Articles | Volume 26, issue 7
https://doi.org/10.5194/acp-26-4885-2026
https://doi.org/10.5194/acp-26-4885-2026
ACP Letters
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14 Apr 2026
ACP Letters | Highlight paper |  | 14 Apr 2026

Quiet New Particle Formation is a significant aerosol source in the Amazon boundary layer

Bruno B. Meller, Marco A. Franco, Rafael Valiati, Christopher Pöhlker, Luiz A. T. Machado, Florian Ditas, Leslie A. Kremper, Subha S. Raj, Cleo Q. Dias-Júnior, Flávio A. F. D'Oliveira, Luciana V. Rizzo, Ulrich Pöschl, and Paulo Artaxo

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Cited articles

Aliaga, D., Tuovinen, S., Zhang, T., Lampilahti, J., Li, X., Ahonen, L., Kokkonen, T., Nieminen, T., Hakala, S., Paasonen, P., Bianchi, F., Worsnop, D., Kerminen, V.-M., and Kulmala, M.: Nanoparticle ranking analysis: determining new particle formation (NPF) event occurrence and intensity based on the concentration spectrum of formed (sub-5 nm) particles, Aerosol Research, 1, 81–92, https://doi.org/10.5194/ar-1-81-2023, 2023. 
Artaxo, P., Rizzo, L. V., Brito, J. F., Barbosa, H. M. J., Arana, A., Sena, E. T., Cirino, G. G., Bastos, W., Martin, S. T., and Andreae, M. O.: Atmospheric aerosols in Amazonia and land use change: from natural biogenic to biomass burning conditions, Faraday Discuss., 165, 203–235, https://doi.org/10.1039/C3FD00052D, 2013. 
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Editorial statement
New particle formation, or nucleation, is known to be a globally important source of atmospheric aerosol particles, based on observations and model simulations. However, much of the observational evidence of its importance is based on clear nucleation "events" driven by strong photochemical processes that peak during the daytime. Here, the authors show that over Central Amazonia nearly half of the Aitken-mode sized particles with diameters 10-25 nm stem from a slower but hitherto hidden production of particles. This discovery changes our understanding of aerosol budgets in the lower atmosphere, requiring a reappraisal of measurements and model simulations for this and other regions.
Short summary
Aerosols are tiny particles that help clouds form and influence the climate. In the Amazon, clear events of new aerosol particle formation are rare, making it difficult to explain their origin. Using ten years of measurements, we discovered a subtle but frequent process called Quiet New Particle Formation. This hidden mechanism slowly produces and grows small particles and is responsible for nearly half of the smallest aerosols observed during the wet season.
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