Abstract
Abstract. 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) or UV-APS (ultraviolet aerodynamic particle sizer), for bioaerosol detection both outdoors and in the built environment. Significant work over several decades supported the development of the general technologies, but efforts to systematically characterize the operation of new commercial sensors have remained lacking. Specifically, 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, 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 the biological and non-biological particles directly using the five WIBS output parameters and by taking advantage of the particle classification analysis introduced by Perring et al. (2015). We highlight the importance that particle size plays on observed fluorescence properties and thus in the Perring-style particle classification. 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 significant impact on fluorescence fraction and particle type classification. We conclude that raising the fluorescence threshold from FT + 3σ to FT + 9σ does little to reduce the relative 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 carbon, diesel soot, and cotton fibers, and how these may impact WIBS analysis and data interpretation in various indoor and outdoor environments. The performance of the particle asymmetry factor (AF) reported by the instrument was assessed 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 includes size distributions broken down by fluorescent particle type for all 69 aerosol materials and comparing threshold strategies. Lastly, the study was 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 results.
Highlights
Biological material emitted into the atmosphere from biogenic sources on terrestrial and marine surfaces can play an important role in the health of many living systems and may influence diverse environmental processes (Cox and Wathes, 1995; Pöschl, 2005; Després et al, 2012; Fröhlich-Nowoisky et al, 2016)
We have aerosolized a representative list of pollen, fungal spores, and bacteria along with key aerosol types from the groups of fluorescing non-biological materials expected to be most problematic for ultraviolet laser/light-induced fluorescence (UV-LIF) instrumentation
The trend of particle fluorescence intensity and changing particle fluorescence type as a function of particle size was shown in detail
Summary
Biological material emitted into the atmosphere from biogenic sources on terrestrial and marine surfaces can play an important role in the health of many living systems and may influence diverse environmental processes (Cox and Wathes, 1995; Pöschl, 2005; Després et al, 2012; Fröhlich-Nowoisky et al, 2016). Bioaerosol exposure has been an increasingly important component of recent interest, motivated by studies linking airborne biological agents and adverse health effects in both indoor and occupational environments (Douwes et al, 2003). PBAP can include whole microorganisms, such as bacteria and viruses, reproductive entities (fungal spores and pollen), and small fragments of any larger biological material, such as leaves, vegetative detritus, fungal hyphae, or biopolymers, and can represent living, dead, dormant, pathogenic, allergenic, or biologically inert material (Després et al, 2012). PBAP often represent a large fraction of supermicron aerosol, for example up to 65 % by mass in pristine tropical forests, and may be present in high enough concentrations at submicron sizes to influence aerosol properties (Jaenicke, 2005; Penner, 1994; Pöschl et al, 2010)
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