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Systematic characterization and fluorescence threshold strategies for the wideband integrated bioaerosol sensor (WIBS) using size-resolved biological and interfering particles

MPG-Autoren
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Könemann,  Tobias
Multiphase Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Pöhlker,  Christopher
Multiphase Chemistry, Max Planck Institute for Chemistry, Max Planck Society;

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Zitation

Savage, N. J., Krentz, C. E., Könemann, T., Han, T. T., Mainelis, G., Pöhlker, C., et al. (2017). Systematic characterization and fluorescence threshold strategies for the wideband integrated bioaerosol sensor (WIBS) using size-resolved biological and interfering particles. Atmospheric Measurement Techniques, 10(11), 4279-4302. doi:10.5194/amt-10-4279-2017.


Zitierlink: http://hdl.handle.net/11858/00-001M-0000-002E-8A54-1
Zusammenfassung
Atmospheric particles of biological origin, also re- ferred to as bioaerosols or primary biological aerosol parti- cles (PBAP), are important to various human health and en- vironmental systems. There has been a recent steep increase in the frequency of published studies utilizing commercial instrumentation based on ultraviolet laser/light-induced flu- orescence (UV-LIF), such as the WIBS (wideband inte- grated bioaerosol sensor) or UV-APS (ultraviolet aerody- namic particle sizer), for bioaerosol detection both outdoors and in the built environment. Significant work over several decades supported the development of the general technolo- gies, but efforts to systematically characterize the operation of new commercial sensors have remained lacking. Specif- ically, there have been gaps in the understanding of how different classes of biological and non-biological particles can influence the detection ability of LIF instrumentation. Here we present a systematic characterization of the WIBS- 4A instrument using 69 types of aerosol materials, includ- ing a representative list of pollen, fungal spores, and bacte- ria as well as the most important groups of non-biological materials reported to exhibit interfering fluorescent proper- ties. Broad separation can be seen between the biological and non-biological particles directly using the five WIBS output parameters and by taking advantage of the particle classifi- cation analysis introduced by Perring et al. (2015). We high- light the importance that particle size plays on observed fluo- rescence properties and thus in the Perring-style particle clas- sification. We also discuss several particle analysis strategies, including the commonly used fluorescence threshold defined as the mean instrument background (forced trigger; FT) plus 3 standard deviations ( σ) of the measurement. Changing the particle fluorescence threshold was shown to have a signifi- cant impact on fluorescence fraction and particle type classi- fication. We conclude that raising the fluorescence threshold from FT + 3 σ to FT + 9 σ does little to reduce the rela- tive fraction of biological material considered fluorescent but can significantly reduce the interference from mineral dust and other non-biological aerosols. We discuss examples of highly fluorescent interfering particles, such as brown car- bon, diesel soot, and cotton fibers, and how these may im- pact WIBS analysis and data interpretation in various indoor and outdoor environments. The performance of the particle asymmetry factor (AF) reported by the instrument was as- sessed across particle types as a function of particle size, and comments on the reliability of this parameter are given. A comprehensive online supplement is provided, which in- cludes size distributions broken down by fluorescent parti- cle type for all 69 aerosol materials and comparing threshold strategies. Lastly, the study was designed to propose analy- sis 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 results.