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Evaluation of a Hierarchical Agglomerative Clustering Method Applied to WIBS Laboratory Data for Improved Discrimination of Biological Particles by Comparing Data Preparation Techniques

Preprint published in 2018 by Nicole Savage, J. Alex Huffman
This paper is available in a repository.
This paper is available in a repository.

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Preprint: policy unknown
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Postprint: policy unknown
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Abstract

Hierarchical agglomerative clustering (HAC) analysis has been successfully applied to several sets of ambient data (e.g. Crawford et al., 2015; Robinson et al., 2013) and with respect to standardized particles in the laboratory environment (Ruske et al., 2017). Here we show for the first time a systematic application of HAC to a comprehensive set of laboratory data collected using the wideband integrated bioaerosol sensor (WIBS-4A) (Savage et al., 2017). The impact of particle ratio on HAC results was investigated, showing that clustering quality can vary dramatically as a function of ratio. Six strategies for particle pre-processing were also compared, concluding that using raw fluorescence intensity (without normalizing to particle size) and inputting all data in logarithmic bins consistently produced the highest quality results. A total of 23 one-on-one matchups of individual particles types were investigated. Results showed cluster misclassification of < 15 % for 12 of 17 analytical experiments using one biological and one non-biological particle type each. Inputting fluorescence data using a baseline +3σ threshold produced lower misclassification than when inputting either all particles (without fluorescence threshold) or a baseline +9σ threshold. Lastly, six synthetic mixtures of four to seven components were analyzed. These results show that a range of 12–24 % of fungal clusters were consistently misclassified by inclusion of a mixture of non-biological materials, whereas bacteria and diesel soot were each able to be separated with nearly 100 % efficiency. The study gives significant support to the application of clustering analysis to data from commercial UV-LIF instruments being commonly used for bioaerosol research across the globe and provides practical tools that will improve clustering results within scientific studies as a part of diverse research disciplines.

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