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

14 April 2026

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, the authors 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.

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.

Contact: Paulo Artaxo (artaxo@if.usp.br)