Aerosol and ozone vertical distribution and fluxes over the Amazonian boundary layer

Atmospheric aerosols in the Amazon forest exhibit strong temporal variability driven by seasonally changing sources and boundary-layer processes [1]. In central Amazonia, wet-season conditions are typically dominated by biogenic emissions and secondary organic aerosol (SOA) formation, whereas dry-season conditions are strongly influenced by biomass-burning emissions and long-range transport events [2]. This variability makes the region a natural laboratory for investigating aerosol–boundary layer interactions and vertical exchange processes.

The occurrence of convection, turbulence, and boundary-layer dynamics promotes the vertical motion of particles and trace gases [3]. These processes govern the exchange of particles between atmospheric layers, allowing surface-emitted aerosols to reach the free troposphere through deep convection, while SOA formed at higher levels may be reintroduced into the boundary layer through subsidence and downdrafts. Convective downdrafts associated with precipitation have also been shown to increase ground-level ozone concentration, contributing to new particle formation and growth [4].

In this context, this study aims to evaluate particle and ozone fluxes over the central Amazon, quantifying the importance of vertical transport mechanisms for the atmospheric composition within the lower troposphere. A diverse range of ground-based measurements performed at the 325-m Amazon Tall Tower Observatory (ATTO) was employed, combining long-term aerosol observations, sonic anemometer measurements, and a novel robotic lift system [5] that enables continuous vertical profiling of aerosol properties.

Both eddy covariance and flux-gradient techniques were employed to derive vertical fluxes of particles and ozone during clean wet season conditions. The gradient-based analysis reveals coherent vertical flux patterns associated with rainfall intensity, boundary-layer stratification, and diurnal evolution. Deposition aerosol fluxes dominated, with a mean value of −0.28(12) × 10⁶ m⁻² s⁻¹, in agreement with other flux studies conducted in the Amazon region [6]. Furthermore, negative ozone fluxes were also consistently observed during strong precipitation, indicating the downward transport of ozone-rich air from upper levels in these events.

This study sheds light on the magnitude and importance of multiple vertical transport mechanisms, including emission, dry and wet deposition, downdrafts, and the diurnal evolution of the boundary layer, for the variability of aerosol concentrations in the Amazon. Our results provide quantitative constraints on sources, sinks, and transformation pathways of aerosol particles, contributing to an improved understanding of aerosol–turbulence interactions in tropical forest environments and their implications for the local climate.

 

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

[2] R. Valiati, et al. Atmos. Chem. Phys. 25.21 (2025): 14923–14944.

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

[4] L. A. T. Machado, et al. Nat. Geosci. 17 (2024): 1225–1232.

[5] S. Brill, et al. Atmos. Meas. Tech. 19.1 (2026): 101–118.

[6] L. Ahlm, et al. Atmos. Chem. Phys. 9.24 (2009): 9381–9400.