Cluster analysis of WIBS single-particle bioaerosol data

Abstract

?? Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 LicenseHierarchical agglomerative cluster analysis was performed on single-particle multi-spatial data sets comprising optical diameter, asymmetry and three different ???uorescence measurements, gathered using two dual Wideband Integrated Bioaerosol Sensors (WIBSs). The technique is demonstrated on measurements of various ???uorescent and non-???uorescent polystyrene latex spheres (PSL) before being applied to two separate contemporaneous ambient WIBSdata sets recorded in a forest site in Colorado, USA, as part of the BEACHON-RoMBAS project. Cluster analysis results between both data sets are consistent. Clusters are tentatively interpreted by comparison of concentration time series and cluster average measurement values to the published literature (of which there is a paucity) to represent the following: non-???uorescent accumulation mode aerosol; bacterial agglomerates; and fungal spores. To our knowledge, this is the ???rst time cluster analysis has been applied to long-term online primary biological aerosol particle (PBAP) measurements. The novel application of this clustering technique provides a means for routinely reducing WIBS data to discrete concentration time series which are more easily interpretable, without the need for any a priori assumptions concerning the expected aerosol types. It can reduce the level of subjectivity compared to the more standard analysis approaches, which are typically performed by simple inspection of various ensemble data products. It also has the advantage of potentially resolving less populous or subtly different particle types. This technique is likely to become more robust in the future as ???uorescence-based aerosol instrumentation measurement precision, dynamic range and the number of available metrics are improved

Fluorescence calibration method for single-particle aerosol fluorescence instruments

“…Thus, the mass of tryptophan that saturates the FL1 detector at the high gain setting is ∼ 4 times lower than the low gain setting. As mentioned earlier, two WIBS clustering studies (Robinson et al, 2013;Crawford et al, 2015) excluded saturating particles from their analysis, and so understanding the range of measurable fluorophore mass is potentially important.…”

“…Perhaps loss of information may not matter to the user if they are employing a binary above-below threshold classification scheme, where the magnitudes of the fluorescence signals are not considered. On the other hand, as in the clustering study performed by Robinson et al (2013) in which saturating particles had to be excluded from analysis, a lower gain setting is likely optimal in most cases, as the dynamic range of measurable fluorophore mass is much larger. There may be considerable value in analyzing the fluorescence signal magnitudes in ambient data sets, and we recommend running instruments like the WIBS with gain settings that allow for the maximum range of mass determination.…”

“…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). Particles emitting so much fluorescence as to saturate detectors are sometimes excluded from analysis (e.g., Toprak and Schnaiter, 2013), and relatively weak fluorescence has been proposed as a possible discriminator of interfering nonbiological particles (Hill et al, 1999;Crawford et al, 2014Crawford et al, , 2016Yu et al, 2016).…”

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.…”

Photophoretic trapping-Raman spectroscopy for single pollens and fungal spores trapped in air

“…The technique was shown to be capable of differentiating pollens from various plant species [9,10]. Fluorescence clustering analysis, especially when it is combined with the dualwavelength UV-LIF, appears promising for rapid airborne bioaerosol characterization [11,12]. When excited at a visible wavelength, e.g., 488 nm, 515 nm, 633 nm, or 780 nm, most pollens and fungal spores have one or several fluorescence humps in a wide spectral range, e.g., 500-800 nm.…”