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Volume 18, issue 17 | Copyright

Special issue: Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5)...

Atmos. Chem. Phys., 18, 13245-13264, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 14 Sep 2018

Research article | 14 Sep 2018

Ground-based observation of clusters and nucleation-mode particles in the Amazon

Daniela Wimmer1, Stephany Buenrostro Mazon1, Hanna Elina Manninen1,2, Juha Kangasluoma1, Alessandro Franchin1,3,4, Tuomo Nieminen1,5, John Backman6, Jian Wang7, Chongai Kuang7, Radovan Krejci8, Joel Brito9,10, Fernando Goncalves Morais9, Scot Turnbull Martin11, Paulo Artaxo9, Markku Kulmala1, Veli-Matti Kerminen1, and Tuukka Petäjä1 Daniela Wimmer et al.
  • 1Department of Physics, University of Helsinki, Gustaf Hallströmin katu 2a, 00560, Helsinki, Finland
  • 2European Organization for Nuclear Research (CERN), 1211 Geneva, Switzerland
  • 3NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, CO, USA
  • 4Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA
  • 5Department of Applied Physics, University of Eastern Finland, P.O. Box 1627, 70211 Kuopio, Finland
  • 6Finnish Meteorological Institute, Atmospheric composition research, Erik Palménin aukio 1, 00560, Helsinki, Finland
  • 7Environmental and Climate Sciences Department, Brookhaven National Laboratory, Upton, NY, USA
  • 8Stockholm University, Department of Environmental Science and Analytical Chemistry (ACES), 106 91 Stockholm, Sweden
  • 9Institute of Physics, University of São Paulo, de Fisica, Universidade de Sao Paulo, Rua do Matao 1371, CEP 05508-090, Sao Paulo, Brazil
  • 10Laboratory for Meteorological Physics (LaMP), Université Clermont Auvergne, 63000 Clermont-Ferrand, France
  • 11School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

Abstract. We investigated atmospheric new particle formation (NPF) in the Amazon rainforest using direct measurement methods. To our knowledge this is the first direct observation of NPF events in the Amazon region. However, previous observations elsewhere in Brazil showed the occurrence of nucleation-mode particles. Our measurements covered two field sites and both the wet and dry season. We measured the variability of air ion concentrations (0.8–12nm) with an ion spectrometer between September 2011 and January 2014 at a rainforest site (T0t). Between February and October 2014, the same measurements were performed at a grassland pasture site (T3) as part of the GoAmazon 2014/5 experiment, with two intensive operating periods (IOP1 and IOP2 during the wet and the dry season, respectively). The GoAmazon 2014/5 experiment was designed to study the influence of anthropogenic emissions on the changing climate in the Amazon region. The experiment included basic aerosol and trace gas measurements at the ground, remote sensing instrumentation, and two aircraft-based measurements.

The results presented in this work are from measurements performed at ground level at both sites. The site inside the rainforest (T0t) is located 60km NNW of Manaus and influenced by pollution about once per week. The pasture (T3) site is located 70km downwind from Manaus and influenced by the Manaus pollution plume typically once per day or every second day, especially in the afternoon. No NPF events were observed inside the rainforest (site T0t) at ground level during the measurement period. However, rain-induced ion and particle bursts (hereafter, rain events) occurred frequently (643 of 1031 days) at both sites during the wet and dry season, being most frequent during the wet season. During the rain events, the ion concentrations in three size ranges (0.8–2, 2–4, and 4–12nm) increased up to about 104–105cm−3. This effect was most pronounced in the intermediate and large size ranges, for which the background ion concentrations were about 10–15cm−3 compared with 700cm−3 for the cluster ion background.

We observed eight NPF events at the pasture site during the wet season. We calculated the growth rates and formation rates of neutral particles and ions for the size ranges 2–3 and 3–7nm using the ion spectrometer data. The observed median growth rates were 0.8 and 1.6nmh−1 for 2–3nm sized ions and particles, respectively, with larger growth rates (13.3 and 7.9nmh−1) in the 3–7nm size range. The measured nucleation rates were of the order of 0.2cm−3s−1 for particles and 4–9×10−3cm−3s−1 for ions. There was no clear difference in the sulfuric acid concentrations between the NPF event days and nonevent days ( ∼ 9×105cm−3). The two major differences between the NPF days and nonevent days were a factor of 1.8 lower condensation sink on NPF event days (1.8×10−3s−1) compared to nonevents (3.2×10−3s−1) and different air mass origins.

To our knowledge, this is the first time that results from ground-based sub-3nm aerosol particle measurements have been obtained from the Amazon rainforest.

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This work focuses on understanding the production of very small airborne particles in the undisturbed environment of the Amazon basin. Computer models have shown that up to 70 % of these tiny particles are responsible for cloud formation on a global scale. The processes behind the production of these very small particles have been studied intensely recently. Their appearance has been observed almost all over the world. We directly measure sub-3 nm aerosols for the first time in the Amazon basin.
This work focuses on understanding the production of very small airborne particles in the...