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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-847
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
10 Oct 2017
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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 2: Variability and characteristic differences under near-pristine, biomass burning, and long-range transport conditions
Mira L. Pöhlker1, Florian Ditas1, Jorge Saturno1, Thomas Klimach1, Isabella Hrabě de Angelis1, Alessandro Araùjo2, Joel Brito3,a, Samara Carbone3,b, Yafang Cheng1, Xuguang Chi1,c, Reiner Ditz1, Sachin S. Gunthe4, Konrad Kandler5, Jürgen Kesselmeier1, Tobias Könemann1, Jošt V. Lavrič6, Scot T. Martin7,8, Eugene Mikhailov9, Daniel Moran-Zuloaga1, Luciana V. Rizzo10, Diana Rose11, Hang Su1, Ryan Thalman12,d, David Walter1, Jian Wang12, Stefan Wolff1, Henrique M. J. Barbosa3, Paulo Artaxo2, Meinrat O. Andreae1,13, Ulrich Pöschl1, and Christopher Pöhlker1 1Multiphase Chemistry and Biogeochemistry Departments, Max Planck Institute for Chemistry, 55020 Mainz, Germany
2Instituto Nacional de Pesquisas da Amazonia (INPA), Manaus-AM, CEP 69083-000, Brazil
3Institute of Physics, University of São Paulo, São Paulo 05508-900, Brazil
4EWRE Division, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai 600036, India
5Institut für Angewandte Geowissenschaften, Technische Universität Darmstadt, Germany
6Department of Biogeochemical Systems, Max Planck Institute for Biogeochemistry, 07701 Jena, Germany
7John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
8Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
9St. Petersburg State University, 7/9 Universitetskaya nab, St. Petersburg, 199034, Russia
10Instituto de Ciências Ambientais, Químicas e Farmacêuticas, Universidade Federal de São Paulo (UNIFESP), Diadema, SP, Brazil
11Institut für Atmosphäre und Umwelt, Goethe Universität, 60438 Frankfurt, Germany
12Biological, Environmental & Climate Sciences Department, Brookhaven National Laboratory, Upton, NY 11973-5000, USA
13Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037, USA
anow at: Laboratoire de Météorologie Physique, Université Clermont Auvergne, Aubière, France
bnow at: Institute of Agrarian Sciences, Federal University of Uberlândia, Uberlândia, Minas Gerais, Brazil
cnow at: Institute for Climate and Global Change Research & School of Atmospheric Sciences, Nanjing University, Nanjing, 210093, China
dnow at: Department of Chemistry, Snow College, Richfield, UT, USA
Abstract. Size-resolved measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in the central Amazon Basin over a full seasonal cycle (Mar 2014–Feb 2015). In a companion part 1 paper, we presented an in-depth CCN characterization based on annually as well as seasonally averaged time intervals and discuss different parametrization strategies to represent the Amazonian CCN cycling in modelling studies (M. Pöhlker et al., 2016b). The present part 2 study analyzes the aerosol and CCN variability in original time resolution and, thus, resolves aerosol advection and transformation for the following case studies, which represent the most characteristic states of the Amazonian atmosphere:

1. Near-pristine (NP) conditions, defined as the absence of detectable black carbon (< 0.01 µg m−3), showed their highest occurrence (up to 30 %) in the wet season (i.e., Mar–May). On average, the NP episodes are characterized by a bimodal aerosol size distribution (strong Aitken mode: DAit = 70 nm, NAit = ~ 200 cm−3 vs. weaker accumulation mode: Dacc = 170 nm, Nacc = ~ 60 cm−3), a mostly organic particle composition, and relatively low hygroscopicity levels (κAit = 0.12 vs. κacc = 0.18). The NP CCN efficiency spectrum shows that the CCN population is sensitive to changes in supersaturation (S) over a wide S range.
2. Long-range transport (LRT) conditions frequently mix Saharan dust, African combustion smoke, and sea spray aerosols into the Amazonian wet season atmosphere. The LRT episodes (i.e., Feb–Apr) are characterized by an accumulation mode dominated size distribution (DAit = 80 nm, NAit = 120 cm−3 vs. Dacc = 180 nm, Nacc = 300 cm−3), a clearly increased abundance of dust and salt compounds, and relatively high hygroscopicity levels (κAit = 0.18, κacc = 0.34). The LRT CCN efficiency spectrum shows that the CCN population is highly sensitive to changes in S in the low S regime.
3. Biomass burning (BB) conditions dominate the Amazonian dry season. A selected characteristic BB episode shows a very strong accumulation mode (DAit = 70 nm, NAit = ~ 140 cm−3 vs. Dacc = 170 nm, Nacc = ~ 3400 cm−3), particles with very high organic fractions (> 90 %), and correspondingly low hygroscopicity levels (κAit = 0.14, κacc = 0.17). The BB CCN efficiency spectrum shows that the CCN population is highly sensitive to changes in S in the low S regime.
4. Mixed pollution conditions show the superposition of African (i.e., volcanic) and Amazonian (i.e., biomass burning) aerosol emissions during the dry season. The African aerosols showed a broad monomodal distribution (D = 130 nm, N = ~ 1300 cm−3), with very high sulfate fractions (20 %), and correspondingly high hygroscopicity (κAit = 0.14, κacc = 0.22). This was superimposed by fresh smoke from nearby fires with one strong mode (D = 113 nm, Nacc = ~ 2800 cm−3), an organic-dominated aerosol, and sharply decreased hygroscopicity (κAit = 0.10, κacc = 0.20). These conditions underline the rapidly changing pollution regimes with clear impacts on the aerosol and CCN properties.

Overall, this study provides detailed insights into the CCN cycling in relation to aerosol-cloud interaction in the vulnerable and climate-relevant Amazon region. The detailed analysis of aerosol and CCN key properties and particularly the extracted CCN efficiency spectra with the associated fit parameters provide a basis for an in-depth analysis of aerosol-cloud interaction in the Amazon and beyond.


Citation: Pöhlker, M. L., Ditas, F., Saturno, J., Klimach, T., Hrabě de Angelis, I., Araùjo, A., Brito, J., Carbone, S., Cheng, Y., Chi, X., Ditz, R., Gunthe, S. S., Kandler, K., Kesselmeier, J., Könemann, T., Lavrič, J. V., Martin, S. T., Mikhailov, E., Moran-Zuloaga, D., Rizzo, L. V., Rose, D., Su, H., Thalman, R., Walter, D., Wang, J., Wolff, S., Barbosa, H. M. J., Artaxo, P., Andreae, M. O., Pöschl, U., and Pöhlker, C.: Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 2: Variability and characteristic differences under near-pristine, biomass burning, and long-range transport conditions, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-847, in review, 2017.
Mira L. Pöhlker et al.
Mira L. Pöhlker et al.
Mira L. Pöhlker et al.

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Short summary
This paper presents the aerosol and CCN variability for characteristic atmospheric states, such as near-pristine conditions, African long-range transport, and biomass burning pollution, in the vulnerable and climate-relevant Amazon Basin. It summarizes the aerosol and CCN key properties and, thus, provide a basis for an in-depth analysis of aerosol-cloud interaction in the Amazon region and beyond.
This paper presents the aerosol and CCN variability for characteristic atmospheric states, such...
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