[A-AS11] Atmospheric Chemistry

[AAS11-27] Source-Specific Light Absorptivity of Organic Aerosols: Insights From a Year-long Offline Study in Hyytiälä, Finland

*Sun Qianzhe¹, Ruichen Zhou², Sho Ohata², Chiaki Shirota³, Tuukka Petäjä⁴, Lauri Ahonen⁴, Markku Kulmala⁴, Michihiro Mochida^1,2 (1.Graduate School of Environmental Studies, Nagoya University, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.Murata Keisokuki Service Co., Ltd., 4.Institute for Atmospheric and Earth System Research (INAR)/ Physics, University of Helsinki)

Keywords:aerosol , light absorption , source apportionment, boreal forest

Various and complex chemical compositions were exhibited by organic aerosols (OAs) from different emission sources, and their light-absorbing properties and the contributions from different light-absorbing components remain inadequately characterized. In this study, the sources of OAs and their light absorption characteristics in Hyytiälä Forest Station were investigated for submicrometer particles collected on filters in the period from July 2021 to June 2022. OA extract solutions were prepared according to their solubility and polarity as high-polarity fraction (HP-WSOM), humic-like substances (HULIS), and water-insoluble organic matter (WISOM). The fractions were analyzed by the offline use of a high-resolution aerosol mass spectrometer (AMS), and a UV–visible spectrophotometer. Among the fractions, HP-WSOM on average had the highest O/C ratio (0.93±0.23), followed by HULIS (0.60±0.06), and WISOM (0.28±0.05). Two distinct source apportionment solutions were obtained from positive matrix factorization for the OA fractions. Both solutions resolved three common sources: fossil fuel OA, biogenic secondary OA (BSOA), and more-oxidized oxygenated OA (MO-OOA). The 4-factor solution further differentiated biomass burning OA (BBOA) into two subtypes: BBOA1 (characterized by CHN-family ions, indicative of fresh biomass combustion) and BBOA2 (marked by aromatic compounds, associated with aged biomass material/fossil fuel burning). Notably, mass absorption efficiency (MAE) for HP-WSOM, HULIS, and WISOM showed strong positive correlations (R= 0.64 – 0.73) with CHN-family, which were characteristic ions of BBOA-1. Multilinear regression analysis with non-negative constraints revealed distinct MAE values for different factors: BBOA1 demonstrated significantly higher light-absorbing capacity (MAE= 0.98 m²/g) compared to BBOA2 (MAE= 0.34 m²/g), and contributed 72.5% of total OA light absorption. This study suggested the applicability of AMS-derived CHN-family ions as a tracer for BBOA, and would provide the first field evidence for differentiating the contributions of fresh and aged biomass material burning aerosols to light absorption.