Maho Nakagawa1,2, Tomoki Nakayama This email address is being protected from spambots. You need JavaScript enabled to view it.1,3, Hiroshi Sasago1, Yuki Kuruma1,4, Hikari Yai5, Shuhei Ogawa5, Yange Deng5,6, Michihiro Mochida1,5, Yutaka Matsumi1

1 Institute for Space-Earth Environmental Research, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
2 National Institute of Information and Communications Technology, Koganei, Tokyo 184-8795, Japan
3 Faculty of Environmental Science and Graduate School of Fisheries and Environmental Sciences, Nagasaki University, Bunkyo-machi, Nagasaki 852-8521, Japan
4 National Institute of Advanced Industrial Science and Technology, Umezono, Tsukuba 305-8560, Japan
5 Graduate School of Environmental Studies, Nagoya University, Chikusa-ku, Nagoya 464-8601, Japan
6 National Institute for Environmental Studies, Tsukuba 305-8506, Japan


Received: January 16, 2020
Revised: July 3, 2020
Accepted: July 5, 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.

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Nakagawa, M., Nakayama, T., Sasago, H., Kuruma, Y., Yai, H., Ogawa, S., Deng, Y., Mochida, M. and Matsumi, Y. (2020). Assessment of the Sphericity of Submicrometer Particles Using a Single-particle Polar Nephelometer at an Urban Site in Japan. Aerosol Air Qual. Res.


  • Scattering angular distribution of individual particles was measured in an urban site.
  • Particle sphericity was estimated from scattering angular distribution.
  • At least two types of particles with high and low sphericities were externally mixed.
  • Particle sphericity increased during daytime by photochemical formation or aging.
  • Nitrate formation possibly increased sphericity in the early morning during high RH.


The sphericity of particles must be considered when evaluating their effects on the climate and human health. Thus, to examine this property and its controlling factors, this study measured the scattering angular distributions of both thermodenuded and non-thermodenuded individual particles with a diameter of 500 nm in real time using a home-made polar nephelometer in Nagoya, Japan. Estimating the sphericities based on the depths of the local minima in the scattering angular distributions, we found the ambient aerosols to be external mixtures of at least two types of particles, one with relatively high and the other with relatively low sphericity. Although most of the particles exhibiting high sphericity were removed as they passed through the thermodenuder, approximately one-third of the fraction exhibiting low sphericity remained. During the daytime, the proportion of the low-sphericity particles decreased, whereas the average sphericity of the high-sphericity particles increased, which can be attributed to photochemical formation and/or aging processes. On days with extremely high relative humidity, the diurnal variation in the average sphericity displayed another peak during the early morning, which may have been due to the secondary formation of nitrate.

Keywords: Polar nephelometer; Scattering angular distribution; Single particle; Particle sphericity.

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