Abstract View
Scattered Light Truncation Issues in the CAPS PM Single Scattering Albedo (CAPS PMssa) Monitor: Effects of Particle Size Distribution and Fefractive Index
FENGSHAN LIU, Joel Corbin, Prem Lobo, Gregory Smallwood, National Research Council Canada
Abstract Number: 546
Working Group: Instrumentation and Methods
Abstract
The cavity attenuated phase shift particulate matter single scattering albedo (CAPS PMssa) monitor has been increasingly used to measure aerosol absorption and single scattering albedo (SSA) based on the extinction-minus-scattering (EMS) principle for different applications. As with other nephelometers, CAPS PMssa also suffers from truncation issues in its scattering channel: part of the scattered light in the forward and backward directions cannot be detected. To achieve accurate measurements of both aerosol absorption and SSA, it is important to develop accurate truncation correction models to correct the measured aerosol scattering, especially for aerosols with a high SSA.
To date, limited numerical and experimental studies have been conducted to investigate the truncation issue of CAPS PMssa. To gain a more comprehensive and quantitative understanding of CAPS PMssa truncation, a numerical study was carried out to investigate the effects of aerosol particle size distribution and refractive index using our previously developed truncation model based on the radiative transfer equation (RTE). The aerosol particles considered in this study include both polydisperse non-absorbing and absorbing spherical polystyrene latex (PSL) particles and polydisperse absorbing fractal soot aggregates.
For aerosol measurements using CAPS PMssa, it is challenging to perform truncation correction to the measured scattering coefficient since the morphology, refractive index, or even the composition of aerosol particles are often unavailable. In most cases, only SSA and particle mobility or aerodynamic size distribution data are available. Our previous study showed that the truncation of CAPS PMssa correlates well with the asymmetry factor of the aerosol particle scattering phase function. To develop a practically usable truncation correction model, an attempt was made to estimate the range of asymmetry factor of aerosol particle scattering phase function based on SSA and particle mobility size distribution assuming PSL and soot particles represent two extreme types of aerosol particles in terms of morphology and refractive index.