Document Type

Article

Publication Date

2018

Publication Title

Atmospheric Chemistry and Physics

ISSN

1680-7324

Volume

18

Issue

24

DOI

http://dx.doi.org/10.5194/acp-18-17769-2018

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 Yellow Sea coupled to FLEXPART Lagrangian simulations. During KORUS-AQ, the average OA loading advected into Seoul was ∼1–3 µg sm−3. Second, taking this background into account, the dilution-corrected SOA concentration observed over Seoul was ∼140 µgsm-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 (20–70 µgsm-3ppmv-1 at 0.5 equivalent days). For the average OA concentration observed over Seoul (13 µg sm−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 of 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, dihydroxytoluene, 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 Yellow 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 11 % on average and suggest that short-lived hydrocarbons (i.e., xylenes, trimethylbenzenes, and semi-volatile 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.

Comments

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


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, Munich, 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


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Creative Commons Attribution 4.0 License
This work is licensed under a Creative Commons Attribution 4.0 License.

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