Abstract
Abstract. Real-time, single-particle fluorescence instruments used to detect atmospheric bioaerosol particles are increasingly common, yet no standard fluorescence calibration method exists for this technique. This gap limits the utility of these instruments as quantitative tools and complicates comparisons between different measurement campaigns. To address this need, we have developed a method to produce size-selected particles with a known mass of fluorophore, which we use to calibrate the fluorescence detection of a Wideband Integrated Bioaerosol Sensor (WIBS-4A). We use mixed tryptophan–ammonium sulfate particles to calibrate one detector (FL1; excitation = 280 nm, emission = 310–400 nm) and pure quinine particles to calibrate the other (FL2; excitation = 280 nm, emission = 420–650 nm). The relationship between fluorescence and mass for the mixed tryptophan–ammonium sulfate particles is linear, while that for the pure quinine particles is nonlinear, likely indicating that not all of the quinine mass contributes to the observed fluorescence. Nonetheless, both materials produce a repeatable response between observed fluorescence and particle mass. This procedure allows users to set the detector gains to achieve a known absolute response, calculate the limits of detection for a given instrument, improve the repeatability of the instrumental setup, and facilitate intercomparisons between different instruments. We recommend calibration of single-particle fluorescence instruments using these methods.
Highlights
Primary biological aerosol particles (PBAP) are of wide interest due to their potential impacts on air quality (e.g., Prussin II et al, 2015), ecology (e.g., Morris et al, 2013), and Earth’s climate (e.g., Creamean et al, 2013)
Compiled results from the tryptophan and quinine calibrations are shown in Fig. 4a and b, respectively, constructed as described above from single-particle fluorescence intensities measured for various fluorophore masses
We collected forced trigger (FT) mode data prior to each experiment, which is shown on these graphs
Summary
Primary biological aerosol particles (PBAP) are of wide interest due to their potential impacts on air quality (e.g., Prussin II et al, 2015), ecology (e.g., Morris et al, 2013), and Earth’s climate (e.g., Creamean et al, 2013). The measurement of atmospheric PBAP has historically involved offline techniques, such as culture-based methods and manual cell counting by optical fluorescence microscopy. These methods require long air sampling periods and significant post-collection labor, and they provide poor temporal resolution. In response to these shortcomings, a new generation of online, automated instruments for the measurement of PBAP, such as aerosol mass spectrometers (Tobias et al, 2005) and fluorescent particle spectrometers (Pan et al, 2003; Kaye et al, 2005), have recently been developed
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