Exploring the Relationship Between Filter Loading Effect and Aethalometer Multiple Scattering Enhancement Factor C in an Urban Background Site
ASTA GREGORIČ, Luca Ferrero, Matic Ivančič, Irena Ježek Brecelj, Bálint Alföldy, Martin Rigler, Aerosol d.o.o.
Abstract Number: 610
Working Group: Instrumentation and Methods
Abstract
An accurate determination of aerosol absorption coefficient (babs) is crucial for assessing the climate impact of light-absorbing aerosols. Filter photometers, commonly used for wide spectral range measurements (UV-IR) of babs, suffer from three key artifacts: a) multiple scattering effect due to enhanced optical path by filter fibers, b) backscattering of aerosol embedded in filter matrix, c) loading effect. While automatic loading effect compensation is integrated into Aethalometer software (using dual-spot method), the remaining two artefacts depend on filter material and aerosol optical properties and are compensated by the use of single parameter – multiple-scattering parameter C, which can be determined based on supplementary measurements of aerosol scattering coefficient [1] or by other reference measurements [2].
Recently, a novel method inferred C quantitatively based on intrinsic aerosol properties reflected in the loading compensation parameter [3]. Method provides MAAP complaint C characteristic for 660 nm.
Our study presents monthly resolved C values for a 3-year dataset, applied to calculate equivalent black carbon (eBC) and babs measured by Aethalometer AE33 (Aerosol Magee Scientific) at the urban background station in Ljubljana, Slovenia. Seasonal variations in C were observed, with lowest values (2.23) in winter and highest (3.6) in summer due to varying aerosol optical properties. The average C value (2.56 ± 0.39) closely aligns with Milan’s characteristics (2.51 ± 0.04) [3] and was found to be just slightly higher than 2.45 reported for the ACTRIS sites [4].
Monthly resolved determination of C value calculated from the loading effect compensation factors provides an efficient and reliable way to correct the eBC and babs results in near real time without the need for additional measurements.
[1] Yus-Díez, J. et al., AMT, 2021.
[2] Bernardoni, V. et al., AMT, 2021.
[3] Fererro, L. et. al. STOTEN, 2024
[4] Savadkoohi, M. et al., Env. Int., 2024.