Comparison of Phase States of PM2.5over Megacities, Seoul and Beijing, and Their Implications on Particle Size Distribution

Mijung Song, Rani Jeong, Daeun Kim, Yanting Qiu, Xiangxinyue Meng, Zhijun Wu, Andreas Zuend, Yoonkyeong Ha, Changhyuk Kim, Haeri Kim, Sanjit Gaikwad, Kyoung Soon Jang, Ji Yi Lee, Joonyoung Ahn

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


Although the particle phase state is an important property, there is scant information on it, especially, for real-world aerosols. To explore the phase state of fine mode aerosols (PM2.5) in two megacities, Seoul and Beijing, we collected PM2.5filter samples daily from Dec 2020 to Jan 2021. Using optical microscopy combined with the poke-and-flow technique, the phase states of the bulk of PM2.5as a function of relative humidity (RH) were determined and compared to the ambient RH ranges in the two cities. PM2.5was found to be liquid to semisolid in Seoul but mostly semisolid to solid in Beijing. The liquid state was dominant on polluted days, while a semisolid state was dominant on clean days in Seoul. These findings can be explained by the aerosol liquid water content related to the chemical compositions of the aerosols at ambient RH; the water content of PM2.5was much higher in Seoul than in Beijing. Furthermore, the overall phase states of PM2.5observed in Seoul and Beijing were interrelated with the particle size distribution. The results of this study aid in a better understanding of the fundamental physical properties of aerosols and in examining how these are linked to PM2.5in polluted urban atmospheres.

Original languageEnglish
Pages (from-to)17581-17590
Number of pages10
JournalEnvironmental Science and Technology
Issue number24
StatePublished - 20 Dec 2022

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  • PM
  • aerosol liquid water content
  • megacities
  • morphology
  • phase state
  • size distribution


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