Real-time, single-particle fluorescence instruments used to detectatmospheric bioaerosol particles are increasingly common, yet no standardfluorescence calibration method exists for this technique. This gap limitsthe utility of these instruments as quantitative tools and complicatescomparisons between different measurement campaigns. To address this need, wehave developed a method to produce size-selected particles with a known massof fluorophore, which we use to calibrate the fluorescence detection of aWideband Integrated Bioaerosol Sensor (WIBS-4A). We use mixedtryptophan–ammonium sulfate particles to calibrate one detector (FL1;excitation = 280 nm, emission = 310–400 nm) and pure quinineparticles to calibrate the other (FL2; excitation = 280 nm, emission = 420–650 nm). The relationship between fluorescence and mass for the mixedtryptophan–ammonium sulfate particles is linear, while that for the purequinine particles is nonlinear, likely indicating that not all of thequinine mass contributes to the observed fluorescence. Nonetheless, bothmaterials produce a repeatable response between observed fluorescence andparticle mass. This procedure allows users to set the detector gains toachieve a known absolute response, calculate the limits of detection for agiven instrument, improve the repeatability of the instrumental setup, andfacilitate intercomparisons between different instruments. We recommendcalibration of single-particle fluorescence instruments using these methods.
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