Date of Award
Chemistry and Biochemistry
John A. Huffman, Ph.D.
Bioaerosol, Characterization, Fluorescence Threshold, Fluorescent Particles, UV-LIF, WIBS
Atmospheric particles of biological origin, also referred to as bioaerosols or primary biological aerosol particles (PBAP), are important to various human health and environmental systems. There has been a recent steep increase in the frequency of published studies utilizing commercial instrumentation based on ultraviolet laser/light-induced fluorescence (UV-LIF), such as the WIBS (wideband integrated bioaerosol sensor), for bioaerosol detection both outdoors and in the built environment. Significant work over several decades supported the development of these technologies, but efforts to systematically characterize the operation of new commercial sensors has remained lacking. Specifically, there are gaps in the understanding of how different classes of biological and non-biological particles can influence the detection ability of LIF-instrumentation.
In Chapter 2 we present the most comprehensive laboratory study of UV-LIF instrumentation ever reported, using 69 types of aerosol materials, including a representative list of pollen, fungal spores, and bacteria as well as the most important groups of non-biological materials reported to exhibit interfering fluorescent properties. Broad separation can be seen between biological and non-biological particles using the 5 data parameters delivered from the instrument. We highlight the importance that particle size plays on observed fluorescence properties and thus in the classification of particles. We also discuss several particle analysis strategies, including the use of different fluorescence thresholds. We conclude that raising the standard fluorescence baseline threshold can significantly reduce interference from mineral dust and other non-biological aerosols while contributing little to the reduction in signal from biological particles.
Preliminary work on a follow-up study (Chapter 3) utilized clustering techniques available in standard analysis software to investigate a method for improved discrimination between particle materials. This laboratory study focused on the separation of biological and interfering materials using an unsupervised method known as hierarchical agglomerative clustering (HAC). Previous studies have primarily focused on the separation (1) between standard particles types and (2) between particle types within ambient data sets. Little work has been done to understand the clustering process applied to controlled laboratory data or looking at the grouping efficiency of data preparation scenarios for biological and non-biological materials. Clustering results were optimized by inputting data in logarithmically-spaced bins and fluorescence intensity was not normalized to particle size, as had been done in previously published work. The clustering algorithm (Trial 1) successfully separated particles of Aspergillus niger (fungal spores) and diesel soot, which is a known interfering material due to its similar fluorescence characteristics as biological particles. Aspergillus niger and California sand, which was used as a surrogate for commonly observed, weakly fluorescent soil dust, showed relatively poor separation, which may have occurred as a result of the significant number of nonfluorescent particles involved in the analysis. The information gained from this study can help train data sets for supervised clustering methods with the hopes of better discrimination between particle materials.
Both studies were designed to propose analysis strategies that may be useful to the broader community of UV-LIF instrumentation users in order to promote deeper discussions about how best to continue improving UV-LIF instrumentation and analysis strategies.
Savage, Nicole Justine, "Improved Characterization and Analysis Strategies for UV-LIF Bioaerosol Instrumentation: Lab and Field Application" (2017). Electronic Theses and Dissertations. 1346.
Received from ProQuest
Nicole Justine Savage
Chemistry, Environmental science, Atmospheric sciences