New particle formation in the Amazonian atmosphere and the role of organic compounds

Tropical forests are essential ecosystems for the global aerosol population [1]. The mechanisms behind new particle formation (NPF) in the Amazon have long remained elusive, with traditional “banana” events being rarely observed. Recent studies show that forest emissions of volatile organic compounds (VOCs) that are subsequently oxidized produce particles that can serve as Cloud Condensation Nuclei (CCN), which are critical for the tropical hydrological cycle. Several studies showed that new particle formation can occur at high altitudes (12-14 Km) [2]. Nanoparticles are also produced by different mechanisms at the canopy level, following oxidation by VOCs and downdrafts [3]. Another study showed that Quiet New Particle Formation also occurs in Amazonia and can be responsible for a significant fraction of the aerosol population [4]. These studies show a wide diversity of processes that produce nanoparticles, which adds to the population of primary biological particle emissions [1]. Ground-based long-term measurements were conducted at the Amazon Tall Tower Experiment (ATTO), integrating over 10 years of wet-season size-distribution measurements. Intensive aircraft campaigns conducted during the CAFÉ-Brazil experiment have identified the mechanisms underlying high-altitude particle production. We have also studied the role that deep convection and strong precipitation events play in modulating the particle population at the forest canopy level.

Of particular interest is the strong interaction between the plant metabolism and the climate they control, since aerosol particles influence the radiation balance, carbon cycling, and precipitation patterns. These natural wet-season processes compete with the dry-season biomass burning emissions, which strongly alter the particle population.

In this presentation, we will discuss the complex picture of particle production and development in Amazonia. This study sheds light on a previously unknown process of nucleation and growth occurring frequently in the Amazonian BL, distinct from the known intense particle bursts and growth associated with downdrafts.

[1] P. Artaxo, et al. Tellus Series B 24.1 (2022): 24–163.

[2] J. Curtius et al., Nature, 636 (2024) 124–130.

[3] L. A. T. Machado, et al., Atmos. Chem. Phys., 21.23 (2021) 18065–18086.

[4] B. B. Meller, et al., EGUsphere, 2025-4581 (2025).