Characterization of Aerosol Types Using a 2D Angstrom Exponent Approach Across Multiple Sites
ASTA GREGORIČ, Matic Ivančič, Irena Ježek Brecelj, Gašper Lavrič, Bálint Alföldy, Albert Presto, Amalia Muñoz, Mila Ródenas, Luca Ferrero, Luca D'Angelo, Martin Gysel, Benjamin Brem, Marco Pandolfi, Jordi Rovira, Nikolaos Mihalopoulos, Panagiotis Kalkavouras, Tuukka Petäjä, Lauri Ahonen, Tobias Hammer, Konstantina Vasilatou, Martin Rigler, Aerosol d.o.o.
Abstract Number: 353
Working Group: Source Apportionment
Abstract
Aethalometers (AE33, AE36, AE36s, Aerosol Magee Scientific) are widely used to measure equivalent Black Carbon (BC) concentrations and source apportionment (SA), based on the absorption Ångström exponent (AAE) typically calculated from two wavelengths (470–950 nm). This method distinguishes BC from solid (biomass burning) and liquid fuel (fossil fuel – traffic related) combustion and is a well established source apportionment method for urban aerosol. However, aerosol absorption spectra often show complex features, particularly in the UV-visible range, that deviate from a single power-law model. These features are influenced by organic chromophores like Brown Carbon (BrC), whose absorption varies widely with chemical composition, photochemical aging, and mixing state with BC. Mineral dust and interactions with Aethalometer filter material also affect AAE measurements.
To improve source discrimination, we conducted measurements across several urban and remote locations from 2023 to 2025 using a 9-wavelength AE36s Aethalometer (340–950 nm), complemented by laboratory experiments with controlled aerosol sources. The AAE was analyzed in two spectral bands: AAE590–950 and AAE400–590, enabling differentiation between distinct absorption signatures.
Results show that traffic-related BC exhibits low AAE in both ranges, with minor spectral deviations due to transparent coatings. An increase in AAE400–590 indicates rising BrC contributions, allowing distinction between urban aerosols and fresh biomass-burning plumes. Saharan dust events were clearly separated by high AAE400–590 and consistently low AAE590–950 values.
This 2D AAE approach refines source apportionment in urban settings, improves detection of special events like Saharan dust intrusions, and allows for case-specific absorption coefficient corrections for improved accuracy in atmospheric assessments.