Size-resolved elemental composition and arsenic speciation in urban aerosols from Oslo and Budapest

This study provides a detailed size-resolved analysis of atmospheric particulate matter (PM) collected in two contrasting European capitals, Oslo and Budapest, during summer and winter campaigns. Using 13-stage cascade impactors, we assessed the mass size distributions of over 30 elements and analyzed arsenic (As) compounds to identify their sources and potential health risks. Advanced data analyses, including Kaplan-Meier estimation for censored data, Atmospheric Particle Size Distribution (APSD) analysis, and Enrichment Factor (EF) calculations, revealed distinct behaviors among the elements. We observed a clear separation of sources based on particle size. Crustal elements such as aluminum (Al), iron (Fe), and calcium (Ca) were primarily found in the coarse mode (greater than 2.5 µm), originating from natural soil and resuspended road dust. In contrast, anthropogenic tracers like sulfur (S), As, cadmium (Cd), and lead (Pb) were concentrated in the accumulation mode (approximately 0.1-1.0 µm), which is characteristic of high-temperature combustion and secondary aerosol formation. A significant finding of our study was the predominance of inorganic arsenic (As_inorg) over organic species [dimethylarsinic acid (DMA) and trimethylarsine oxide (TMAO)] across all campaigns. As_inorg consistently peaked in the fine fraction and closely tracked the distribution of total As, indicating a substantial potential for deep respiratory deposition. Source apportionment analysis revealed notable seasonal and geographical differences. In Oslo, there was an accumulation-mode enrichment of vanadium (V) and nickel (Ni), indicating that shipping emissions were a major source of pollution. In Budapest, winter pollution was influenced by distinct local factors: potassium (K) shifted to the accumulation mode, pointing to biomass burning, while Pb exhibited a significant increase in the coarse mode, suggesting the resuspension of legacy soil contamination. These findings highlight the importance of size-resolved speciation for accurate source identification and health risk assessment in urban environments.