Evaluation of mass measurement techniques for soot with different size distributions and OC ∕ TC contents

Abstract. This study focuses on measuring the mass concentration of soot aggregates generated with a Mini-CAST burner. The experiments were performed in a test bench able to generate soot particles with different size distributions and different organic to total carbon (OC/TC) ratios. With this soot production, we assessed the mass concentration measurements obtained with four online instruments, based on different methods: oscillating microbalance, aerosol electrical charging, filter photometry, and aerosol mobility, as well as an offline gravimetric measurement. The OC/TC ratio was determined by the thermal–optical method. The findings demonstrate that the oscillating microbalance measurements were performed within acceptable limits of 10 % in comparison to the gravimetric measurements, over a wide range of OC/TC ratio, mass concentration, and size distribution. The oscillating microbalance measurements were therefore considered to be the reference. The mass concentration measurement based on the aerosol electrical charging is calibrated for a reference size distribution, and we suggested a correction of the mass concentration measurement based on the aerosol Fuchs active surface, which proved to be efficient within the limits of this study. Finally, we confirmed that the mass concentration measurements obtained with the filter photometry method are OC/TC ratio and wavelength dependent, and we were able to establish OC/TC limits for the overall mass concentration evaluation with the infrared and ultraviolet wavelengths.