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Abstract

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.