26 Jun 2023
 | 26 Jun 2023

Amazonian Aerosol Size Distributions in a Lognormal Phase Space: Characteristics and Trajectories

Gabriela Rosalino Unfer, Luiz Augusto Toledo Machado, Paulo Artaxo, Marco Aurelio Franco, Leslie A. Kremper, Mira L. Pöhlker, Ulrich Pöschl, and Christopher Pöhlker

Abstract. This study introduces a new approach to represent and analyse particle number size distributions (PNSD) of atmospheric aerosols. Amazonian aerosol data, measured from May 2021 to April 2022 at the Amazon Tall Tower Observatory (ATTO), were fitted by a trimodal lognormal function and the outputs were evaluated by means of the N-Dg-σ phase space. This is a 3D space defined by the three fit parameters of the lognormal function, which represents, for a given mode i, the number concentration (Ni), the geometric median diameter (Dg,i), and the geometric standard deviation (σi). Each state of a PNSD is represented by a single dot in this phase space, while a collection of dots shows the delimitation of all PNSD states under given conditions. The connections in ensembles of data points show trajectories caused by pseudo-forces, such as precipitation regimes and vertical movement. Characteristic patterns of the Amazonian PNSDs were found in the N-Dg-σ phase space, including the sub-50 nm mode appearing as a curved cone, the Aitken mode as a semi-sphere, and the accumulation mode as a cylinder. The trajectories of the data points as a function of seasonal and diel trends occur as well-defined paths. An ellipsoid pattern describes all possible seasonal states PNSDs of the accumulation mode. The diurnal cycle of sub-50 nm particles in the dry season shows a positive linear slope as a function of all three fit parameters. For wet and dry seasons, the diurnal cycle in the accumulation mode is mainly driven by changes in N. As an effect of precipitation on the PNSDs and vice-versa, N and Dg were found to increase for the sub-50 nm mode and to decrease for the Aitken and accumulation modes after the precipitation peak. While afternoons with precipitation were preceded by mornings with larger particles of the accumulation mode, whose mean geometric diameter was ~10 nm larger than in days without precipitation. Nevertheless, only in the wet season both concentration and diameter seem to influence further rainfall. Observed patterns of the PNSDs in the N-Dg-σ phase space can support the characterization of atmospheric aerosols e.g. in comparisons of different measurement sites, contribute to our understanding of the main processes in aerosol-cloud interactions, and open new perspectives on aerosol parametrizations. This study introduced a first glance of Amazonian aerosols in an N-Dg-σ phase space.

Gabriela Rosalino Unfer et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1361', Daniele Visioni, 12 Sep 2023
  • RC2: 'Comment on egusphere-2023-1361', Anonymous Referee #2, 05 Oct 2023

Gabriela Rosalino Unfer et al.

Gabriela Rosalino Unfer et al.


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Short summary
Amazonian aerosols and their interactions with precipitation were studied by proposing its understanding in a 3D space based on three parameters that characterize the concentration and size distribution of aerosols. The results showed characteristic arrangements regarding seasonal and diurnal cycles, as well as when interacting with precipitation. The use of this 3D space appears to be a promising tool for aerosol populations analysis and for model validation and parameterization.