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The Filter Inlet for Gases and AEROsols (FIGAERO) coupled with a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) enables online
measurements of both gas-phase and particle-phase chemical constituents of ambient aerosols. When properly calibrated, the incorporated particle
filter collection and subsequent thermal desorption enable the direct measurement of volatility of said constituents. Previously published
volatility calibration results however differ from each other significantly. In this study we investigate the reason for this discrepancy. We found
a major source of error in the widely used syringe deposition calibration method that can lead to an overestimation of saturation vapour pressures
by several orders of magnitude. We propose a new method for volatility calibration by using atomized calibration compounds that more accurately
captures the evaporation of chemical constituents from ambient aerosol particles. For example, we found a difference of ∼ 15 ∘C
in observed Tmax values between the atomizer method and syringe method using the lowest solution concentration (0.003 g L−1). This
difference translates into a difference of up to 3 orders of magnitude in saturation concentration C∗ space. We justify our claim with evaporation
modelling and direct scanning electron microscopy imaging, while also presenting possible error sources of the atomizer method. We finally present
how typical calibration parameters derived with both methods impact the volatility basis set (VBS) derived from measurements of secondary organic
aerosols (SOAs).