Sources, concentrations, and seasonal variations of VOC and aerosol particles in downtown Munich in 2023/24

Abstract. Only little is known about molecular composition and sources of air pollution in Germanys third largest city, Munich. Therefore, we investigated sources, concentrations, and seasonal variations of volatile organic compounds (VOC), semi-volatile organic aerosol (SVOA), and organic aerosol (OA) in an urban street canyon in Munich utilizing online mass spectrometry and positive matrix factorization (PMF). Organic aerosol concentrations were higher in summer (4.3 ± 2.9 µg m^-3) than late winter (3.3 ± 1.7 µg m^-3) due to enhanced photochemical reactions, while nitrate exhibited the opposite trend with elevated concentrations in winter (4.5 ± 3.2 µg m^-3) compared to summer (0.3 ± 0.2 µg m^-3). During summer heat, photochemistry generates low-volatile oxygenated OA (33 ± 20 %), while aged biomass burning organic aerosol (BBOA) (25 ± 21 %) from barbecue activities and biogenic OA (22 ± 14 %) from nocturnal monoterpene chemistry further shape aerosol composition. The colder seasons are characterized by combustion-derived aerosols (Winter: fresh BBOA 13 ± 9 %, aged 36 ± 12 %; Spring: fresh 27 ± 17 %, aged 37 ± 19 %), whose dynamics are driven mainly by anthropogenic activity patterns. Traffic contributed at this urban kerbside surprisingly little to aerosol mass (5–9 %) but more to VOC (22–35 %). Our findings point to efficient ways to improve air quality e.g. by reducing monoterpene emissions by urban vegetation management as well as reducing biomass burning including barbecue emissions, a major source of aerosol particles and precursor gases of secondary organic aerosol throughout the seasons.