Title: Long-term observations of cloud condensation nuclei over the Amazon rain forest - Part 2: Variability and characteristics of biomass burning, long-range transport, and pristine rain forest aerosols

Abstract

For this study, size-resolved measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted over a full seasonal cycle at the remote Amazon Tall Tower Observatory (ATTO, March 2014–February 2015). In a preceding companion paper, we presented annually and seasonally averaged data and parametrizations (Part 1; Pöhlker et al., 2016a). In the present study (Part 2), we analyze key features and implications of aerosol and CCN properties for the following characteristic atmospheric conditions: Empirically pristine rain forest (PR) conditions, where no influence of pollution was detectable, as observed during parts of the wet season from March to May. The PR episodes are characterized by a bimodal aerosol size distribution (strong Aitken mode with D_Ait ≈ 70nm and N_Ait ≈ 160cm^-3, weak accumulation mode with D_acc ≈ 160nm and N_acc ≈ 90cm^-3), a chemical composition dominated by organic compounds, and relatively low particle hygroscopicity (κ_Ait ≈ 0.12, κ_acc ≈ 0.18). Long-range-transport (LRT) events, which frequently bring Saharan dust, African biomass smoke, and sea spray aerosols into the Amazon Basin, mostly during February to April. The LRT episodes are characterized by a dominant accumulation mode (_DAit ≈ 80nm, N_Ait ≈ 120cm^-3 vs. D_acc ≈ 180nm, N_acc ≈ 310cm^-3),more » an increased abundance of dust and salt, and relatively high hygroscopicity (κ_Ait ≈ 0.18, κ_acc ≈ 0.35). The coarse mode is also significantly enhanced during these events. Biomass burning (BB) conditions characteristic for the Amazonian dry season from August to November. The BB episodes show a very strong accumulation mode (D_Ait ≈ 70nm, N_Ait ≈ 140cm^-3 vs. D_acc ≈ 170nm, N_acc ≈ 3400cm^-3), very high organic mass fractions (~90%), and correspondingly low hygroscopicity (κ_Ait ≈ 0.14, κ_acc ≈ 0.17). Mixed-pollution (MPOL) conditions with a superposition of African and Amazonian aerosol emissions during the dry season. During the MPOL episode presented here as a case study, we observed African aerosols with a broad monomodal distribution (D ≈ 130nm, N_{CN, 10} ≈ 1300cm^-3), with high sulfate mass fractions (~20%) from volcanic sources and correspondingly high hygroscopicity (κ _{< 100 nm} ≈ 0.14, κ _{> 10 nm} ≈ 0.22), which were periodically mixed with fresh smoke from nearby fires (D ≈ 110nm, N_{CN, 10} ≈ 2800cm^-3) with an organic-dominated composition and sharply decreased hygroscopicity (κ _{< 150 nm} ≈ 0.10, κ _{> 150 nm} ≈ 0.20). Insights into the aerosol mixing state are provided by particle hygroscopicity (κ) distribution plots, which indicate largely internal mixing for the PR aerosols (narrow κ distribution) and more external mixing for the BB, LRT, and MPOL aerosols (broad κ distributions). The CCN spectra (CCN concentration plotted against water vapor supersaturation) obtained for the different case studies indicate distinctly different regimes of cloud formation and microphysics depending on aerosol properties and meteorological conditions. The measurement results suggest that CCN activation and droplet formation in convective clouds are mostly aerosol-limited under PR and LRT conditions and updraft-limited under BB and MPOL conditions. Normalized CCN efficiency spectra (CCN divided by aerosol number concentration plotted against water vapor supersaturation) and corresponding parameterizations (Gaussian error function fits) provide a basis for further analysis and model studies of aerosol–cloud interactions in the Amazon.« less

Authors:

Pöhlker, Mira L. ^[1]; Ditas, Florian ^[1]; Saturno, Jorge  ^[2];

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Klimach, Thomas ^[1]; Hrabě de Angelis, Isabella  ^[1];

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Araùjo, Alessandro C. ^[3]; Brito, Joel  ^[4];

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Carbone, Samara ^[5]; Cheng, Yafang  ^[1];

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Chi, Xuguang ^[6]; Ditz, Reiner ^[1]; Gunthe, Sachin S. ^[7]; Holanda, Bruna A. ^[1]; Kandler, Konrad ^[8]; Kesselmeier, Jürgen  ^[1];

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Könemann, Tobias  ^[1];

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Krüger, Ovid O. ^[1]; Lavrič, Jošt V.  ^[9];

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Martin, Scot T. ^[10]; Mikhailov, Eugene  ^[11]

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more »; Moran-Zuloaga, Daniel ^[1]; Rizzo, Luciana V. ^[12]; Rose, Diana ^[13]; Su, Hang  ^[1];

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Thalman, Ryan ^[14]; Walter, David  ^[1];

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Wang, Jian  ^[15];

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Wolff, Stefan ^[1]; Barbosa, Henrique M. J. ^[16]; Artaxo, Paulo  ^[3];

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Andreae, Meinrat O.  ^[17];

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Pöschl, Ulrich  ^[1];

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Pöhlker, Christopher ^[1] « less

---

+ Show Author Affiliations

1. Max Planck Inst. for Chemistry, Mainz (Germany). Multiphase Chemistry and Biogeochemistry Dept.
2. Max Planck Inst. for Chemistry, Mainz (Germany). Multiphase Chemistry and Biogeochemistry Dept.; Braunschweig Univ. of Technology (Germany)
3. Brazilian Agricultural Research Corp. (EMBRAPA), Belem (Brazil)
4. Univ. of Sao Paulo (Brazil). Inst. of Physics; Univ. of Clermont Auvergne, Aubière (France). Physical Meterorology Lab.
5. Univ. of Sao Paulo (Brazil). Inst. of Physics; Federal Univ. of Uberlandia (Brazil). Inst. of Agrarian Sciences
6. Max Planck Inst. for Chemistry, Mainz (Germany). Multiphase Chemistry and Biogeochemistry Dept.; Nanjing Univ. (China). Inst. for Climate and Global Change Research and School of Atmospheric Sciences
7. Indian Inst. of Technology (IIT), Madras (India). Environmental and Water Resources Engineering (EWRE) Division and Dept. of Civil Engineering
8. Technical Univ. of Darmstadt (Germany). Inst. of Applied Geosciences
9. Max Planck Inst. for Biogeochemistry, Jena (Germany). Dept. of Biogeochemical Systems
10. Harvard Univ., Cambridge, MA (United States). John A. Paulson School of Engineering and Applied Sciences and Dept. of Earth and Planetary Sciences
11. St. Petersburg State Univ. (Russian Federation)
12. Federal Univ. of Sao Paulo (UNIFESP) (Brazil). Inst. of Environmental, Chemical and Pharmaceutical Sciences
13. Goethe Univ., Frankfurt (Germany). Inst. of Atmospheric and Environmental Sciences; Hessian Agency for Nature Conservation, Environment and Geology (HLNUG), Wiesbaden (Germany)
14. Brookhaven National Lab. (BNL), Upton, NY (United States). Biological, Environmental & Climate Sciences Dept.; Snow College, Richfield, UT (United States). Dept. of Chemistry
15. Brookhaven National Lab. (BNL), Upton, NY (United States). Biological, Environmental & Climate Sciences Dept.
16. Univ. of Sao Paulo (Brazil). Inst. of Physics
17. Max Planck Inst. for Chemistry, Mainz (Germany). Multiphase Chemistry and Biogeochemistry Dept.; Univ. of California, San Diego, CA (United States). Scripps Inst. of Oceanography

Publication Date:

Thu Jul 19 00:00:00 EDT 2018

Research Org.:

Brookhaven National Laboratory (BNL), Upton, NY (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); Max Planck Society; German Federal Ministry of Education and Research (BMBF); Ministry of Science, Technology, Innovation and Communication (MCTIC) (Brazil); Amazon State Univ. (UEA), Manaus (Brazil); Amazonas State Research Support Foundation (FAPEAM) (Brazil); National Inst. of Amazonian Research (INPA). Large Scale Biosphere-Atmosphere Program in Amazonia (LBA); German Research Foundation (DFG); European Union (EU); Sao Paulo Research Foundation (FAPESP); Russian Science Federation (RSF); National Aeronautics and Space Administration (NASA)

OSTI Identifier:

1466979

Report Number(s):

BNL-208012-2018-JAAM
Journal ID: ISSN 1680-7324

Grant/Contract Number:  

SC0012704; 01LB1001A; 01.11.01248.00; KA 2280/2; 11.37.220.2016; 603445; 13/05014-0; 13/50510-5; 18-17- 00076

Resource Type:

Journal Article: Accepted Manuscript

Journal Name:

Atmospheric Chemistry and Physics (Online)

Additional Journal Information:

Journal Volume: 18; Journal Issue: 14; Journal ID: ISSN 1680-7324

Publisher:

European Geosciences Union

Country of Publication:

United States

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES