A Stable Water Dispersed Calibrant for Refractory Black Carbon (rBC) in the Soot Particle Aerosol Mass Spectrometer (SP-AMS)

ANITA AVERY, Edward Fortner, Leah Williams, Arthur J. Sedlacek, Shreya Joshi, Claudio Mazzoleni, Timothy Onasch, Aerodyne Research, Inc.

     Abstract Number: 424
     Working Group: Instrumentation and Methods

Abstract
The Aerodyne Soot-Particle Aerosol Mass Spectrometer (SP-AMS) utilizes a 1064 nm laser to vaporize refractory species before ionizing and detecting with a time-of-flight mass spectrometer. Quantifying the refractory black carbon (rBC) mass is performed via calibration with known quantities of regal black (RB, Regal 400, Cabot Corporation). Other calibrants can be used, including fullerene soot (for high Cx fragments), which is the standard calibrant for the Single Particle Soot Photometer (SP2, Droplet Measurement Technologies) and Cab-O-Jet (CJ, Cab-O-Jet 200 and 300, Cabot Corporation) which is used in black printing ink. Hydrophobic particles like RB are difficult to use in a standard, water-based atomizer and need to be continuously agitated to maintain a constant output, while CJ are stable in aqueous solution. Here we compare two types of CJ, with different surface functionality, with the standard SP-AMS calibrant, RB. We compare these for mass spectral similarities at C1-C5, particle beam width in the AMS, and relative ionization efficiency. CJ and RB exhibit nearly the same C1-C5 low carbon fragmentation pattern but show some differences in other spectral features related to the surface functional groups containing sulfur (CJ-200) or oxygen (CJ-300). Based on mass-mobility effective density measurements, the SP-AMS Cx sensitivity to CJ appears to be higher than to Regal Black. We explore this difference based on measured particle beam widths inside the SP-AMS and with scanning electron microscope (SEM) imaging. This work details the physical and mass spectral properties of RB and CJ and recommends a new calibration protocol based on CJ.