Hyung-Min Lee1†, Se Pyo Lee2†, Yugen Li3, Jian Zhen Yu3, Jin Young Kim4, Yong Pyo Kim5, Ji Yi Lee This email address is being protected from spambots. You need JavaScript enabled to view it.6 

1 School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea
2 Environmental Meteorology Research Division, National Institute of Meteorological Sciences, Seogwipo, Korea
3 Division of Environment and Sustainability, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
4 Green City Technology Institute, Korea Institute of Science and Technology, Seoul, Korea
5 Department of Chemical Engineering and Materials Science, Ewha Womans University, Seoul, Korea
6 Department of Environ. Sci. and Engineering, Ewha Womans University, Seoul, Korea

These authors contributed equally to this work

Received: May 16, 2020
Revised: September 26, 2020
Accepted: October 1, 2020

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Download Citation: ||https://doi.org/10.4209/aaqr.2020.05.0233  

Cite this article:

Lee, H.M., Lee, S.P., Li, Y., Yu, J.Z., Kim, J.Y., Kim, Y.P., Lee, J.Y. (2021). Characterization of Seasonal Difference of HULIS-C Sources from Water Soluble PM2.5 in Seoul, Korea: Probing Secondary Processes. Aerosol Air Qual. Res. 21, 200233. https://doi.org/10.4209/aaqr.2020.05.0233


  • A year-long observation of HULIS-C were made in Seoul, Korea in Oct 2012–Sep 2013.
  • Seasonal variation of concentrations and sources were investigated.
  • HULIS-C concentration shows winter maximum and summer minimum.
  • Aging and heterogeneous reaction contribute to year-round background.
  • Fresh biomass burning and incomplete combustion are sources of seasonal variation.


HUmic-LIke Substances (HULIS) consists of a significant fraction of water-soluble organic carbon (WSOC) and optically active brown carbon. Understanding seasonality in their abundance and sources is an important step to quantifying their impacts on air quality and climate. In this study, we characterized the seasonal variation of HULIS-C (the carbon component of HULIS) and identified primary and secondary sources contributing to HULIS-C at an urban site in Seoul, Korea by analyzing 131 PM2.5 samples collected over a year from October 2012 to September 2013. The HULIS-C in Seoul had an annual average of 2.0 µg m3, and displayed a seasonality of highest abundance in the winter (2.7 ± 1.3 µg m3) and the lowest in the summer (1.7 ± 0.8 µg m3). Its fraction in WSOC reached up to 0.96 in the summer while remained relatively constant in the range of 0.4–0.6 in other seasons. Sources of HULIS-C were resolved using Positive Matrix Factorization (PMF) and checked using inter-species relationships between HILIS-C and aerosol components. Specifically, secondary processes including aging and heterogeneous reaction (26%) contributes to the year-round background concentration of HULIS-C and fresh biomass burning (38%) and incomplete combustion (16%) were the major sources of underlying seasonal variation. We also found aging process in the secondary process had an important role in HULIS-C formation and was a dominant contributor in the summer while heterogenous reaction contributed considerably in other seasons. It implies that the different secondary processes in forming HULIS should be considered when the radiative forcing of brown carbon is estimated. Because these processes can lead the different physicochemical properties of HULIS in aerosols.

Keywords: Seasonal variation, Aging, Heterogeneous reaction, Positive matrix factorization

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