUS-AQ, the average OA loading advected into Seoul was ~1–3µgsm−3. Second, taking this background into account, the dilution-corrected SOA concentration observed over Seoul was ~140µgsm−3ppmv−1 at 0.5 equivalent photochemical days. This value is at the high end of what has been observed in other megacities around the world (20–70µgsm−3ppmv−1 at 0.5 equivalent days). For the average OA concentration observed over Seoul (13µgsm−3), it is clear that production of SOA from locally emitted precursors is the major source in the region. The importance of local SOA production was supported by the following observations: (1) FLEXPART source contribution calculations indicate any hydrocarbons with a lifetime less than 1 day, which are shown to dominate the observed SOA production, mainly originate from South Korea. (2) SOA correlated strongly with other secondary photochemical species, including short-lived species (formaldehyde, peroxy acetyl nitrate, sum of acyl peroxy nitrates, dihydroxy toluene, and nitrate aerosol). (3) Results from an airborne oxidation flow reactor (OFR), flown for the first time, show a factor of 4.5 increase in potential SOA concentrations over Seoul versus over the West Sea, a region where background air masses that are advected into Seoul can be measured. (4) Box model simulations reproduce SOA observed over Seoul within 15% on average, and suggest that short-lived hydrocarbons (i.e., xylenes, trimethylbenzenes, semi- and intermediate volatility compounds) were the main SOA precursors over Seoul. Toluene, alone, contributes 9% of the modeled SOA over Seoul. Finally, along with these results, we use the metric ΔOA/ΔCO2 to examine the amount of OA produced per fuel consumed in a megacity, which shows less variability across the world than ΔOA/ΔCO.

Benjamin A. Nault et al.
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Status: final response (author comments only)
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Benjamin A. Nault et al.
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Short summary
Aerosol impact visibility and human health in large cities. Sources of the aerosols are still highly uncertain, especially for cities surrounded by numerous other cities. We use observations collected during the Korean-United States Air Quality study to determine the sources of organic aerosol. We find that organic aerosol is rapidly produced over Seoul, South Korea, and that the sources of the organic aerosol originates from short-lived hydrocarbons, which originate from local emissions.
Aerosol impact visibility and human health in large cities. Sources of the aerosols are still...