Characterization of water-soluble organic carbon absorption at an urban background site in the south-eastern Iberian Peninsula

Abstract

Measurements of absorption coefficients (σap,λ) and carbonaceous components (OC, EC, WSOC and levoglucosan) in PM1 were conducted at an urban background site in southeastern Spain throughout 2021. The main goal of this research was to determine the contribution from different sources to WSOC light absorption (σWSOC). For this, σBrC,λ values were previously obtained. The mean contribution of BrC to total aerosol absorption was ∼29% at 370 nm, revealing a significant influence of BrC to light absorption in the study area. Assuming that BrC light absorption was from WSOC and WIOC, a multilinear regression (MLR) model was used to estimate σWSOC and σWIOC. Average values (mean ± SD) were very similar for both components: σWSOC,370 = 1.6 (±0.7) Mm−1 and σWIOC,370 = 1.9 (±0.7) Mm−1. Finally, the PMF technique coupled with MLR analysis was used to identify the sources of WSOC light absorption and estimate their contribution. Our findings point to biomass burning as the dominant source of σWSOC during the cold season, with a contribution of ∼37%. The Mineral Dust and Secondary Nitrate sources, that were not included in the model due to their low contribution to WSOC mass concentrations, accounted for a significant percentage of σWSOC during this period. Secondary organic aerosol was the major source during the warm season (∼56%), followed by traffic emissions (∼30%).