Abstract View
Optimized Sampling Settings and Reconstructions for Tandem Particle Mass Analyzer and Single Particle-Soot Photometer Measurements
Arash Naseri, Timothy Sipkens, Steven Rogak, JASON S. OLFERT, University of Alberta
Abstract Number: 270
Working Group: Instrumentation and Methods
Abstract
Black carbon (BC) is one of the main contributors of the anthropogenic radiative forcing underlying climate change. The short life cycle of BC and its presence in compound forms (e.g., mixed with or coated by other volatile and organic materials) makes isolating BC contributions to climate change challenging. Resolving these uncertainties requires robust measurements of the distribution of refractory BC mass and non-refractory (e.g. organic) coatings of atmospheric particles. A tandem arrangement of a centrifugal particle mass analyzer (CPMA) and single-particle soot photometer (SP2) provides a measure of the non-refractory components of BC. Data inversion can then be employed to reconstruct the two-dimensional total particle-non-refractory black carbon (rBC) (mp-mrBC) distribution, mapping out the distribution of non-refractory material on rBC particles. In such a measurement, the CPMA is used to sort out particles by mass-to-charge ratio, while the SP2 measures the mass of rBC within each particle. This study derives the optimum sampling settings (i.e., the number of CPMA setpoints per decade, the number of SP2 bins per decade, CPMA resolution, and the number of SP2 counts per CPMA setpoint) to accurately reconstruct mp-mrBC distributions, taking into account limitations in measurement duration (e.g., due to an unsteady aerosol source or the cost associated with drawn-out campaigns). Simulated measurements are combined with Monte Carlo sampling of the experimental settings to understand how experimental inputs contribute to reconstruction error. Optimized CPMA-SP2 settings are then presented for a typical atmospheric aerosol as a function of aerosol concentration and desired measurement time. Optimal sampling settings vary based on the concentration of the aerosol, the time available for the measurement, and the width of the distribution. Generally, we recommend: (i) large numbers of SP2 bins per decade (~ 50 to 100); (ii) a preference for higher SP2 sampling counts per CPMA setpoint (104); (iii) a moderate number of CPMA setpoints per decade (3 to 8); (iv) CPMA resolution around 1, and (v) a high CPMA flow rate (1.5 L/min), can be made to conduct the measurement in about an hour and achieve reconstruction accuracies below 3%.