Mapping Out the Absorption of Soot as a Function of Particle Mass Using CERMS and Laser-Induced Incandescence
RYM MEHRI, Joel Corbin, Timothy Sipkens, Fengshan Liu, Mark Johnson, Gregory Smallwood,
National Research Council Canada Abstract Number: 517
Working Group: Carbonaceous Aerosol
AbstractSoot has significant implications for health and the environment. Accurate measurement of soot light absorption is necessary to further understand its environmental impact and improve characterization techniques. The optical properties of soot (absorption and scattering) are often used to determine mass concentrations.
The centrifugal particle mass analyzer-electrometer reference mass system (CERMS) can be used to determine the mass of particulate in an aerosol stream. CERMS is composed of 1) a unipolar diffusion aerosol charger (UDAC) that uses a corona discharge to charge the particles positively or negatively, 2) a centrifugal particle mass analyzer (CPMA) to classify the particles based on their mass/charge ratio and 3) an aerosol electrometer to measure the charge concentration. The particle mass concentration can be determined based on the number of charged particles that reach the electrometer and the mass to charge ratio. When used with different mass instruments, CERMS can be used as a calibration system or to measure mass absorption cross-section (MAC) or absorption function E(m) based on the average particle mass. Previous studies have shown size dependence of soot MACs. The soot E(m), which is proportional to the MAC, is the optical parameter used in laser-induced incandescence (LII) instrument. Large variability has been reported for E(m), including how it may change with soot maturity and wavelength. In this study, we obtained a range of E(m) for soot emitted from a helicopter gas turbine engine by coupling CERMS with an LII. Measurements are supplemented with a scanning mobility particle sizer (SMPS) to provide size distributions of the classified particles. Through the measured E(m) as a function of particle size, MAC can be calculated and compared to data provided in the literature. This will help in further understanding soot’s light absorption and provide insights on the LII response as a function of particle size.