American Association for Aerosol Research - Abstract Submission

AAAR 39th Annual Conference
October 18 - October 22, 2021

Virtual Conference

Abstract View


Improvements to the Virkkula Filter Correction Algorithm for Measuring Carbonaceous Aerosol Optical Properties

THEO PAIK, Patrick Sheridan, Rajan K. Chakrabarty, Washington University in St. Louis

     Abstract Number: 445
     Working Group: Aerosol Standards

Abstract
Filter-based instruments, such as the particle soot absorption photometer (PSAP), are used to measure and constrain aerosol optical properties and related parameters at multiple sites worldwide. These filter-based optical measurements are subject to significant artifacts that depend on a given filter measurement system and aerosol optics. Resulting errors due to these artifacts could propagate into radiative transfer models that rely on filter-based optical data sets. Several correction algorithms have been proposed to align filter-based aerosol absorption data sets with standard reference particle-phase absorption measurements through process-based correction. Notably, Virkkula (2010) developed a simple correction scheme based on measurements of kerosene soot and “white” ammonium sulfate aerosol using a three-wavelength PSAP. Currently, the Virkkula correction algorithm is widely implemented for inferring particle-phase optical properties from filter-based measurements. It is, however, unclear how this algorithm performs for atmospherically relevant carbonaceous aerosol with spectrally-varying absorbing properties and single scattering albedo (SSA). Additionally, the applicability of this algorithm for newer filter-based optical instruments, such as the tricolor absorption photometer (TAP), has not been thoroughly evaluated. Here, we generated carbonaceous aerosol emissions with a wide range of spectrally-varying optical properties from laboratory biomass combustion. These aerosols were simultaneously sampled using a TAP, a tricolor PSAP, and integrated photoacoustic-nephelometer spectrometers at wavelengths comparable to the two filter-based photometers. First, we tested the validity of the original Virkkula’s correction scheme. Next, we provide improved correction factors for the Virkkula algorithm as a function of absorbing aerosol type and SSA that could be readily implemented for analyzing archived datasets and future measurements.

Reference:
A. Virkkula, Aerosol Sci. Technol. 44, 706 (2010).