Preprints
https://doi.org/10.5194/egusphere-2025-4421
https://doi.org/10.5194/egusphere-2025-4421
06 Oct 2025
 | 06 Oct 2025
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Unveiling the organic contribution to the initial particle growth in 3–10 nm size range

Kewei Zhang, Zhengning Xu, Fei Zhang, and Zhibin Wang

Abstract. Organic compounds play an important role in driving atmospheric particle formation and initial growth along with sulfuric acid. However, the detailed chemical composition of newly formed particles remains limited due to analytical challenges. In this study, we conducted the laboratory experiments using a flow tube reactor to investigate the roles of sulfuric acid (SA) and oxygenated organic molecules (OOMs, from α-pinene oxidation) in nanoparticle growth. For the first time, the size-resolved hygroscopicity parameter (κ) and organic mass fraction (forg) of 3–10 nm particles were measured using a custom-built scanning flow condensation particle counter (SFCPC). The hygroscopicity of SA decreased 49 % as particle size increased (from 0.413 ± 0.011 at 3 nm to 0.209 ± 0.004 at 10 nm) and declined by up to 18 % with increasing RH, primarily due to hydration effects. In contrast, the κ values of OOMs increased with RH by as much as 57 %, attributable to changes in oxidation product. Size-resolved forg revealed that larger particles contained a greater proportion of organics, indicating that SA dominates the growth of small particles, whereas OOMs contribute more significantly to growth at larger sizes. Moreover, elevated humidity enhanced the organic contribution to particle growth by up to 81 %. This enhancement was more pronounced for 5–10 nm particles due to the incorporation of increased yields of more volatile oxidation products and Kelvin effect. These valuable information on hygroscopicity and chemical composition of 3–10 nm particles during new particle formation and subsequent growth could further the understanding of related atmospheric mechanisms.

Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Kewei Zhang, Zhengning Xu, Fei Zhang, and Zhibin Wang

Status: open (until 17 Nov 2025)

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Kewei Zhang, Zhengning Xu, Fei Zhang, and Zhibin Wang
Kewei Zhang, Zhengning Xu, Fei Zhang, and Zhibin Wang

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Short summary
This study investigates how organics contribute to initial particle growth in the 3–10 nm size range. Through laboratory experiments, it was found that sulfuric acid dominates the growth of smaller particles, while organics play an increasingly important role as particle size increases. Elevated humidity also significantly enhances the contribution of organics. These findings further our understanding of new particle formation and subsequent growth.
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