An inter-comparison of instruments measuring black carbon content of soot particles

Inter-comparison studies of well-characterized fractal Soot particles were conducted using the following four instruments: Aerosol Mass Spectrometer-Scanning Mobility Particle Sizer (AMS-SMPS), Single Particle Soot Photometer (SP2), Multi-Angle Absorption Photometer (MAAP), and Photoacoustic Spectrometer (PAS). These instruments provided measurements of the refractory mass (AMS-SMPS), incandescent mass (SP2) and optically absorbing mass (MAAP and PAS). The particles studied were in the mobility diameter range from 150 nm to 460 nm and were generated by controlled flames with fuel equivalence ratios ranging between 2.3 and 3.5. The effect of organic coatings (oleic acid and anthracene) on the instrument measurements was determined. For uncoated soot particles, the mass measurements by the AMS-SMPS, SP2, and PAS instruments were in agreement to within 15%, while the MAAP measurement of optically-absorbing mass was higher by similar to 50%. Thin organic coatings (similar to 10 nm) did not affect the instrument readings. A thicker (similar to 50 nm) oleic acid coating likewise did not affect the instrument readings. The thicker (similar to 60 nm) anthracene coating did not affect the readings provided by the AMS-SMPS or SP2 instruments but increased the reading of the MAAP instrument by similar to 20% and the reading of the PAS by similar to 65%. The response of each instrument to the different particle types is discussed in terms of particle morphology and coating material.