ACP Atmospheric Chemistry and Physics ACP Atmos. Chem. Phys. 1680-7324 Copernicus Publications Göttingen, Germany 10.5194/acp-14-8559-2014 Characterisation of bioaerosol emissions from a Colorado pine forest: results from the BEACHON-RoMBAS experiment Crawford I. https://orcid.org/0000-0003-4433-7310 1 Robinson N. H. 2 Flynn M. J. 1 Foot V. E. 3 Gallagher M. W. https://orcid.org/0000-0002-4968-6088 1 Huffman J. A. https://orcid.org/0000-0002-5363-9516 4 Stanley W. R. 5 Kaye P. H. 5 Centre for Atmospheric Science, SEAES, University of Manchester, Manchester, UK Met Office, Exeter, UK Defence Science and Technology Laboratory, Porton Down, Salisbury, SP4 0JQ, UK Department of Chemistry & Biochemistry, University of Denver, 2190 E. Illif Ave., Denver, CO, 80208, USA Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK 25 08 2014 14 16 8559 8578 Copyright: © 2014 I. Crawford et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://acp.copernicus.org/articles/14/8559/2014/acp-14-8559-2014.html The full text article is available as a PDF file from https://acp.copernicus.org/articles/14/8559/2014/acp-14-8559-2014.pdf

The behaviour of primary biological aerosols (PBAs) at an elevated, un-polluted North American forest site was studied using an ultra violet-light induced fluorescence (UV-LIF) measurement technique in conjunction with hierarchical agglomerative cluster analysis (HA-CA). Contemporaneous UV-LIF measurements were made with two wide-band integrated bioaerosol spectrometers, WIBS-3 and WIBS-4, which sampled close to the forest floor and via a continuous vertical profiling system, respectively. Additionally, meteorological parameters were recorded at various heights throughout the forest and used to estimate PBAP (Primary Biological Aerosol Particle) fluxes. HA-CA using data from the two, physically separated WIBS instruments independently yielded very similar cluster solutions. <br><br> All fluorescent clusters displayed a diurnal minimum at midday at the forest floor with maximum concentration occurring at night. Additionally, the number concentration of each fluorescent cluster was enhanced, to different degrees, during wet periods. A cluster that displayed the greatest enhancement and highest concentration during sustained wet periods appears consistent with behaviour reported for fungal spores. A cluster that appears to be behaviourally consistent with bacteria dominated during dry periods. Fluorescent particle concentrations were found to be greater within the forest canopy than at the forest floor, indicating that the canopy was the main source of these particles rather than the minimal surface vegetation, which appeared to contribute little to overall PBA concentrations at this site. <br><br> Fluorescent particle concentration was positively correlated with relative humidity (RH), and parameterisations of the aerosol response during dry and wet periods are reported. The aforementioned fungal spore-like cluster displayed a strong positive response to increasing RH. The bacteria-like cluster responded more strongly to direct rain-fall events than other PBA types. Peak concentrations of this cluster are shown to be linearly correlated to the log of peak rainfall rates. <br><br> Parallel studies by Huffman et al. (2013) and Prenni et al. (2013) showed that the fluorescent particle concentrations correlated linearly with ice nuclei (IN) concentrations at this site during rain events. We discuss this result in conjunction with our cluster analysis to appraise the candidate IN.

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