Airborne observations of regional variation in fluorescent aerosol across the United States

Abstract

Airborne observations of fluorescent aerosol were made aboard an airship during CloudLab, a series of flights that took place in September and October of 2013 and covered a wideband of longitude across the continental U.S. between Florida and California and between 28 and 37 N latitudes. Sampling occurred from near the surface to 1000 m above the ground. A Wideband Integrated Bioaerosol Sensor (WIBS-4) measured average concentrations of supermicron fluorescent particles aloft (1 μm to 10 μm), revealing number concentrations ranging from 2.1 ± 0.8 to 8.7 ± 2.2 × 10 4 particles m À3 and representing up to 24% of total supermicron particle number. We observed distinct variations in size distributions and fluorescent characteristics in different regions, and attribute these to geographically diverse bioaerosol. Fluorescent aerosol detected in the east is largely consistent with mold spores observed in a laboratory setting, while a shift to larger sizes associated with different fluorescent patterns is observed in the west. Fluorescent bioaerosol loadings in the desert west were as high as those near the Gulf of Mexico, suggesting that bioaerosol is a substantial component of supermicron aerosol both in humid and arid environments. The observations are compared to model fungal and bacterial loading predictions, and good agreement in both particle size and concentrations is observed in the east. In the west, the model underestimated observed concentrations by a factor between 2 and 4 and the prescribed particle sizes are smaller than the observed fluorescent aerosol. A classification scheme for use with WIBS data is also presented.

Fluorescence calibration method for single-particle aerosol fluorescence instruments

“…We validated the procedure using a commercially available WIBS (model 4A), first described by Kaye et al (2005) and later in significant detail by Gabey et al (2010) and Perring et al (2015). We will briefly describe its operating principles and the instrument settings used in this study.…”

“…In general WIBS data analysis, FT data are used to determine a signal threshold for each channel above which a particle is considered fluorescent. In ambient measurements, where a majority of particles are non-fluorescent, the fluorescence threshold can be assessed without taking the instrument offline to run in FT mode, as there generally exists a dominant population of nonfluorescent particles that have a distribution of fluorescence magnitudes identical to the background data collected in FT mode (Perring et al, 2015). Here, sample particles were fluorescent by design and we use 2-5 min of FT mode data to determine fluorescence thresholds for each channel.…”

“…The use of these fluorescence magnitudes, however, varies widely in the published literature. Several recent studies have employed a binary yes-no classification of fluorescence above a threshold (e.g., Gabey et al, 2010;Perring et al, 2015), essentially ignoring the fluorescence magnitude beyond the threshold. Fluorescence magnitudes have been used as input variables in automated particle-clustering analyses (Robinson et al, 2013;Crawford et al, 2015) and to manually sort sampled particles into groupings (Wright et al, 2014).…”

Characterization of steady-state fluorescence properties of polystyrene latex spheres using off- and online spectroscopic methods

“…Many LIF instruments deployed for the rapid detection of bioaerosol particles have become commonly used within the bioaerosol community, and a growing number of instruments are commercially available (e.g., Huffman and Santarpia, 2017). The WIBS-4A, in particular, has been used for the purposes of both laboratory validations and longer-term ambient measurements (e.g., Healy et al, 2012;Hernandez et al, 2016;Huffman et al, 2013;O'Connor et al, 2013;Perring et al, 2015;Robinson et al, 2013;Savage et al, 2017;Toprak and Schnaiter, 2013). The WIBS-4A provides information about particle size, a light scattering asymmetry factor (AF, broadly related to particle shape), and fluorescence properties for individual particles in real time.…”

“…As a result, a number of real-time and commercial instruments including the Ultraviolet Aerodynamic Particle Sizer (UV-APS; TSI Inc., Shoreview, MN, USA) and the Waveband Integrated Bioaerosol Sensor (WIBS; Droplet Measurement Technologies, Longmont, CO, USA) are being commonly used in bioaerosol research communities (e.g., Agranovski et al, 2003;Bhangar et al, 2014;Brosseau et al, 2000;Foot et al, 2008;Huffman et al, 2010;Perring et al, 2015;Stanley et al, 2011;Toprak and Schnaiter, 2013). The main principle common to these techniques is the detection of intrinsic fluorescence from fluorophores such as amino acids, coenzymes, vitamins, and pigments that ubiquitously occur in aerosols of biological origin (e.g., Hill et al, 2009;Pan et al, 2010;Pöhlker et al, 2012Pöhlker et al, , 2013.…”