Oxygenated Organic Aerosols in Munich: Molecular Characterization, Seasonal Variability, and Influence of Biomass Burning

Despite significant progress in air quality regulations, Munich still struggles with secondary pollutants such as aerosol particles and ozone. As air quality improves, organic aerosols are increasingly dominating urban atmospheric aerosols. However, the composition and variability of oxygenated organic aerosols remain highly complex and not well understood.

In this study, we conducted real-time field measurements of oxygenated organic aerosols in Munich—Germany's third-largest city—during the summer of 2023 and the spring of 2024, using thermal desorption ammonium chemical ionization mass spectrometry (NH₄⁺ CIMS). Our findings highlight the versatility of ammonium ions as a reagent for detecting atmospheric oxygenated organic aerosols. Throughout the campaign, we identified nearly 1,800 oxygenated organic compounds containing between 1 and 14 oxygen atoms. We analyzed and compared their molecular compositions, concentrations, diurnal variations, and volatilities between summer and spring. We also examined the sources and precursors of these aerosols by integrating data from other instruments, including an aerosol mass spectrometer, proton-transfer-reaction mass spectrometry, fiber-laser-induced fluorescence for formaldehyde, and various trace gas monitors. Notably, we observed a significant impact of biomass burning emissions on the concentration and composition of oxygenated organic aerosols in both seasons. This study will discuss the influence of different biomass burning activities on the observed features and urban air quality.