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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2018-55
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
31 Jan 2018
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Multi-year statistical and modelling analysis of submicrometer aerosol number size distributions at a rain forest site in Amazonia
Luciana Varanda Rizzo1, Pontus Roldin2, Joel Brito3,a, John Backman4,b, Erik Swietlicki2, Radovan Krejci5, Peter Tunved5, Tukka Petäjä4, Markku Kulmala4, and Paulo Artaxo3 1Departamento de Ciências Ambientais, Universidade Federal de São Paulo, Diadema, Brazil
2Physics Institute, Lund University, Lund, Sweden
3Instituto de Física, Universidade de São Paulo, São Paulo, Brazil
4Department of Physics, University of Helsinki, Helsinki, Finland
5Department of Environmental Science and Analytical Chemistry (ACES), Stockholm University, Stockholm, Sweden
anow at: Laboratory for Meteorological Physics, Université Clermont Auvergne, Clermont-Ferrand, France
bnow at: Finnish Meteorological Institute, Atmospheric Composition Research, Helsinki, Finland
Abstract. The Amazon Basin is a unique region to study atmospheric aerosols, given their relevance for the regional hydrological cycle and large uncertainty of their sources. Multi-year datasets are crucial when contrasting periods of natural conditions and periods influenced by anthropogenic emissions. In the wet season, biogenic sources and processes prevail, and the Amazonian atmospheric composition resembles pre-industrial conditions. In the dry season, the Basin is influenced by widespread biomass burning emissions. This work reports multi-year observations of high time resolution submicrometer (10–600 nm) particle number size distributions at a rain forest site in Amazonia (TT34 tower, 60 km NW from Manaus city), between years 2008–2010 and 2012–2014. Median particle number concentration was 403 cm−3 in the wet season and 1254 cm−3 in the dry season. The Aitken mode (~ 30–100 nm in diameter) was prominent during the wet season, while accumulation mode (~ 100–600 nm in diameter) dominated the particle size spectra during the dry season. Cluster analysis identified groups of aerosol number size distribution influenced by convective downdrafts, nucleation events and fresh biomass burning emissions. New particle formation and subsequent growth was rarely observed during the 749 days of observations, similar to previous observations in the Amazon Basin. A stationary 1D column model (ADCHEM – Aerosol Dynamics, gas and particle phase CHEMistry and radiative transfer model) was used to assess importance of processes behind the observed diurnal particle size distribution trends. Three major particle source types are required in the model to reproduce the observations: (i) a surface source of particles in the evening, possibly related to primary biological emissions (ii) entrainment of accumulation mode aerosols in the morning, and (iii) convective downdrafts transporting Aitken mode particles into the boundary layer mostly during the afternoon. The latter process has the largest influence on the modelled particle number size distributions. However, convective downdrafts are often associated with rain and thus act both as a source of Aitken mode particles, and as a sink of accumulation mode particles, causing a net reduction in the median total particle number concentrations in the surface layer. Our study shows that the combination of the three mentioned particle sources are essential to sustain particle number concentrations in Amazonia.

Citation: Rizzo, L. V., Roldin, P., Brito, J., Backman, J., Swietlicki, E., Krejci, R., Tunved, P., Petäjä, T., Kulmala, M., and Artaxo, P.: Multi-year statistical and modelling analysis of submicrometer aerosol number size distributions at a rain forest site in Amazonia, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2018-55, in review, 2018.
Luciana Varanda Rizzo et al.
Luciana Varanda Rizzo et al.
Luciana Varanda Rizzo et al.

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Short summary
Aerosols are tiny particles suspended in the air, much smaller than a strand of hair. They are naturally emitted in the Amazon forest. They interact with sunlight and form clouds, affecting the climate. They also recycle nutrients for the forest. We described how aerosols transform along the hours, days and seasons in Amazonia. We found that part of the aerosols are naturally emitted at the surface, and part come from above, brought down by intense air movements related to tropical clouds.
Aerosols are tiny particles suspended in the air, much smaller than a strand of hair. They are...
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