AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
A Novel Inversion Method to Calculate the Mass Fraction of Coated Refractory Black Carbon Using a Centrifugal Particle Mass Analyzer and Single Particle Soot Photometer
Kurtis Broda, JASON S. OLFERT, Martin Irwin, Gregory Schill, Gavin McMeeking, Elijah G. Schnitzler, Wolfgang Jager, University of Alberta
Abstract Number: 148 Working Group: Instrumentation and Methods
Abstract Refractory black carbon (rBC) has important atmospheric impacts due to its ability to absorb light, and its interactions with light are partly governed by acquisition of coatings or other mixing processes. Here, a novel inversion method is presented that derives the mass fraction of coated rBC using a coupled centrifugal particle mass analyzer (CPMA) and single particle soot photometer (SP2). The CPMA classifies all particles by their mass-to-charge ratio, and the SP2 detects the mass of rBC in each individual particle. The inversion outputs the simultaneous number distribution of both rBC mass and total particle mass. The distribution can be integrated to find properties of the total aerosol population including the mass fraction of coating and the mass of coating on a particle of known total mass. These capabilities were demonstrated via smog chamber experiments, initially, particles in the chamber were pure rBC. An organic (non-rBC) coating was grown onto the aerosol over several hours via photooxidation of p-xylene. As the coating grew, the CPMA-SP2 system sampled the aerosol. The CPMA was sequentially stepped over a mass range from 0.3 to 28 fg and the SP2 measured the mass of rBC in each individual CPMA-classified particle. Number and mass distributions were constructed using the inversion. As expected, the mass and number distributions of rBC and total mass were equivalent for uncoated particles. As the non-rBC coating thickness increased over time, the number distribution shifted towards a higher total mass. After several hours of sampling, fresh uncoated rBC particles were injected into the chamber creating an external mixture of coated and uncoated particles. This external mixture was clearly resolved in the number distribution of rBC and total particle mass. The CPMA-SP2 method offers several advantages over SP2 only methods namely, i) coating mass information can be obtained over a much wider range of particle mass (restricted in the SP2 by sensitivity to light scattered by rBC), ii) coating mass is measured directly (i.e., no assumptions for coating density or refractive index), and iii) does not make morphology assumptions (e.g. core-shell).