Wetting properties of fresh urban soot particles: Evaluation based on critical supersaturation and observation of surface trace materials

Sayako Ueda; Tatsuhiro Mori; Yoko Iwamoto; Yuta Ushikubo; Kazuhiko Miura

doi:10.1016/j.scitotenv.2021.152274

Wetting properties of fresh urban soot particles: Evaluation based on critical supersaturation and observation of surface trace materials

Sci Total Environ. 2022 Mar 10:811:152274. doi: 10.1016/j.scitotenv.2021.152274. Epub 2021 Dec 10.

Authors

Sayako Ueda¹, Tatsuhiro Mori², Yoko Iwamoto³, Yuta Ushikubo², Kazuhiko Miura⁴

Affiliations

¹ Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan. Electronic address: ueda.sayako@d.mbox.nagoya-u.ac.jp.
² Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan; Department of Physics, Faculty of Science Division I, Tokyo University of Science, Tokyo 162-8601, Japan.
³ Graduate School of Integrated Sciences for Life, Hiroshima University, 1-7-1, Kagamiyama, Higashi, Hiroshima 739-8521, Japan.
⁴ Department of Physics, Faculty of Science Division I, Tokyo University of Science, Tokyo 162-8601, Japan; Laboratory for Environmental Research at Mount Fuji, 2-5-5 Okubo, Shinjuku-ku, Tokyo 169-0072, Japan.

PMID: 34902417
DOI: 10.1016/j.scitotenv.2021.152274

Abstract

Soot particles strongly absorb solar radiation and contribute to global warming. Also, wetting properties of soot at emission can affect its lifetime. We investigated surface conditions related to wetting and hydrophobic properties of fresh soot using data from measurements taken in Tokyo. A cloud condensation nuclei (CCN) counter was used to clarify surface conditions of particles composed mainly of water-insoluble (WI) materials: total and active particles as CCN around critical supersaturation (S_c) of 203-nm-diameter WI particles. Averaged number fractions of inactivated particles as CCN at 1.05% supersaturation (SS), which is S_c of hydrophilic WI particles, were estimated as 1.4%. Number fractions of inactive particles changed less at 1.78%SS during rush hour and increased at 0.89%SS, implying that most of the WI particles included small amounts of water-soluble (WS) materials rather than being completely hydrophobic. Based on transmission electron microscope (TEM) analysis of samples collected during rush hour, 69% of the mostly bare soot particles had Na or K small domains that are regarded as originating in fossil fuels. Based on water dialysis analysis results, some Na and K on soot were WS. Combination results with CCN measurements suggest that these WS materials decrease the S_c of soot. Moreover, the morphological structure of sulfate covering Na and K domains on the soot surface implicates pre-existing sodium and potassium compounds on soot as a trigger of soot aging. However, inactive particles at S_c at poor-hydrophilic particles and soot particles composed solely of WI materials on TEM samples were also found, although they were minor. Such particles, which are unfavorable for obtaining a wettable surface, might retain non-hygroscopicity for a longer period in the atmosphere. Evaluation of long-range soot transport can benefit from consideration of slight and inhomogeneous differences of chemical compounds on soot that occur along with their emission.

Keywords: Atmospheric aerosols; Black carbon; Contact angle; Microscopic analysis; Particle morphology.

MeSH terms

Aerosols / analysis
Atmosphere / analysis
Particle Size
Renal Dialysis*
Soot*

Substances

Aerosols
Soot