Observations of fluorescent and biological aerosol at a high-altitude site in central France

Abstract

Total bacteria, fungal spore and yeast counts were compared with ultraviolet-light-induced fluorescence (UV-LIF) measurements of ambient aerosol at the summit of the Puy de Dôme (PdD) mountain in central France (1465 m a.s.l), which represents a background elevated site. Bacteria, fungal spores and yeast were enumerated by epifluorescence microscopy (EFM) and found to number 2.2 to 23 L⁻¹ and 0.8 to 2 L⁻¹, respectively. Bacteria counts on two successive nights were an order of magnitude larger than in the intervening day. <br><br> A wide issue bioaerosol spectrometer, version 3 (WIBS-3) was used to perform UV-LIF measurements on ambient aerosol sized 0.8 to 20 μm. Mean total number concentration was 270 L⁻¹ (&sigma; = 66 L⁻¹), found predominantly in a size mode at 2 μm for most of the campaign. Total concentration (fluorescent + non-fluorescent aerosol) peaked at 500 L⁻¹ with a size mode at 1 μm because of a change in air mass origin lasting around 48 h. The WIBS-3 features two excitation and fluorescence detection wavelengths corresponding to different biological molecules, although non-biological interferents also contribute. The mean fluorescent particle concentration after short-wave (280 nm; associated with tryptophan) excitation was 12 L⁻¹ (&sigma; = 6 L⁻¹), and did not vary much throughout the campaign. In contrast, the mean concentration of particles fluorescent after long-wave (370 nm; associated with NADH) excitation was 95 L⁻¹ (&sigma; = 25 L⁻¹), and a nightly rise and subsequent fall of up to 100 L⁻¹ formed a strong diurnal cycle in the latter. The two fluorescent populations exhibited size modes at 3 μm and 2 to 3 μm, respectively. A hierarchical agglomerative cluster analysis algorithm was applied to the data and used to extract different particle factors. A cluster concentration time series representative of bacteria was identified. This was found to exhibit a diurnal cycle with a maximum peak appearing during the day. <br><br> Analysis of organic mass spectra recorded using an aerosol mass spectrometer (AMS; Aerodyne Inc.) suggests that aerosol reaching the site at night was more aged than that during the day, indicative of sampling the residual layer at night. Supplementary meteorological data and previous work also show that PdD lies in the residual layer/free troposphere at night, and this is thought to cause the observed diurnal cycles in organic-type and fluorescent aerosol particles. <br><br> Based on the observed disparity between bacteria and fluorescent particle concentrations, fluorescent non-PBA is likely to be important in the WIBS-3 data and the surprisingly high fluorescent concentration in the residual layer/free troposphere raises questions about a ubiquitous background in continental air during the summer

Measurements and modeling of surface–atmosphere exchange of microorganisms in Mediterranean grassland

“…A first attempt in this sense has been made in a pine forest by Crawford et al (2014). This method is very promising since it works independently from microbial culturability, even if research is still ongoing on discriminating between different PBA classes and between PBAs and nonbiological fluorescent compounds contaminating the signal (Gabey et al, 2013;Pöhlker et al, 2012;Toprak and Schnaiter, 2013). Single-particle mass spectrometry (SPMS) is also a technique that can be used to detect PBAs by relying on the spectroscopic detection of specific compounds that are assumed as a proxy of bioaerosols (Zawadowicz et al, 2017).…”

Regional-scale simulations of fungal spore aerosols using an emission parameterization adapted to local measurements of fluorescent biological aerosol particles

“…These non-biological process include particles from anthropogenic sources (e.g., polycyclic aromatic hydrocarbon particles from combustion and cigarette smoke), that are present most often in submicron aerosols , select oxidized organic aerosol particles (e.g., absorbing brown carbon particles) (Bones et al, 2010;Lee et al, 2013), and some humiclike substances (Gabey et al, 2013). For example, at the rural, elevated site of Puy de Dôme, France, WIBS-3 FBAP measurements were compared to results from fluorescence microscopy paired with staining of fungal spores and bacteria.…”

Chamber catalogues of optical and fluorescent signatures distinguish bioaerosol classes

“…When simultaneously reporting from multiple bandwidths, ultraviolet induced fluorescence (UV-LIF) has successfully detected airborne microbes in bench-scale chamber studies (Healy et al, 2012;Kaye et al, 2005;Toprak and Schnaiter, 2013) and been applied to support large-scale aerosol monitoring campaigns where fluorescent particle cohorts indicated significant bioaerosol contributions to airborne organic carbon pools (Gabey et al, 2010;Pöschl et al, 2010;Gabey et al, 2013;Perring et al, 2015).…”

“…While many PBAPs fluoresce, interpreting UV-LIF measurements for bioaerosol characterization presents significant interpretive challenges, some of which have been successfully addressed using cluster analyses (Pinnick et al, 2013;Gabey et al, 2013;Crawford et al, 2015;Pan et al, 2015). In addition to classic Bayesian clustering approaches, referential methods can also be applied to analyze fluorescence distributions with selected optical properties, which may in turn be leveraged for environmental comparison(s).…”