Optimized instrument configurations for tandem particle mass analyzer and single particle-soot photometer experiments

Abstract

Tandem centrifugal particle mass analyzer (CPMA)-single-particle soot photometer (SP2) arrangements provide a measure of the non-refractory components of soot. In such a system, the CPMA is used to classify particles by mass-to-charge ratio (i.e., total particle mass mp), and the SP2 measures the mass of rBC (i.e., mrBC) within each particle. Data inversion can then be used to compute the two-dimensional total particle-non-refractory black carbon (rBC) (mp-mrBC) distribution, mapping out the distribution of non-refractory material on rBC particles. He present 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. Monte Carlo sampling is used to realize the sensitivity of reconstruction error to experimental inputs across a range of distribution widths. General recommendations for a typical aged atmospheric aerosol include: (i) large numbers of SP2 bins per decade (ns' = 64), (ii) a preference for higher SP2 sampling counts per CPMA setpoint (Ns > 104), (iii) a moderate number of CPMA setpoints per decade (nc’ = 3 to 8), (iv) CPMA resolution around 1.0, and (v) a high CPMA flow rate (1.5 L/min). These settings generally result in reconstruction accuracies below 3%. These recommendations vary based on the concentration of the aerosol, the time available for the measurement, and the width of the distribution. Optimized CPMA-SP2 settings are presented for example distributions as a function of aerosol concentration and desired measurement time.