Sources, concentrations, and seasonal variations of VOC and aerosol particles in downtown Munich in 2023/2024

Abstract

Little is known about molecular composition and sources of air pollution in Germany's 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), consistent with 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 is associated with the formation of low-volatile oxygenated OA (33±20 %), while aged biomass burning organic aerosol (BBOA) (25±21 %) associated with barbecue activities and biogenic OA (22±14 %) linked to 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 relatively little to aerosol mass (5 %-9 %) but more to VOC (22 %-35 %). Our findings point to potential strategies to improve air quality e.g. by reducing monoterpene emissions by urban vegetation management as well as reducing biomass burning including barbecue emissions, which are attributed to a substantial fraction of aerosol particles and precursor gases of secondary organic aerosol throughout the seasons.