ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-11997-2012 Size distributions and temporal variations of biological aerosol particles in the Amazon rainforest characterized by microscopy and real-time UV-APS fluorescence techniques during AMAZE-08 Huffman J. A. 1 2 Sinha B. 3 4 Garland R. M. 2 7 Snee-Pollmann A. 3 8 Gunthe S. S. 2 9 Artaxo P. 5 Martin S. T. 6 Andreae M. O. 2 Pöschl U. 2 University of Denver, Department of Chemistry and Biochemistry, Denver, CO, USA Max Planck Institute for Chemistry, Biogeochemistry Department, Mainz, Germany Max Planck Institute for Chemistry, Particle Chemistry Department, Mainz, Germany IISER Mohali, Department of Earth Sciences, S. A. S. Nagar, Manauli PO, India Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo, Brazil Harvard University, School of Engineering and Applied Sciences & Department of Earth and Planetary Sciences, Cambridge, MA, USA now at: Council for Scientific and Industrial Research (CSIR), Natural Resources and the Environment, Pretoria, South Africa now at: Roche Diagnostics GmbH, Pharma Research and Early Development, Penzberg, Germany now at: Indian Institute for Technology Madras, Department of Civil Engineering & EWRE Division, Chennai-36, India 18 12 2012 12 24 11997 12019 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/11997/2012/acp-12-11997-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/11997/2012/acp-12-11997-2012.pdf

As a part of the AMAZE-08 campaign during the wet season in the rainforest of central Amazonia, an ultraviolet aerodynamic particle sizer (UV-APS) was operated for continuous measurements of fluorescent biological aerosol particles (FBAP). In the coarse particle size range (> 1 μm) the campaign median and quartiles of FBAP number and mass concentration were 7.3 &times; 10<sup>4</sup> m<sup>−3</sup> (4.0–13.2 &times; 10<sup>4</sup> m<sup>−3</sup>) and 0.72 μg m<sup>−3</sup> (0.42–1.19 μg m<sup>−3</sup>), respectively, accounting for 24% (11–41%) of total particle number and 47% (25–65%) of total particle mass. During the five-week campaign in February–March 2008 the concentration of coarse-mode Saharan dust particles was highly variable. In contrast, FBAP concentrations remained fairly constant over the course of weeks and had a consistent daily pattern, peaking several hours before sunrise, suggesting observed FBAP was dominated by nocturnal spore emission. This conclusion was supported by the consistent FBAP number size distribution peaking at 2.3 μm, also attributed to fungal spores and mixed biological particles by scanning electron microscopy (SEM), light microscopy and biochemical staining. A second primary biological aerosol particle (PBAP) mode between 0.5 and 1.0 μm was also observed by SEM, but exhibited little fluorescence and no true fungal staining. This mode may have consisted of single bacterial cells, brochosomes, various fragments of biological material, and small Chromalveolata (Chromista) spores. Particles liquid-coated with mixed organic-inorganic material constituted a large fraction of observations, and these coatings contained salts likely from primary biological origin. We provide key support for the suggestion that real-time laser-induce fluorescence (LIF) techniques using 355 nm excitation provide size-resolved concentrations of FBAP as a lower limit for the atmospheric abundance of biological particles in a pristine environment. We also show some limitations of using the instrument for ambient monitoring of weakly fluorescent particles < 2 μm. Our measurements confirm that primary biological particles, fungal spores in particular, are an important fraction of supermicron aerosol in the Amazon and that may contribute significantly to hydrological cycling, especially when coated by mixed inorganic material.

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